Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

13 files changed, 3608 insertions, 0 deletions

diff --git a/build/unix/elfhack/Makefile.in b/build/unix/elfhack/Makefile.in
new file mode 100644
index 0000000000..620f17f3c4
--- /dev/null
+++ b/build/unix/elfhack/Makefile.in
@@ -0,0 +1,44 @@
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+include $(topsrcdir)/config/rules.mk
+
+ifdef COMPILE_ENVIRONMENT
+test-array$(DLL_SUFFIX) test-ctors$(DLL_SUFFIX): %$(DLL_SUFFIX): %.$(OBJ_SUFFIX) elfhack
+	$(MKSHLIB) $(LDFLAGS) $< -nostartfiles
+	@echo ===
+	@echo === If you get failures below, please file a bug describing the error
+	@echo === and your environment \(compiler and linker versions\), and
+	@echo === provide the pre-elfhacked library as an attachment.
+	@echo === Use --disable-elf-hack until this is fixed.
+	@echo ===
+	# Fail if the library doesn't have $(DT_TYPE) .dynamic info
+	$(READELF) -d $@ | grep '($(DT_TYPE))'
+	@rm -f $@.bak
+	$(CURDIR)/elfhack -b -f $@
+	# Fail if the backup file doesn't exist
+	[ -f '$@.bak' ]
+	# Fail if the new library doesn't contain less relocations
+	[ $$($(READELF) -r $@.bak | wc -l) -gt $$($(READELF) -r $@ | wc -l) ]
+
+test-array$(DLL_SUFFIX) test-ctors$(DLL_SUFFIX): DSO_SONAME=$@
+test-array$(DLL_SUFFIX): DT_TYPE=INIT_ARRAY
+test-ctors$(DLL_SUFFIX): DT_TYPE=INIT
+
+libs:: test-array$(DLL_SUFFIX) test-ctors$(DLL_SUFFIX)
+
+.PRECIOUS: test-array$(DLL_SUFFIX) test-ctors$(DLL_SUFFIX)
+
+ifndef CROSS_COMPILE
+dummy: dummy.$(OBJ_SUFFIX)
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+libs:: dummy
+	# Will either crash or return exit code 1 if elfhack is broken
+	LD_PRELOAD=$(CURDIR)/test-array$(DLL_SUFFIX) $(CURDIR)/dummy
+	LD_PRELOAD=$(CURDIR)/test-ctors$(DLL_SUFFIX) $(CURDIR)/dummy
+
+endif
+endif
diff --git a/build/unix/elfhack/README b/build/unix/elfhack/README
new file mode 100644
index 0000000000..8c68031e33
--- /dev/null
+++ b/build/unix/elfhack/README
@@ -0,0 +1,28 @@
+Elfhack is a program to optimize ELF binaries for size and cold startup
+speed.
+
+Presently, it is quite experimental, though it works well for the target
+it was created for: Firefox's libxul.so.
+
+Elfhack currently only does one thing: packing dynamic relocations ;
+which ends up being a quite complex task, that can be summarized this
+way:
+- Remove RELATIVE relocations from the .rel.dyn/.rela.dyn section.
+- Inject a small code able to apply relative relocations "by hand"
+  after the .rel.dyn/.rela.dyn section.
+- Inject a section containing relocative relocations in a different
+  and more packed format, after the small code.
+- Register the small code as DT_INIT function. Make the small code call
+  what was initially the DT_INIT function, if there was one.
+- Remove the hole between the new section containing relative
+  relocations and the following sections, adjusting offsets and base
+  addresses accordingly.
+- Adjust PT_LOAD entries to fit new offsets, and add an additional
+  PT_LOAD entry when that is necessary to handle the discrepancy between
+  offsets and base addresses, meaning the section offsets may yet again
+  need adjustments.
+- Adjust various DT_* dynamic tags to fit the new ELF layout.
+- Adjust section headers.
+- Adjust ELF headers.
+
+See http://glandium.org/blog/?p=1177#relocations for some figures.
diff --git a/build/unix/elfhack/dummy.c b/build/unix/elfhack/dummy.c
new file mode 100644
index 0000000000..2cde16102e
--- /dev/null
+++ b/build/unix/elfhack/dummy.c
@@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+extern __attribute__((visibility("default"), weak)) int print_status();
+
+int main() { return print_status(); }
diff --git a/build/unix/elfhack/elf.cpp b/build/unix/elfhack/elf.cpp
new file mode 100644
index 0000000000..8a759e8b09
--- /dev/null
+++ b/build/unix/elfhack/elf.cpp
@@ -0,0 +1,935 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#undef NDEBUG
+#include <cstring>
+#include <assert.h>
+#include "elfxx.h"
+
+template <class endian, typename R, typename T>
+void Elf_Ehdr_Traits::swap(T& t, R& r) {
+  memcpy(r.e_ident, t.e_ident, sizeof(r.e_ident));
+  r.e_type = endian::swap(t.e_type);
+  r.e_machine = endian::swap(t.e_machine);
+  r.e_version = endian::swap(t.e_version);
+  r.e_entry = endian::swap(t.e_entry);
+  r.e_phoff = endian::swap(t.e_phoff);
+  r.e_shoff = endian::swap(t.e_shoff);
+  r.e_flags = endian::swap(t.e_flags);
+  r.e_ehsize = endian::swap(t.e_ehsize);
+  r.e_phentsize = endian::swap(t.e_phentsize);
+  r.e_phnum = endian::swap(t.e_phnum);
+  r.e_shentsize = endian::swap(t.e_shentsize);
+  r.e_shnum = endian::swap(t.e_shnum);
+  r.e_shstrndx = endian::swap(t.e_shstrndx);
+}
+
+template <class endian, typename R, typename T>
+void Elf_Phdr_Traits::swap(T& t, R& r) {
+  r.p_type = endian::swap(t.p_type);
+  r.p_offset = endian::swap(t.p_offset);
+  r.p_vaddr = endian::swap(t.p_vaddr);
+  r.p_paddr = endian::swap(t.p_paddr);
+  r.p_filesz = endian::swap(t.p_filesz);
+  r.p_memsz = endian::swap(t.p_memsz);
+  r.p_flags = endian::swap(t.p_flags);
+  r.p_align = endian::swap(t.p_align);
+}
+
+template <class endian, typename R, typename T>
+void Elf_Shdr_Traits::swap(T& t, R& r) {
+  r.sh_name = endian::swap(t.sh_name);
+  r.sh_type = endian::swap(t.sh_type);
+  r.sh_flags = endian::swap(t.sh_flags);
+  r.sh_addr = endian::swap(t.sh_addr);
+  r.sh_offset = endian::swap(t.sh_offset);
+  r.sh_size = endian::swap(t.sh_size);
+  r.sh_link = endian::swap(t.sh_link);
+  r.sh_info = endian::swap(t.sh_info);
+  r.sh_addralign = endian::swap(t.sh_addralign);
+  r.sh_entsize = endian::swap(t.sh_entsize);
+}
+
+template <class endian, typename R, typename T>
+void Elf_Dyn_Traits::swap(T& t, R& r) {
+  r.d_tag = endian::swap(t.d_tag);
+  r.d_un.d_val = endian::swap(t.d_un.d_val);
+}
+
+template <class endian, typename R, typename T>
+void Elf_Sym_Traits::swap(T& t, R& r) {
+  r.st_name = endian::swap(t.st_name);
+  r.st_value = endian::swap(t.st_value);
+  r.st_size = endian::swap(t.st_size);
+  r.st_info = t.st_info;
+  r.st_other = t.st_other;
+  r.st_shndx = endian::swap(t.st_shndx);
+}
+
+template <class endian>
+struct _Rel_info {
+  static inline void swap(Elf32_Word& t, Elf32_Word& r) { r = endian::swap(t); }
+  static inline void swap(Elf64_Xword& t, Elf64_Xword& r) {
+    r = endian::swap(t);
+  }
+  static inline void swap(Elf64_Xword& t, Elf32_Word& r) {
+    r = endian::swap(ELF32_R_INFO(ELF64_R_SYM(t), ELF64_R_TYPE(t)));
+  }
+  static inline void swap(Elf32_Word& t, Elf64_Xword& r) {
+    r = endian::swap(ELF64_R_INFO(ELF32_R_SYM(t), ELF32_R_TYPE(t)));
+  }
+};
+
+template <class endian, typename R, typename T>
+void Elf_Rel_Traits::swap(T& t, R& r) {
+  r.r_offset = endian::swap(t.r_offset);
+  _Rel_info<endian>::swap(t.r_info, r.r_info);
+}
+
+template <class endian, typename R, typename T>
+void Elf_Rela_Traits::swap(T& t, R& r) {
+  r.r_offset = endian::swap(t.r_offset);
+  _Rel_info<endian>::swap(t.r_info, r.r_info);
+  r.r_addend = endian::swap(t.r_addend);
+}
+
+static const Elf64_Shdr null64_section = {0, SHT_NULL,  0, 0, 0,
+                                          0, SHN_UNDEF, 0, 0, 0};
+
+Elf_Shdr null_section(null64_section);
+
+Elf_Ehdr::Elf_Ehdr(std::ifstream& file, unsigned char ei_class,
+                   unsigned char ei_data)
+    : serializable<Elf_Ehdr_Traits>(file, ei_class, ei_data),
+      ElfSection(null_section, nullptr, nullptr) {
+  shdr.sh_size = Elf_Ehdr::size(ei_class);
+}
+
+Elf::Elf(std::ifstream& file) {
+  if (!file.is_open()) throw std::runtime_error("Error opening file");
+
+  file.exceptions(std::ifstream::eofbit | std::ifstream::failbit |
+                  std::ifstream::badbit);
+  // Read ELF magic number and identification information
+  unsigned char e_ident[EI_VERSION];
+  file.seekg(0);
+  file.read((char*)e_ident, sizeof(e_ident));
+  file.seekg(0);
+  ehdr = new Elf_Ehdr(file, e_ident[EI_CLASS], e_ident[EI_DATA]);
+
+  // ELFOSABI_LINUX is kept unsupported because I haven't looked whether
+  // STB_GNU_UNIQUE or STT_GNU_IFUNC would need special casing.
+  if ((ehdr->e_ident[EI_OSABI] != ELFOSABI_NONE) &&
+      (ehdr->e_ident[EI_ABIVERSION] != 0))
+    throw std::runtime_error("unsupported ELF ABI");
+
+  if (ehdr->e_version != 1) throw std::runtime_error("unsupported ELF version");
+
+  // Sanity checks
+  if (ehdr->e_shnum == 0)
+    throw std::runtime_error("sstripped ELF files aren't supported");
+
+  if (ehdr->e_ehsize != Elf_Ehdr::size(e_ident[EI_CLASS]))
+    throw std::runtime_error(
+        "unsupported ELF inconsistency: ehdr.e_ehsize != sizeof(ehdr)");
+
+  if (ehdr->e_shentsize != Elf_Shdr::size(e_ident[EI_CLASS]))
+    throw std::runtime_error(
+        "unsupported ELF inconsistency: ehdr.e_shentsize != sizeof(shdr)");
+
+  if (ehdr->e_phnum == 0) {
+    if (ehdr->e_phoff != 0)
+      throw std::runtime_error(
+          "unsupported ELF inconsistency: e_phnum == 0 && e_phoff != 0");
+    if (ehdr->e_phentsize != 0)
+      throw std::runtime_error(
+          "unsupported ELF inconsistency: e_phnum == 0 && e_phentsize != 0");
+  } else if (ehdr->e_phoff != ehdr->e_ehsize)
+    throw std::runtime_error(
+        "unsupported ELF inconsistency: ehdr->e_phoff != ehdr->e_ehsize");
+  else if (ehdr->e_phentsize != Elf_Phdr::size(e_ident[EI_CLASS]))
+    throw std::runtime_error(
+        "unsupported ELF inconsistency: ehdr->e_phentsize != sizeof(phdr)");
+
+  // Read section headers
+  Elf_Shdr** shdr = new Elf_Shdr*[ehdr->e_shnum];
+  file.seekg(ehdr->e_shoff);
+  for (int i = 0; i < ehdr->e_shnum; i++)
+    shdr[i] = new Elf_Shdr(file, e_ident[EI_CLASS], e_ident[EI_DATA]);
+
+  // Sanity check in section header for index 0
+  if ((shdr[0]->sh_name != 0) || (shdr[0]->sh_type != SHT_NULL) ||
+      (shdr[0]->sh_flags != 0) || (shdr[0]->sh_addr != 0) ||
+      (shdr[0]->sh_offset != 0) || (shdr[0]->sh_size != 0) ||
+      (shdr[0]->sh_link != SHN_UNDEF) || (shdr[0]->sh_info != 0) ||
+      (shdr[0]->sh_addralign != 0) || (shdr[0]->sh_entsize != 0))
+    throw std::runtime_error(
+        "Section header for index 0 contains unsupported values");
+
+  if ((shdr[ehdr->e_shstrndx]->sh_link != 0) ||
+      (shdr[ehdr->e_shstrndx]->sh_info != 0))
+    throw std::runtime_error(
+        "unsupported ELF content: string table with sh_link != 0 || sh_info != "
+        "0");
+
+  // Store these temporarily
+  tmp_shdr = shdr;
+  tmp_file = &file;
+
+  // Fill sections list
+  sections = new ElfSection*[ehdr->e_shnum];
+  for (int i = 0; i < ehdr->e_shnum; i++) sections[i] = nullptr;
+  for (int i = 1; i < ehdr->e_shnum; i++) {
+    // The .dynamic section is going to have references to other sections,
+    // so it's better to start with that one and recursively initialize those
+    // other sections first, to avoid possible infinite recursion (bug 1606739).
+    if (tmp_shdr[i]->sh_type == SHT_DYNAMIC) {
+      getSection(i);
+    }
+  }
+  for (int i = 1; i < ehdr->e_shnum; i++) {
+    if (sections[i] != nullptr) continue;
+    getSection(i);
+  }
+  Elf_Shdr s;
+  s.sh_name = 0;
+  s.sh_type = SHT_NULL;
+  s.sh_flags = 0;
+  s.sh_addr = 0;
+  s.sh_offset = ehdr->e_shoff;
+  s.sh_entsize = Elf_Shdr::size(e_ident[EI_CLASS]);
+  s.sh_size = s.sh_entsize * ehdr->e_shnum;
+  s.sh_link = 0;
+  s.sh_info = 0;
+  s.sh_addralign = (e_ident[EI_CLASS] == ELFCLASS32) ? 4 : 8;
+  shdr_section = new ElfSection(s, nullptr, nullptr);
+
+  // Fake section for program headers
+  s.sh_offset = ehdr->e_phoff;
+  s.sh_addr = ehdr->e_phoff;
+  s.sh_entsize = Elf_Phdr::size(e_ident[EI_CLASS]);
+  s.sh_size = s.sh_entsize * ehdr->e_phnum;
+  phdr_section = new ElfSection(s, nullptr, nullptr);
+
+  phdr_section->insertAfter(ehdr, false);
+
+  sections[1]->insertAfter(phdr_section, false);
+  for (int i = 2; i < ehdr->e_shnum; i++) {
+    // TODO: this should be done in a better way
+    if ((shdr_section->getPrevious() == nullptr) &&
+        (shdr[i]->sh_offset > ehdr->e_shoff)) {
+      shdr_section->insertAfter(sections[i - 1], false);
+      sections[i]->insertAfter(shdr_section, false);
+    } else
+      sections[i]->insertAfter(sections[i - 1], false);
+  }
+  if (shdr_section->getPrevious() == nullptr)
+    shdr_section->insertAfter(sections[ehdr->e_shnum - 1], false);
+
+  tmp_file = nullptr;
+  tmp_shdr = nullptr;
+  for (int i = 0; i < ehdr->e_shnum; i++) delete shdr[i];
+  delete[] shdr;
+
+  eh_shstrndx = (ElfStrtab_Section*)sections[ehdr->e_shstrndx];
+
+  // Skip reading program headers if there aren't any
+  if (ehdr->e_phnum == 0) return;
+
+  bool adjusted_phdr_section = false;
+  // Read program headers
+  file.seekg(ehdr->e_phoff);
+  for (int i = 0; i < ehdr->e_phnum; i++) {
+    Elf_Phdr phdr(file, e_ident[EI_CLASS], e_ident[EI_DATA]);
+    if (phdr.p_type == PT_LOAD) {
+      // Default alignment for PT_LOAD on x86-64 prevents elfhack from
+      // doing anything useful. However, the system doesn't actually
+      // require such a big alignment, so in order for elfhack to work
+      // efficiently, reduce alignment when it's originally the default
+      // one.
+      if ((ehdr->e_machine == EM_X86_64) && (phdr.p_align == 0x200000))
+        phdr.p_align = 0x1000;
+    }
+    ElfSegment* segment = new ElfSegment(&phdr);
+    // Some segments aren't entirely filled (if at all) by sections
+    // For those, we use fake sections
+    if ((phdr.p_type == PT_LOAD) && (phdr.p_offset == 0)) {
+      // Use a fake section for ehdr and phdr
+      ehdr->getShdr().sh_addr = phdr.p_vaddr;
+      if (!adjusted_phdr_section) {
+        phdr_section->getShdr().sh_addr += phdr.p_vaddr;
+        adjusted_phdr_section = true;
+      }
+      segment->addSection(ehdr);
+      segment->addSection(phdr_section);
+    }
+    if (phdr.p_type == PT_PHDR) {
+      if (!adjusted_phdr_section) {
+        phdr_section->getShdr().sh_addr = phdr.p_vaddr;
+        adjusted_phdr_section = true;
+      }
+      segment->addSection(phdr_section);
+    }
+    for (int j = 1; j < ehdr->e_shnum; j++)
+      if (phdr.contains(sections[j])) segment->addSection(sections[j]);
+    // Make sure that our view of segments corresponds to the original
+    // ELF file.
+    // GNU gold likes to start some segments before the first section
+    // they contain. https://sourceware.org/bugzilla/show_bug.cgi?id=19392
+    unsigned int gold_adjustment = segment->getAddr() - phdr.p_vaddr;
+    assert(segment->getFileSize() == phdr.p_filesz - gold_adjustment);
+    // gold makes TLS segments end on an aligned virtual address, even
+    // when the underlying section ends before that, while bfd ld
+    // doesn't. It's fine if we don't keep that alignment.
+    unsigned int memsize = segment->getMemSize();
+    if (phdr.p_type == PT_TLS && memsize != phdr.p_memsz) {
+      unsigned int align = segment->getAlign();
+      memsize = (memsize + align - 1) & ~(align - 1);
+    }
+    assert(memsize == phdr.p_memsz - gold_adjustment);
+    segments.push_back(segment);
+  }
+
+  new (&eh_entry) ElfLocation(ehdr->e_entry, this);
+}
+
+Elf::~Elf() {
+  for (std::vector<ElfSegment*>::iterator seg = segments.begin();
+       seg != segments.end(); seg++)
+    delete *seg;
+  delete[] sections;
+  ElfSection* section = ehdr;
+  while (section != nullptr) {
+    ElfSection* next = section->getNext();
+    delete section;
+    section = next;
+  }
+}
+
+// TODO: This shouldn't fail after inserting sections
+ElfSection* Elf::getSection(int index) {
+  if ((index < -1) || (index >= ehdr->e_shnum))
+    throw std::runtime_error("Section index out of bounds");
+  if (index == -1)
+    index = ehdr->e_shstrndx;  // TODO: should be fixed to use the actual
+                               // current number
+  // Special case: the section at index 0 is void
+  if (index == 0) return nullptr;
+  // Infinite recursion guard
+  if (sections[index] == (ElfSection*)this) return nullptr;
+  if (sections[index] == nullptr) {
+    sections[index] = (ElfSection*)this;
+    switch (tmp_shdr[index]->sh_type) {
+      case SHT_DYNAMIC:
+        sections[index] =
+            new ElfDynamic_Section(*tmp_shdr[index], tmp_file, this);
+        break;
+      case SHT_REL:
+        sections[index] =
+            new ElfRel_Section<Elf_Rel>(*tmp_shdr[index], tmp_file, this);
+        break;
+      case SHT_RELA:
+        sections[index] =
+            new ElfRel_Section<Elf_Rela>(*tmp_shdr[index], tmp_file, this);
+        break;
+      case SHT_DYNSYM:
+      case SHT_SYMTAB:
+        sections[index] =
+            new ElfSymtab_Section(*tmp_shdr[index], tmp_file, this);
+        break;
+      case SHT_STRTAB:
+        sections[index] =
+            new ElfStrtab_Section(*tmp_shdr[index], tmp_file, this);
+        break;
+      default:
+        sections[index] = new ElfSection(*tmp_shdr[index], tmp_file, this);
+    }
+  }
+  return sections[index];
+}
+
+ElfSection* Elf::getSectionAt(unsigned int offset) {
+  for (int i = 1; i < ehdr->e_shnum; i++) {
+    ElfSection* section = getSection(i);
+    if ((section != nullptr) && (section->getFlags() & SHF_ALLOC) &&
+        !(section->getFlags() & SHF_TLS) && (offset >= section->getAddr()) &&
+        (offset < section->getAddr() + section->getSize()))
+      return section;
+  }
+  return nullptr;
+}
+
+ElfSegment* Elf::getSegmentByType(unsigned int type, ElfSegment* last) {
+  std::vector<ElfSegment*>::iterator seg;
+  if (last) {
+    seg = std::find(segments.begin(), segments.end(), last);
+    ++seg;
+  } else
+    seg = segments.begin();
+  for (; seg != segments.end(); seg++)
+    if ((*seg)->getType() == type) return *seg;
+  return nullptr;
+}
+
+void Elf::removeSegment(ElfSegment* segment) {
+  if (!segment) return;
+  std::vector<ElfSegment*>::iterator seg;
+  seg = std::find(segments.begin(), segments.end(), segment);
+  if (seg == segments.end()) return;
+  segment->clear();
+  segments.erase(seg);
+}
+
+ElfDynamic_Section* Elf::getDynSection() {
+  for (std::vector<ElfSegment*>::iterator seg = segments.begin();
+       seg != segments.end(); seg++)
+    if (((*seg)->getType() == PT_DYNAMIC) &&
+        ((*seg)->getFirstSection() != nullptr) &&
+        (*seg)->getFirstSection()->getType() == SHT_DYNAMIC)
+      return (ElfDynamic_Section*)(*seg)->getFirstSection();
+
+  return nullptr;
+}
+
+void Elf::normalize() {
+  // fixup section headers sh_name; TODO: that should be done by sections
+  // themselves
+  for (ElfSection* section = ehdr; section != nullptr;
+       section = section->getNext()) {
+    if (section->getIndex() == 0)
+      continue;
+    else
+      ehdr->e_shnum = section->getIndex() + 1;
+    section->getShdr().sh_name = eh_shstrndx->getStrIndex(section->getName());
+  }
+  ehdr->markDirty();
+  // Check segments consistency
+  int i = 0;
+  for (std::vector<ElfSegment*>::iterator seg = segments.begin();
+       seg != segments.end(); seg++, i++) {
+    std::list<ElfSection*>::iterator it = (*seg)->begin();
+    for (ElfSection* last = *(it++); it != (*seg)->end(); last = *(it++)) {
+      if (((*it)->getType() != SHT_NOBITS) &&
+          ((*it)->getAddr() - last->getAddr()) !=
+              ((*it)->getOffset() - last->getOffset())) {
+        throw std::runtime_error("Segments inconsistency");
+      }
+    }
+  }
+
+  ElfSegment* prevLoad = nullptr;
+  for (auto& it : segments) {
+    if (it->getType() == PT_LOAD) {
+      if (prevLoad) {
+        size_t alignedPrevEnd = (prevLoad->getAddr() + prevLoad->getMemSize() +
+                                 prevLoad->getAlign() - 1) &
+                                ~(prevLoad->getAlign() - 1);
+        size_t alignedStart = it->getAddr() & ~(it->getAlign() - 1);
+        if (alignedPrevEnd > alignedStart) {
+          throw std::runtime_error("Segments overlap");
+        }
+      }
+      prevLoad = it;
+    }
+  }
+
+  // fixup ehdr before writing
+  if (ehdr->e_phnum != segments.size()) {
+    ehdr->e_phnum = segments.size();
+    phdr_section->getShdr().sh_size =
+        segments.size() * Elf_Phdr::size(ehdr->e_ident[EI_CLASS]);
+    phdr_section->getNext()->markDirty();
+  }
+  // fixup shdr before writing
+  if (ehdr->e_shnum != shdr_section->getSize() / shdr_section->getEntSize())
+    shdr_section->getShdr().sh_size =
+        ehdr->e_shnum * Elf_Shdr::size(ehdr->e_ident[EI_CLASS]);
+  ehdr->e_shoff = shdr_section->getOffset();
+  ehdr->e_entry = eh_entry.getValue();
+  ehdr->e_shstrndx = eh_shstrndx->getIndex();
+
+  // Check sections consistency
+  unsigned int minOffset = 0;
+  for (ElfSection* section = ehdr; section != nullptr;
+       section = section->getNext()) {
+    unsigned int offset = section->getOffset();
+    if (offset < minOffset) {
+      throw std::runtime_error("Sections overlap");
+    }
+    if (section->getType() != SHT_NOBITS) {
+      minOffset = offset + section->getSize();
+    }
+  }
+}
+
+void Elf::write(std::ofstream& file) {
+  normalize();
+  for (ElfSection* section = ehdr; section != nullptr;
+       section = section->getNext()) {
+    file.seekp(section->getOffset());
+    if (section == phdr_section) {
+      for (std::vector<ElfSegment*>::iterator seg = segments.begin();
+           seg != segments.end(); seg++) {
+        Elf_Phdr phdr;
+        phdr.p_type = (*seg)->getType();
+        phdr.p_flags = (*seg)->getFlags();
+        phdr.p_offset = (*seg)->getOffset();
+        phdr.p_vaddr = (*seg)->getAddr();
+        phdr.p_paddr = phdr.p_vaddr + (*seg)->getVPDiff();
+        phdr.p_filesz = (*seg)->getFileSize();
+        phdr.p_memsz = (*seg)->getMemSize();
+        phdr.p_align = (*seg)->getAlign();
+        phdr.serialize(file, ehdr->e_ident[EI_CLASS], ehdr->e_ident[EI_DATA]);
+      }
+    } else if (section == shdr_section) {
+      null_section.serialize(file, ehdr->e_ident[EI_CLASS],
+                             ehdr->e_ident[EI_DATA]);
+      for (ElfSection* sec = ehdr; sec != nullptr; sec = sec->getNext()) {
+        if (sec->getType() != SHT_NULL)
+          sec->getShdr().serialize(file, ehdr->e_ident[EI_CLASS],
+                                   ehdr->e_ident[EI_DATA]);
+      }
+    } else
+      section->serialize(file, ehdr->e_ident[EI_CLASS], ehdr->e_ident[EI_DATA]);
+  }
+}
+
+ElfSection::ElfSection(Elf_Shdr& s, std::ifstream* file, Elf* parent)
+    : shdr(s),
+      link(shdr.sh_link == SHN_UNDEF ? nullptr
+                                     : parent->getSection(shdr.sh_link)),
+      next(nullptr),
+      previous(nullptr),
+      index(-1) {
+  if ((file == nullptr) || (shdr.sh_type == SHT_NULL) ||
+      (shdr.sh_type == SHT_NOBITS))
+    data = nullptr;
+  else {
+    data = static_cast<char*>(malloc(shdr.sh_size));
+    if (!data) {
+      throw std::runtime_error("Could not malloc ElfSection data");
+    }
+    auto pos = file->tellg();
+    file->seekg(shdr.sh_offset);
+    file->read(data, shdr.sh_size);
+    file->seekg(pos);
+  }
+  if (shdr.sh_name == 0)
+    name = nullptr;
+  else {
+    ElfStrtab_Section* strtab = (ElfStrtab_Section*)parent->getSection(-1);
+    // Special case (see elfgeneric.cpp): if strtab is nullptr, the
+    // section being created is the strtab.
+    if (strtab == nullptr)
+      name = &data[shdr.sh_name];
+    else
+      name = strtab->getStr(shdr.sh_name);
+  }
+  // Only SHT_REL/SHT_RELA sections use sh_info to store a section
+  // number.
+  if ((shdr.sh_type == SHT_REL) || (shdr.sh_type == SHT_RELA))
+    info.section = shdr.sh_info ? parent->getSection(shdr.sh_info) : nullptr;
+  else
+    info.index = shdr.sh_info;
+}
+
+unsigned int ElfSection::getAddr() {
+  if (shdr.sh_addr != (Elf64_Addr)-1) return shdr.sh_addr;
+
+  // It should be safe to adjust sh_addr for all allocated sections that
+  // are neither SHT_NOBITS nor SHT_PROGBITS
+  if ((previous != nullptr) && isRelocatable()) {
+    unsigned int addr = previous->getAddr();
+    if (previous->getType() != SHT_NOBITS) addr += previous->getSize();
+
+    if (addr & (getAddrAlign() - 1)) addr = (addr | (getAddrAlign() - 1)) + 1;
+
+    return (shdr.sh_addr = addr);
+  }
+  return shdr.sh_addr;
+}
+
+unsigned int ElfSection::getOffset() {
+  if (shdr.sh_offset != (Elf64_Off)-1) return shdr.sh_offset;
+
+  if (previous == nullptr) return (shdr.sh_offset = 0);
+
+  unsigned int offset = previous->getOffset();
+
+  ElfSegment* ptload = getSegmentByType(PT_LOAD);
+  ElfSegment* prev_ptload = previous->getSegmentByType(PT_LOAD);
+
+  if (ptload && (ptload == prev_ptload)) {
+    offset += getAddr() - previous->getAddr();
+    return (shdr.sh_offset = offset);
+  }
+
+  if (previous->getType() != SHT_NOBITS) offset += previous->getSize();
+
+  Elf32_Word align = 0x1000;
+  for (std::vector<ElfSegment*>::iterator seg = segments.begin();
+       seg != segments.end(); seg++)
+    align = std::max(align, (*seg)->getAlign());
+
+  Elf32_Word mask = align - 1;
+  // SHF_TLS is used for .tbss which is some kind of special case.
+  if (((getType() != SHT_NOBITS) || (getFlags() & SHF_TLS)) &&
+      (getFlags() & SHF_ALLOC)) {
+    if ((getAddr() & mask) < (offset & mask))
+      offset = (offset | mask) + (getAddr() & mask) + 1;
+    else
+      offset = (offset & ~mask) + (getAddr() & mask);
+  }
+  if ((getType() != SHT_NOBITS) && (offset & (getAddrAlign() - 1)))
+    offset = (offset | (getAddrAlign() - 1)) + 1;
+
+  return (shdr.sh_offset = offset);
+}
+
+int ElfSection::getIndex() {
+  if (index != -1) return index;
+  if (getType() == SHT_NULL) return (index = 0);
+  ElfSection* reference;
+  for (reference = previous;
+       (reference != nullptr) && (reference->getType() == SHT_NULL);
+       reference = reference->getPrevious())
+    ;
+  if (reference == nullptr) return (index = 1);
+  return (index = reference->getIndex() + 1);
+}
+
+Elf_Shdr& ElfSection::getShdr() {
+  getOffset();
+  if (shdr.sh_link == (Elf64_Word)-1)
+    shdr.sh_link = getLink() ? getLink()->getIndex() : 0;
+  if (shdr.sh_info == (Elf64_Word)-1)
+    shdr.sh_info = ((getType() == SHT_REL) || (getType() == SHT_RELA))
+                       ? (getInfo().section ? getInfo().section->getIndex() : 0)
+                       : getInfo().index;
+
+  return shdr;
+}
+
+ElfSegment::ElfSegment(Elf_Phdr* phdr)
+    : type(phdr->p_type),
+      v_p_diff(phdr->p_paddr - phdr->p_vaddr),
+      flags(phdr->p_flags),
+      align(phdr->p_align),
+      vaddr(phdr->p_vaddr),
+      filesz(phdr->p_filesz),
+      memsz(phdr->p_memsz) {}
+
+void ElfSegment::addSection(ElfSection* section) {
+  // Make sure all sections in PT_GNU_RELRO won't be moved by elfhack
+  assert(!((type == PT_GNU_RELRO) && (section->isRelocatable())));
+
+  // TODO: Check overlapping sections
+  std::list<ElfSection*>::iterator i;
+  for (i = sections.begin(); i != sections.end(); ++i)
+    if ((*i)->getAddr() > section->getAddr()) break;
+  sections.insert(i, section);
+  section->addToSegment(this);
+}
+
+void ElfSegment::removeSection(ElfSection* section) {
+  sections.remove(section);
+  section->removeFromSegment(this);
+}
+
+unsigned int ElfSegment::getFileSize() {
+  if (type == PT_GNU_RELRO) return filesz;
+
+  if (sections.empty()) return 0;
+  // Search the last section that is not SHT_NOBITS
+  std::list<ElfSection*>::reverse_iterator i;
+  for (i = sections.rbegin();
+       (i != sections.rend()) && ((*i)->getType() == SHT_NOBITS); ++i)
+    ;
+  // All sections are SHT_NOBITS
+  if (i == sections.rend()) return 0;
+
+  unsigned int end = (*i)->getAddr() + (*i)->getSize();
+
+  return end - sections.front()->getAddr();
+}
+
+unsigned int ElfSegment::getMemSize() {
+  if (type == PT_GNU_RELRO) return memsz;
+
+  if (sections.empty()) return 0;
+
+  unsigned int end = sections.back()->getAddr() + sections.back()->getSize();
+
+  return end - sections.front()->getAddr();
+}
+
+unsigned int ElfSegment::getOffset() {
+  if ((type == PT_GNU_RELRO) && !sections.empty() &&
+      (sections.front()->getAddr() != vaddr))
+    throw std::runtime_error(
+        "PT_GNU_RELRO segment doesn't start on a section start");
+
+  return sections.empty() ? 0 : sections.front()->getOffset();
+}
+
+unsigned int ElfSegment::getAddr() {
+  if ((type == PT_GNU_RELRO) && !sections.empty() &&
+      (sections.front()->getAddr() != vaddr))
+    throw std::runtime_error(
+        "PT_GNU_RELRO segment doesn't start on a section start");
+
+  return sections.empty() ? 0 : sections.front()->getAddr();
+}
+
+void ElfSegment::clear() {
+  for (std::list<ElfSection*>::iterator i = sections.begin();
+       i != sections.end(); ++i)
+    (*i)->removeFromSegment(this);
+  sections.clear();
+}
+
+ElfValue* ElfDynamic_Section::getValueForType(unsigned int tag) {
+  for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++)
+    if (dyns[i].tag == tag) return dyns[i].value;
+
+  return nullptr;
+}
+
+ElfSection* ElfDynamic_Section::getSectionForType(unsigned int tag) {
+  ElfValue* value = getValueForType(tag);
+  return value ? value->getSection() : nullptr;
+}
+
+bool ElfDynamic_Section::setValueForType(unsigned int tag, ElfValue* val) {
+  unsigned int i;
+  unsigned int shnum = shdr.sh_size / shdr.sh_entsize;
+  for (i = 0; (i < shnum) && (dyns[i].tag != DT_NULL); i++)
+    if (dyns[i].tag == tag) {
+      delete dyns[i].value;
+      dyns[i].value = val;
+      return true;
+    }
+  // If we get here, this means we didn't match for the given tag
+  // Most of the time, there are a few DT_NULL entries, that we can
+  // use to add our value, but if we are on the last entry, we can't.
+  if (i >= shnum - 1) return false;
+
+  dyns[i].tag = tag;
+  dyns[i].value = val;
+  return true;
+}
+
+ElfDynamic_Section::ElfDynamic_Section(Elf_Shdr& s, std::ifstream* file,
+                                       Elf* parent)
+    : ElfSection(s, file, parent) {
+  auto pos = file->tellg();
+  dyns.resize(s.sh_size / s.sh_entsize);
+  file->seekg(shdr.sh_offset);
+  // Here we assume tags refer to only one section (e.g. DT_RELSZ accounts
+  // for .rel.dyn size)
+  for (unsigned int i = 0; i < s.sh_size / s.sh_entsize; i++) {
+    Elf_Dyn dyn(*file, parent->getClass(), parent->getData());
+    dyns[i].tag = dyn.d_tag;
+    switch (dyn.d_tag) {
+      case DT_NULL:
+      case DT_SYMBOLIC:
+      case DT_TEXTREL:
+      case DT_BIND_NOW:
+        dyns[i].value = new ElfValue();
+        break;
+      case DT_NEEDED:
+      case DT_SONAME:
+      case DT_RPATH:
+      case DT_PLTREL:
+      case DT_RUNPATH:
+      case DT_FLAGS:
+      case DT_RELACOUNT:
+      case DT_RELCOUNT:
+      case DT_VERDEFNUM:
+      case DT_VERNEEDNUM:
+        dyns[i].value = new ElfPlainValue(dyn.d_un.d_val);
+        break;
+      case DT_PLTGOT:
+      case DT_HASH:
+      case DT_STRTAB:
+      case DT_SYMTAB:
+      case DT_RELA:
+      case DT_INIT:
+      case DT_FINI:
+      case DT_REL:
+      case DT_JMPREL:
+      case DT_INIT_ARRAY:
+      case DT_FINI_ARRAY:
+      case DT_GNU_HASH:
+      case DT_VERSYM:
+      case DT_VERNEED:
+      case DT_VERDEF:
+        dyns[i].value = new ElfLocation(dyn.d_un.d_ptr, parent);
+        break;
+      default:
+        dyns[i].value = nullptr;
+    }
+  }
+  // Another loop to get the section sizes
+  for (unsigned int i = 0; i < s.sh_size / s.sh_entsize; i++)
+    switch (dyns[i].tag) {
+      case DT_PLTRELSZ:
+        dyns[i].value = new ElfSize(getSectionForType(DT_JMPREL));
+        break;
+      case DT_RELASZ:
+        dyns[i].value = new ElfSize(getSectionForType(DT_RELA));
+        break;
+      case DT_STRSZ:
+        dyns[i].value = new ElfSize(getSectionForType(DT_STRTAB));
+        break;
+      case DT_RELSZ:
+        dyns[i].value = new ElfSize(getSectionForType(DT_REL));
+        break;
+      case DT_INIT_ARRAYSZ:
+        dyns[i].value = new ElfSize(getSectionForType(DT_INIT_ARRAY));
+        break;
+      case DT_FINI_ARRAYSZ:
+        dyns[i].value = new ElfSize(getSectionForType(DT_FINI_ARRAY));
+        break;
+      case DT_RELAENT:
+        dyns[i].value = new ElfEntSize(getSectionForType(DT_RELA));
+        break;
+      case DT_SYMENT:
+        dyns[i].value = new ElfEntSize(getSectionForType(DT_SYMTAB));
+        break;
+      case DT_RELENT:
+        dyns[i].value = new ElfEntSize(getSectionForType(DT_REL));
+        break;
+    }
+
+  file->seekg(pos);
+}
+
+ElfDynamic_Section::~ElfDynamic_Section() {
+  for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++)
+    delete dyns[i].value;
+}
+
+void ElfDynamic_Section::serialize(std::ofstream& file, unsigned char ei_class,
+                                   unsigned char ei_data) {
+  for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++) {
+    Elf_Dyn dyn;
+    dyn.d_tag = dyns[i].tag;
+    dyn.d_un.d_val = (dyns[i].value != nullptr) ? dyns[i].value->getValue() : 0;
+    dyn.serialize(file, ei_class, ei_data);
+  }
+}
+
+ElfSymtab_Section::ElfSymtab_Section(Elf_Shdr& s, std::ifstream* file,
+                                     Elf* parent)
+    : ElfSection(s, file, parent) {
+  auto pos = file->tellg();
+  syms.resize(s.sh_size / s.sh_entsize);
+  ElfStrtab_Section* strtab = (ElfStrtab_Section*)getLink();
+  file->seekg(shdr.sh_offset);
+  for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++) {
+    Elf_Sym sym(*file, parent->getClass(), parent->getData());
+    syms[i].name = strtab->getStr(sym.st_name);
+    syms[i].info = sym.st_info;
+    syms[i].other = sym.st_other;
+    ElfSection* section =
+        (sym.st_shndx == SHN_ABS) ? nullptr : parent->getSection(sym.st_shndx);
+    new (&syms[i].value)
+        ElfLocation(section, sym.st_value, ElfLocation::ABSOLUTE);
+    syms[i].size = sym.st_size;
+    syms[i].defined = (sym.st_shndx != SHN_UNDEF);
+  }
+  file->seekg(pos);
+}
+
+void ElfSymtab_Section::serialize(std::ofstream& file, unsigned char ei_class,
+                                  unsigned char ei_data) {
+  ElfStrtab_Section* strtab = (ElfStrtab_Section*)getLink();
+  for (unsigned int i = 0; i < shdr.sh_size / shdr.sh_entsize; i++) {
+    Elf_Sym sym;
+    sym.st_name = strtab->getStrIndex(syms[i].name);
+    sym.st_info = syms[i].info;
+    sym.st_other = syms[i].other;
+    sym.st_value = syms[i].value.getValue();
+    ElfSection* section = syms[i].value.getSection();
+    if (syms[i].defined)
+      sym.st_shndx = section ? section->getIndex() : SHN_ABS;
+    else
+      sym.st_shndx = SHN_UNDEF;
+    sym.st_size = syms[i].size;
+    sym.serialize(file, ei_class, ei_data);
+  }
+}
+
+Elf_SymValue* ElfSymtab_Section::lookup(const char* name,
+                                        unsigned int type_filter) {
+  for (std::vector<Elf_SymValue>::iterator sym = syms.begin();
+       sym != syms.end(); sym++) {
+    if ((type_filter & (1 << ELF32_ST_TYPE(sym->info))) &&
+        (strcmp(sym->name, name) == 0)) {
+      return &*sym;
+    }
+  }
+  return nullptr;
+}
+
+const char* ElfStrtab_Section::getStr(unsigned int index) {
+  for (std::vector<table_storage>::iterator t = table.begin(); t != table.end();
+       t++) {
+    if (index < t->used) return t->buf + index;
+    index -= t->used;
+  }
+  assert(1 == 0);
+  return nullptr;
+}
+
+const char* ElfStrtab_Section::getStr(const char* string) {
+  if (string == nullptr) return nullptr;
+
+  // If the given string is within the section, return it
+  for (std::vector<table_storage>::iterator t = table.begin(); t != table.end();
+       t++)
+    if ((string >= t->buf) && (string < t->buf + t->used)) return string;
+
+  // TODO: should scan in the section to find an existing string
+
+  // If not, we need to allocate the string in the section
+  size_t len = strlen(string) + 1;
+
+  if (table.back().size - table.back().used < len)
+    table.resize(table.size() + 1);
+
+  char* alloc_str = table.back().buf + table.back().used;
+  memcpy(alloc_str, string, len);
+  table.back().used += len;
+
+  shdr.sh_size += len;
+  markDirty();
+
+  return alloc_str;
+}
+
+unsigned int ElfStrtab_Section::getStrIndex(const char* string) {
+  if (string == nullptr) return 0;
+
+  unsigned int index = 0;
+  string = getStr(string);
+  for (std::vector<table_storage>::iterator t = table.begin(); t != table.end();
+       t++) {
+    if ((string >= t->buf) && (string < t->buf + t->used))
+      return index + (string - t->buf);
+    index += t->used;
+  }
+
+  assert(1 == 0);
+  return 0;
+}
+
+void ElfStrtab_Section::serialize(std::ofstream& file, unsigned char ei_class,
+                                  unsigned char ei_data) {
+  file.seekp(getOffset());
+  for (std::vector<table_storage>::iterator t = table.begin(); t != table.end();
+       t++)
+    file.write(t->buf, t->used);
+}
diff --git a/build/unix/elfhack/elfhack.cpp b/build/unix/elfhack/elfhack.cpp
new file mode 100644
index 0000000000..6771cffa6e
--- /dev/null
+++ b/build/unix/elfhack/elfhack.cpp
@@ -0,0 +1,1450 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#undef NDEBUG
+#include <assert.h>
+#include <cstring>
+#include <cstdlib>
+#include <cstdio>
+#include <memory>
+
+#include "elfxx.h"
+#include "mozilla/CheckedInt.h"
+
+#define ver "1"
+#define elfhack_data ".elfhack.data.v" ver
+#define elfhack_text ".elfhack.text.v" ver
+
+#ifndef R_ARM_V4BX
+#  define R_ARM_V4BX 0x28
+#endif
+#ifndef R_ARM_CALL
+#  define R_ARM_CALL 0x1c
+#endif
+#ifndef R_ARM_JUMP24
+#  define R_ARM_JUMP24 0x1d
+#endif
+#ifndef R_ARM_THM_JUMP24
+#  define R_ARM_THM_JUMP24 0x1e
+#endif
+
+char* rundir = nullptr;
+
+template <typename T>
+struct wrapped {
+  T value;
+};
+
+class Elf_Addr_Traits {
+ public:
+  typedef wrapped<Elf32_Addr> Type32;
+  typedef wrapped<Elf64_Addr> Type64;
+
+  template <class endian, typename R, typename T>
+  static inline void swap(T& t, R& r) {
+    r.value = endian::swap(t.value);
+  }
+};
+
+typedef serializable<Elf_Addr_Traits> Elf_Addr;
+
+class ElfRelHack_Section : public ElfSection {
+ public:
+  ElfRelHack_Section(Elf_Shdr& s)
+      : ElfSection(s, nullptr, nullptr),
+        block_size((8 * s.sh_entsize - 1) * s.sh_entsize) {
+    name = elfhack_data;
+  };
+
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data) {
+    for (std::vector<Elf64_Addr>::iterator i = relr.begin(); i != relr.end();
+         ++i) {
+      Elf_Addr out;
+      out.value = *i;
+      out.serialize(file, ei_class, ei_data);
+    }
+  }
+
+  bool isRelocatable() { return true; }
+
+  void push_back(Elf64_Addr offset) {
+    // The format used for the packed relocations is SHT_RELR, described in
+    // https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/Jnz1lgLJAgAJ
+    // The gist of it is that an address is recorded, and the following words,
+    // if their LSB is 1, represent a bitmap of word-size-spaced relocations
+    // at the addresses that follow. There can be multiple such bitmaps, such
+    // that very long streaks of (possibly spaced) relocations can be recorded
+    // in a very compact way.
+    for (;;) {
+      // [block_start; block_start + block_size] represents the range of offsets
+      // the current bitmap can record. If the offset doesn't fall in that
+      // range, or if doesn't align properly to be recorded, we record the
+      // bitmap, and slide the block corresponding to a new bitmap. If the
+      // offset doesn't fall in the range for the new bitmap, or if there wasn't
+      // an active bitmap in the first place, we record the offset and start a
+      // new bitmap for the block that follows it.
+      if (!block_start || offset < block_start ||
+          offset >= block_start + block_size ||
+          (offset - block_start) % shdr.sh_entsize) {
+        if (bitmap) {
+          relr.push_back((bitmap << 1) | 1);
+          block_start += block_size;
+          bitmap = 0;
+          continue;
+        }
+        relr.push_back(offset);
+        block_start = offset + shdr.sh_entsize;
+        break;
+      }
+      bitmap |= 1ULL << ((offset - block_start) / shdr.sh_entsize);
+      break;
+    }
+    shdr.sh_size = relr.size() * shdr.sh_entsize;
+  }
+
+ private:
+  std::vector<Elf64_Addr> relr;
+  size_t block_size;
+  Elf64_Addr block_start = 0;
+  Elf64_Addr bitmap = 0;
+};
+
+class ElfRelHackCode_Section : public ElfSection {
+ public:
+  ElfRelHackCode_Section(Elf_Shdr& s, Elf& e,
+                         ElfRelHack_Section& relhack_section, unsigned int init,
+                         unsigned int mprotect_cb, unsigned int sysconf_cb)
+      : ElfSection(s, nullptr, nullptr),
+        parent(e),
+        relhack_section(relhack_section),
+        init(init),
+        init_trampoline(nullptr),
+        mprotect_cb(mprotect_cb),
+        sysconf_cb(sysconf_cb) {
+    std::string file(rundir);
+    file += "/inject/";
+    switch (parent.getMachine()) {
+      case EM_386:
+        file += "x86";
+        break;
+      case EM_X86_64:
+        file += "x86_64";
+        break;
+      case EM_ARM:
+        file += "arm";
+        break;
+      case EM_AARCH64:
+        file += "aarch64";
+        break;
+      default:
+        throw std::runtime_error("unsupported architecture");
+    }
+    file += ".o";
+    std::ifstream inject(file.c_str(), std::ios::in | std::ios::binary);
+    elf = new Elf(inject);
+    if (elf->getType() != ET_REL)
+      throw std::runtime_error("object for injected code is not ET_REL");
+    if (elf->getMachine() != parent.getMachine())
+      throw std::runtime_error(
+          "architecture of object for injected code doesn't match");
+
+    ElfSymtab_Section* symtab = nullptr;
+
+    // Find the symbol table.
+    for (ElfSection* section = elf->getSection(1); section != nullptr;
+         section = section->getNext()) {
+      if (section->getType() == SHT_SYMTAB)
+        symtab = (ElfSymtab_Section*)section;
+    }
+    if (symtab == nullptr)
+      throw std::runtime_error(
+          "Couldn't find a symbol table for the injected code");
+
+    relro = parent.getSegmentByType(PT_GNU_RELRO);
+
+    // Find the init symbol
+    entry_point = -1;
+    std::string symbol = "init";
+    if (!init) symbol += "_noinit";
+    if (relro) symbol += "_relro";
+    Elf_SymValue* sym = symtab->lookup(symbol.c_str());
+    if (!sym)
+      throw std::runtime_error(
+          "Couldn't find an 'init' symbol in the injected code");
+
+    entry_point = sym->value.getValue();
+
+    // Get all relevant sections from the injected code object.
+    add_code_section(sym->value.getSection());
+
+    // If the original init function is located too far away, we're going to
+    // need to use a trampoline. See comment in inject.c.
+    // Theoretically, we should check for (init - instr) > 0xffffff, where instr
+    // is the virtual address of the instruction that calls the original init,
+    // but we don't have it at this point, so punt to just init.
+    if (init > 0xffffff && parent.getMachine() == EM_ARM) {
+      Elf_SymValue* trampoline = symtab->lookup("init_trampoline");
+      if (!trampoline) {
+        throw std::runtime_error(
+            "Couldn't find an 'init_trampoline' symbol in the injected code");
+      }
+
+      init_trampoline = trampoline->value.getSection();
+      add_code_section(init_trampoline);
+    }
+
+    // Adjust code sections offsets according to their size
+    std::vector<ElfSection*>::iterator c = code.begin();
+    (*c)->getShdr().sh_addr = 0;
+    for (ElfSection* last = *(c++); c != code.end(); ++c) {
+      unsigned int addr = last->getShdr().sh_addr + last->getSize();
+      if (addr & ((*c)->getAddrAlign() - 1))
+        addr = (addr | ((*c)->getAddrAlign() - 1)) + 1;
+      (*c)->getShdr().sh_addr = addr;
+      // We need to align this section depending on the greater
+      // alignment required by code sections.
+      if (shdr.sh_addralign < (*c)->getAddrAlign())
+        shdr.sh_addralign = (*c)->getAddrAlign();
+      last = *c;
+    }
+    shdr.sh_size = code.back()->getAddr() + code.back()->getSize();
+    data = static_cast<char*>(malloc(shdr.sh_size));
+    if (!data) {
+      throw std::runtime_error("Could not malloc ElfSection data");
+    }
+    char* buf = data;
+    for (c = code.begin(); c != code.end(); ++c) {
+      memcpy(buf, (*c)->getData(), (*c)->getSize());
+      buf += (*c)->getSize();
+    }
+    name = elfhack_text;
+  }
+
+  ~ElfRelHackCode_Section() { delete elf; }
+
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data) override {
+    // Readjust code offsets
+    for (std::vector<ElfSection*>::iterator c = code.begin(); c != code.end();
+         ++c)
+      (*c)->getShdr().sh_addr += getAddr();
+
+    // Apply relocations
+    for (std::vector<ElfSection*>::iterator c = code.begin(); c != code.end();
+         ++c) {
+      for (ElfSection* rel = elf->getSection(1); rel != nullptr;
+           rel = rel->getNext())
+        if (((rel->getType() == SHT_REL) || (rel->getType() == SHT_RELA)) &&
+            (rel->getInfo().section == *c)) {
+          if (rel->getType() == SHT_REL)
+            apply_relocations((ElfRel_Section<Elf_Rel>*)rel, *c);
+          else
+            apply_relocations((ElfRel_Section<Elf_Rela>*)rel, *c);
+        }
+    }
+
+    ElfSection::serialize(file, ei_class, ei_data);
+  }
+
+  bool isRelocatable() override { return false; }
+
+  unsigned int getEntryPoint() { return entry_point; }
+
+  void insertBefore(ElfSection* section, bool dirty = true) override {
+    // Adjust the address so that this section is adjacent to the one it's
+    // being inserted before. This avoids creating holes which subsequently
+    // might lead the PHDR-adjusting code to create unnecessary additional
+    // PT_LOADs.
+    shdr.sh_addr =
+        (section->getAddr() - shdr.sh_size) & ~(shdr.sh_addralign - 1);
+    ElfSection::insertBefore(section, dirty);
+  }
+
+ private:
+  void add_code_section(ElfSection* section) {
+    if (section) {
+      /* Don't add section if it's already been added in the past */
+      for (auto s = code.begin(); s != code.end(); ++s) {
+        if (section == *s) return;
+      }
+      code.push_back(section);
+      find_code(section);
+    }
+  }
+
+  /* Look at the relocations associated to the given section to find other
+   * sections that it requires */
+  void find_code(ElfSection* section) {
+    for (ElfSection* s = elf->getSection(1); s != nullptr; s = s->getNext()) {
+      if (((s->getType() == SHT_REL) || (s->getType() == SHT_RELA)) &&
+          (s->getInfo().section == section)) {
+        if (s->getType() == SHT_REL)
+          scan_relocs_for_code((ElfRel_Section<Elf_Rel>*)s);
+        else
+          scan_relocs_for_code((ElfRel_Section<Elf_Rela>*)s);
+      }
+    }
+  }
+
+  template <typename Rel_Type>
+  void scan_relocs_for_code(ElfRel_Section<Rel_Type>* rel) {
+    ElfSymtab_Section* symtab = (ElfSymtab_Section*)rel->getLink();
+    for (auto r = rel->rels.begin(); r != rel->rels.end(); ++r) {
+      ElfSection* section =
+          symtab->syms[ELF64_R_SYM(r->r_info)].value.getSection();
+      add_code_section(section);
+    }
+  }
+
+  // TODO: sort out which non-aarch64 relocation types should be using
+  //  `value` (even though in practice it's either 0 or the same as addend)
+  class pc32_relocation {
+   public:
+    Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
+                          Elf64_Sxword addend, unsigned int addr,
+                          Elf64_Word value) {
+      return addr + addend - offset - base_addr;
+    }
+  };
+
+  class arm_plt32_relocation {
+   public:
+    Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
+                          Elf64_Sxword addend, unsigned int addr,
+                          Elf64_Word value) {
+      // We don't care about sign_extend because the only case where this is
+      // going to be used only jumps forward.
+      Elf32_Addr tmp = (Elf32_Addr)(addr - offset - base_addr) >> 2;
+      tmp = (addend + tmp) & 0x00ffffff;
+      return (addend & 0xff000000) | tmp;
+    }
+  };
+
+  class arm_thm_jump24_relocation {
+   public:
+    Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
+                          Elf64_Sxword addend, unsigned int addr,
+                          Elf64_Word value) {
+      /* Follows description of b.w and bl instructions as per
+         ARM Architecture Reference Manual ARM® v7-A and ARM® v7-R edition,
+         A8.6.16 We limit ourselves to Encoding T4 of b.w and Encoding T1 of bl.
+         We don't care about sign_extend because the only case where this is
+         going to be used only jumps forward. */
+      Elf32_Addr tmp = (Elf32_Addr)(addr - offset - base_addr);
+      unsigned int word0 = addend & 0xffff, word1 = addend >> 16;
+
+      /* Encoding T4 of B.W is 10x1 ; Encoding T1 of BL is 11x1. */
+      unsigned int type = (word1 & 0xd000) >> 12;
+      if (((word0 & 0xf800) != 0xf000) || ((type & 0x9) != 0x9))
+        throw std::runtime_error(
+            "R_ARM_THM_JUMP24/R_ARM_THM_CALL relocation only supported for B.W "
+            "<label> and BL <label>");
+
+      /* When the target address points to ARM code, switch a BL to a
+       * BLX. This however can't be done with a B.W without adding a
+       * trampoline, which is not supported as of now. */
+      if ((addr & 0x1) == 0) {
+        if (type == 0x9)
+          throw std::runtime_error(
+              "R_ARM_THM_JUMP24/R_ARM_THM_CALL relocation only supported for "
+              "BL <label> when label points to ARM code");
+        /* The address of the target is always relative to a 4-bytes
+         * aligned address, so if the address of the BL instruction is
+         * not 4-bytes aligned, adjust for it. */
+        if ((base_addr + offset) & 0x2) tmp += 2;
+        /* Encoding T2 of BLX is 11x0. */
+        type = 0xc;
+      }
+
+      unsigned int s = (word0 & (1 << 10)) >> 10;
+      unsigned int j1 = (word1 & (1 << 13)) >> 13;
+      unsigned int j2 = (word1 & (1 << 11)) >> 11;
+      unsigned int i1 = j1 ^ s ? 0 : 1;
+      unsigned int i2 = j2 ^ s ? 0 : 1;
+
+      tmp += ((s << 24) | (i1 << 23) | (i2 << 22) | ((word0 & 0x3ff) << 12) |
+              ((word1 & 0x7ff) << 1));
+
+      s = (tmp & (1 << 24)) >> 24;
+      j1 = ((tmp & (1 << 23)) >> 23) ^ !s;
+      j2 = ((tmp & (1 << 22)) >> 22) ^ !s;
+
+      return 0xf000 | (s << 10) | ((tmp & (0x3ff << 12)) >> 12) | (type << 28) |
+             (j1 << 29) | (j2 << 27) | ((tmp & 0xffe) << 15);
+    }
+  };
+
+  class gotoff_relocation {
+   public:
+    Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
+                          Elf64_Sxword addend, unsigned int addr,
+                          Elf64_Word value) {
+      return addr + addend;
+    }
+  };
+
+  template <int start, int end>
+  class abs_lo12_nc_relocation {
+   public:
+    Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
+                          Elf64_Sxword addend, unsigned int addr,
+                          Elf64_Word value) {
+      // Fill the bits [end:start] of the immediate value in an ADD, LDR or STR
+      // instruction, at bits [21:10].
+      // per ARM® Architecture Reference Manual ARMv8, for ARMv8-A architecture
+      // profile C5.6.4, C5.6.83 or C5.6.178 and ELF for the ARM® 64-bit
+      // Architecture (AArch64) 4.6.6, Table 4-9.
+      Elf64_Word mask = (1 << (end + 1)) - 1;
+      return value | (((((addr + addend) & mask) >> start) & 0xfff) << 10);
+    }
+  };
+
+  class adr_prel_pg_hi21_relocation {
+   public:
+    Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
+                          Elf64_Sxword addend, unsigned int addr,
+                          Elf64_Word value) {
+      // Fill the bits [32:12] of the immediate value in a ADRP instruction,
+      // at bits [23:5]+[30:29].
+      // per ARM® Architecture Reference Manual ARMv8, for ARMv8-A architecture
+      // profile C5.6.10 and ELF for the ARM® 64-bit Architecture
+      // (AArch64) 4.6.6, Table 4-9.
+      Elf64_Word imm = ((addr + addend) >> 12) - ((base_addr + offset) >> 12);
+      Elf64_Word immLo = (imm & 0x3) << 29;
+      Elf64_Word immHi = (imm & 0x1ffffc) << 3;
+      return value & 0x9f00001f | immLo | immHi;
+    }
+  };
+
+  class call26_relocation {
+   public:
+    Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
+                          Elf64_Sxword addend, unsigned int addr,
+                          Elf64_Word value) {
+      // Fill the bits [27:2] of the immediate value in a BL instruction,
+      // at bits [25:0].
+      // per ARM® Architecture Reference Manual ARMv8, for ARMv8-A architecture
+      // profile C5.6.26 and ELF for the ARM® 64-bit Architecture
+      // (AArch64) 4.6.6, Table 4-10.
+      return value | (((addr + addend - offset - base_addr) & 0x0ffffffc) >> 2);
+    }
+  };
+
+  template <class relocation_type>
+  void apply_relocation(ElfSection* the_code, char* base, Elf_Rel* r,
+                        unsigned int addr) {
+    relocation_type relocation;
+    Elf32_Addr value;
+    memcpy(&value, base + r->r_offset, 4);
+    value = relocation(the_code->getAddr(), r->r_offset, value, addr, value);
+    memcpy(base + r->r_offset, &value, 4);
+  }
+
+  template <class relocation_type>
+  void apply_relocation(ElfSection* the_code, char* base, Elf_Rela* r,
+                        unsigned int addr) {
+    relocation_type relocation;
+    Elf64_Word value;
+    memcpy(&value, base + r->r_offset, 4);
+    Elf32_Addr new_value =
+        relocation(the_code->getAddr(), r->r_offset, r->r_addend, addr, value);
+    memcpy(base + r->r_offset, &new_value, 4);
+  }
+
+  template <typename Rel_Type>
+  void apply_relocations(ElfRel_Section<Rel_Type>* rel, ElfSection* the_code) {
+    assert(rel->getType() == Rel_Type::sh_type);
+    char* buf = data + (the_code->getAddr() - code.front()->getAddr());
+    // TODO: various checks on the sections
+    ElfSymtab_Section* symtab = (ElfSymtab_Section*)rel->getLink();
+    for (typename std::vector<Rel_Type>::iterator r = rel->rels.begin();
+         r != rel->rels.end(); ++r) {
+      // TODO: various checks on the symbol
+      const char* name = symtab->syms[ELF64_R_SYM(r->r_info)].name;
+      unsigned int addr;
+      if (symtab->syms[ELF64_R_SYM(r->r_info)].value.getSection() == nullptr) {
+        if (strcmp(name, "relhack") == 0) {
+          addr = relhack_section.getAddr();
+        } else if (strcmp(name, "elf_header") == 0) {
+          // TODO: change this ungly hack to something better
+          ElfSection* ehdr = parent.getSection(1)->getPrevious()->getPrevious();
+          addr = ehdr->getAddr();
+        } else if (strcmp(name, "original_init") == 0) {
+          if (init_trampoline) {
+            addr = init_trampoline->getAddr();
+          } else {
+            addr = init;
+          }
+        } else if (strcmp(name, "real_original_init") == 0) {
+          addr = init;
+        } else if (relro && strcmp(name, "mprotect_cb") == 0) {
+          addr = mprotect_cb;
+        } else if (relro && strcmp(name, "sysconf_cb") == 0) {
+          addr = sysconf_cb;
+        } else if (relro && strcmp(name, "relro_start") == 0) {
+          addr = relro->getAddr();
+        } else if (relro && strcmp(name, "relro_end") == 0) {
+          addr = (relro->getAddr() + relro->getMemSize());
+        } else if (strcmp(name, "_GLOBAL_OFFSET_TABLE_") == 0) {
+          // We actually don't need a GOT, but need it as a reference for
+          // GOTOFF relocations. We'll just use the start of the ELF file
+          addr = 0;
+        } else if (strcmp(name, "") == 0) {
+          // This is for R_ARM_V4BX, until we find something better
+          addr = -1;
+        } else {
+          throw std::runtime_error("Unsupported symbol in relocation");
+        }
+      } else {
+        ElfSection* section =
+            symtab->syms[ELF64_R_SYM(r->r_info)].value.getSection();
+        assert((section->getType() == SHT_PROGBITS) &&
+               (section->getFlags() & SHF_EXECINSTR));
+        addr = symtab->syms[ELF64_R_SYM(r->r_info)].value.getValue();
+      }
+      // Do the relocation
+#define REL(machine, type) (EM_##machine | (R_##machine##_##type << 8))
+      switch (elf->getMachine() | (ELF64_R_TYPE(r->r_info) << 8)) {
+        case REL(X86_64, PC32):
+        case REL(X86_64, PLT32):
+        case REL(386, PC32):
+        case REL(386, GOTPC):
+        case REL(ARM, GOTPC):
+        case REL(ARM, REL32):
+        case REL(AARCH64, PREL32):
+          apply_relocation<pc32_relocation>(the_code, buf, &*r, addr);
+          break;
+        case REL(ARM, CALL):
+        case REL(ARM, JUMP24):
+        case REL(ARM, PLT32):
+          apply_relocation<arm_plt32_relocation>(the_code, buf, &*r, addr);
+          break;
+        case REL(ARM, THM_PC22 /* THM_CALL */):
+        case REL(ARM, THM_JUMP24):
+          apply_relocation<arm_thm_jump24_relocation>(the_code, buf, &*r, addr);
+          break;
+        case REL(386, GOTOFF):
+        case REL(ARM, GOTOFF):
+          apply_relocation<gotoff_relocation>(the_code, buf, &*r, addr);
+          break;
+        case REL(AARCH64, ADD_ABS_LO12_NC):
+          apply_relocation<abs_lo12_nc_relocation<0, 11>>(the_code, buf, &*r,
+                                                          addr);
+          break;
+        case REL(AARCH64, ADR_PREL_PG_HI21):
+          apply_relocation<adr_prel_pg_hi21_relocation>(the_code, buf, &*r,
+                                                        addr);
+          break;
+        case REL(AARCH64, LDST32_ABS_LO12_NC):
+          apply_relocation<abs_lo12_nc_relocation<2, 11>>(the_code, buf, &*r,
+                                                          addr);
+          break;
+        case REL(AARCH64, LDST64_ABS_LO12_NC):
+          apply_relocation<abs_lo12_nc_relocation<3, 11>>(the_code, buf, &*r,
+                                                          addr);
+          break;
+        case REL(AARCH64, CALL26):
+          apply_relocation<call26_relocation>(the_code, buf, &*r, addr);
+          break;
+        case REL(ARM, V4BX):
+          // Ignore R_ARM_V4BX relocations
+          break;
+        default:
+          throw std::runtime_error("Unsupported relocation type");
+      }
+    }
+  }
+
+  Elf *elf, &parent;
+  ElfRelHack_Section& relhack_section;
+  std::vector<ElfSection*> code;
+  unsigned int init;
+  ElfSection* init_trampoline;
+  unsigned int mprotect_cb;
+  unsigned int sysconf_cb;
+  int entry_point;
+  ElfSegment* relro;
+};
+
+unsigned int get_addend(Elf_Rel* rel, Elf* elf) {
+  ElfLocation loc(rel->r_offset, elf);
+  Elf_Addr addr(loc.getBuffer(), Elf_Addr::size(elf->getClass()),
+                elf->getClass(), elf->getData());
+  return addr.value;
+}
+
+unsigned int get_addend(Elf_Rela* rel, Elf* elf) { return rel->r_addend; }
+
+void set_relative_reloc(Elf_Rel* rel, Elf* elf, unsigned int value) {
+  ElfLocation loc(rel->r_offset, elf);
+  Elf_Addr addr;
+  addr.value = value;
+  addr.serialize(const_cast<char*>(loc.getBuffer()),
+                 Elf_Addr::size(elf->getClass()), elf->getClass(),
+                 elf->getData());
+}
+
+void set_relative_reloc(Elf_Rela* rel, Elf* elf, unsigned int value) {
+  // ld puts the value of relocated relocations both in the addend and
+  // at r_offset. For consistency, keep it that way.
+  set_relative_reloc((Elf_Rel*)rel, elf, value);
+  rel->r_addend = value;
+}
+
+void maybe_split_segment(Elf* elf, ElfSegment* segment) {
+  std::list<ElfSection*>::iterator it = segment->begin();
+  for (ElfSection* last = *(it++); it != segment->end(); last = *(it++)) {
+    // When two consecutive non-SHT_NOBITS sections are apart by more
+    // than the alignment of the section, the second can be moved closer
+    // to the first, but this requires the segment to be split.
+    if (((*it)->getType() != SHT_NOBITS) && (last->getType() != SHT_NOBITS) &&
+        ((*it)->getOffset() - last->getOffset() - last->getSize() >
+         segment->getAlign())) {
+      // Probably very wrong.
+      Elf_Phdr phdr;
+      phdr.p_type = PT_LOAD;
+      phdr.p_vaddr = 0;
+      phdr.p_paddr = phdr.p_vaddr + segment->getVPDiff();
+      phdr.p_flags = segment->getFlags();
+      phdr.p_align = segment->getAlign();
+      phdr.p_filesz = (Elf64_Xword)-1LL;
+      phdr.p_memsz = (Elf64_Xword)-1LL;
+      ElfSegment* newSegment = new ElfSegment(&phdr);
+      elf->insertSegmentAfter(segment, newSegment);
+      for (; it != segment->end(); ++it) {
+        newSegment->addSection(*it);
+      }
+      for (it = newSegment->begin(); it != newSegment->end(); ++it) {
+        segment->removeSection(*it);
+      }
+      break;
+    }
+  }
+}
+
+// EH_FRAME constants
+static const unsigned char DW_EH_PE_absptr = 0x00;
+static const unsigned char DW_EH_PE_omit = 0xff;
+
+// Data size
+static const unsigned char DW_EH_PE_LEB128 = 0x01;
+static const unsigned char DW_EH_PE_data2 = 0x02;
+static const unsigned char DW_EH_PE_data4 = 0x03;
+static const unsigned char DW_EH_PE_data8 = 0x04;
+
+// Data signedness
+static const unsigned char DW_EH_PE_signed = 0x08;
+
+// Modifiers
+static const unsigned char DW_EH_PE_pcrel = 0x10;
+
+// Return the data size part of the encoding value
+static unsigned char encoding_data_size(unsigned char encoding) {
+  return encoding & 0x07;
+}
+
+// Advance `step` bytes in the buffer at `data` with size `size`, returning
+// the advanced buffer pointer and remaining size.
+// Returns true if step <= size.
+static bool advance_buffer(char** data, size_t* size, size_t step) {
+  if (step > *size) return false;
+
+  *data += step;
+  *size -= step;
+  return true;
+}
+
+// Advance in the given buffer, skipping the full length of the variable-length
+// encoded LEB128 type in CIE/FDE data.
+static bool skip_LEB128(char** data, size_t* size) {
+  if (!*size) return false;
+
+  while (*size && (*(*data)++ & (char)0x80)) {
+    (*size)--;
+  }
+  return true;
+}
+
+// Advance in the given buffer, skipping the full length of a pointer encoded
+// with the given encoding.
+static bool skip_eh_frame_pointer(char** data, size_t* size,
+                                  unsigned char encoding) {
+  switch (encoding_data_size(encoding)) {
+    case DW_EH_PE_data2:
+      return advance_buffer(data, size, 2);
+    case DW_EH_PE_data4:
+      return advance_buffer(data, size, 4);
+    case DW_EH_PE_data8:
+      return advance_buffer(data, size, 8);
+    case DW_EH_PE_LEB128:
+      return skip_LEB128(data, size);
+  }
+  throw std::runtime_error("unreachable");
+}
+
+// Specialized implementations for adjust_eh_frame_pointer().
+template <typename T>
+static bool adjust_eh_frame_sized_pointer(char** data, size_t* size,
+                                          ElfSection* eh_frame,
+                                          unsigned int origAddr, Elf* elf) {
+  if (*size < sizeof(T)) return false;
+
+  serializable<FixedSizeData<T>> pointer(*data, *size, elf->getClass(),
+                                         elf->getData());
+  mozilla::CheckedInt<T> value = pointer.value;
+  if (origAddr < eh_frame->getAddr()) {
+    unsigned int diff = eh_frame->getAddr() - origAddr;
+    value -= diff;
+  } else {
+    unsigned int diff = origAddr - eh_frame->getAddr();
+    value += diff;
+  }
+  if (!value.isValid())
+    throw std::runtime_error("Overflow while adjusting eh_frame");
+  pointer.value = value.value();
+  pointer.serialize(*data, *size, elf->getClass(), elf->getData());
+  return advance_buffer(data, size, sizeof(T));
+}
+
+// In the given eh_frame section, adjust the pointer with the given encoding,
+// pointed to by the given buffer (`data`, `size`), considering the eh_frame
+// section was originally at `origAddr`. Also advances in the buffer.
+static bool adjust_eh_frame_pointer(char** data, size_t* size,
+                                    unsigned char encoding,
+                                    ElfSection* eh_frame, unsigned int origAddr,
+                                    Elf* elf) {
+  if ((encoding & 0x70) != DW_EH_PE_pcrel)
+    return skip_eh_frame_pointer(data, size, encoding);
+
+  if (encoding & DW_EH_PE_signed) {
+    switch (encoding_data_size(encoding)) {
+      case DW_EH_PE_data2:
+        return adjust_eh_frame_sized_pointer<int16_t>(data, size, eh_frame,
+                                                      origAddr, elf);
+      case DW_EH_PE_data4:
+        return adjust_eh_frame_sized_pointer<int32_t>(data, size, eh_frame,
+                                                      origAddr, elf);
+      case DW_EH_PE_data8:
+        return adjust_eh_frame_sized_pointer<int64_t>(data, size, eh_frame,
+                                                      origAddr, elf);
+    }
+  } else {
+    switch (encoding_data_size(encoding)) {
+      case DW_EH_PE_data2:
+        return adjust_eh_frame_sized_pointer<uint16_t>(data, size, eh_frame,
+                                                       origAddr, elf);
+      case DW_EH_PE_data4:
+        return adjust_eh_frame_sized_pointer<uint32_t>(data, size, eh_frame,
+                                                       origAddr, elf);
+      case DW_EH_PE_data8:
+        return adjust_eh_frame_sized_pointer<uint64_t>(data, size, eh_frame,
+                                                       origAddr, elf);
+    }
+  }
+
+  throw std::runtime_error("Unsupported eh_frame pointer encoding");
+}
+
+// The eh_frame section may contain "PC"-relative pointers. If we move the
+// section, those need to be adjusted. Other type of pointers are relative to
+// sections we don't touch.
+static void adjust_eh_frame(ElfSection* eh_frame, unsigned int origAddr,
+                            Elf* elf) {
+  if (eh_frame->getAddr() == origAddr)  // nothing to do;
+    return;
+
+  char* data = const_cast<char*>(eh_frame->getData());
+  size_t size = eh_frame->getSize();
+  unsigned char LSDAencoding = DW_EH_PE_omit;
+  unsigned char FDEencoding = DW_EH_PE_absptr;
+  bool hasZ = false;
+
+  // Decoding of eh_frame based on https://www.airs.com/blog/archives/460
+  while (size) {
+    if (size < sizeof(uint32_t)) goto malformed;
+
+    serializable<FixedSizeData<uint32_t>> entryLength(
+        data, size, elf->getClass(), elf->getData());
+    if (!advance_buffer(&data, &size, sizeof(uint32_t))) goto malformed;
+
+    char* cursor = data;
+    size_t length = entryLength.value;
+
+    if (length == 0) {
+      continue;
+    }
+
+    if (size < sizeof(uint32_t)) goto malformed;
+
+    serializable<FixedSizeData<uint32_t>> id(data, size, elf->getClass(),
+                                             elf->getData());
+    if (!advance_buffer(&cursor, &length, sizeof(uint32_t))) goto malformed;
+
+    if (id.value == 0) {
+      // This is a Common Information Entry
+      if (length < 2) goto malformed;
+      // Reset LSDA and FDE encodings, and hasZ for subsequent FDEs.
+      LSDAencoding = DW_EH_PE_omit;
+      FDEencoding = DW_EH_PE_absptr;
+      hasZ = false;
+      // CIE version. Should only be 1 or 3.
+      char version = *cursor++;
+      length--;
+      if (version != 1 && version != 3) {
+        throw std::runtime_error("Unsupported eh_frame version");
+      }
+      // NUL terminated string.
+      const char* augmentationString = cursor;
+      size_t l = strnlen(augmentationString, length - 1);
+      if (l == length - 1) goto malformed;
+      if (!advance_buffer(&cursor, &length, l + 1)) goto malformed;
+      // Skip code alignment factor (LEB128)
+      if (!skip_LEB128(&cursor, &length)) goto malformed;
+      // Skip data alignment factor (LEB128)
+      if (!skip_LEB128(&cursor, &length)) goto malformed;
+      // Skip return address register (single byte in CIE version 1, LEB128
+      // in CIE version 3)
+      if (version == 1) {
+        if (!advance_buffer(&cursor, &length, 1)) goto malformed;
+      } else {
+        if (!skip_LEB128(&cursor, &length)) goto malformed;
+      }
+      // Past this, it's data driven by the contents of the augmentation string.
+      for (size_t i = 0; i < l; i++) {
+        if (!length) goto malformed;
+        switch (augmentationString[i]) {
+          case 'z':
+            if (!skip_LEB128(&cursor, &length)) goto malformed;
+            hasZ = true;
+            break;
+          case 'L':
+            LSDAencoding = *cursor++;
+            length--;
+            break;
+          case 'R':
+            FDEencoding = *cursor++;
+            length--;
+            break;
+          case 'P': {
+            unsigned char encoding = (unsigned char)*cursor++;
+            length--;
+            if (!adjust_eh_frame_pointer(&cursor, &length, encoding, eh_frame,
+                                         origAddr, elf))
+              goto malformed;
+          } break;
+          default:
+            goto malformed;
+        }
+      }
+    } else {
+      // This is a Frame Description Entry
+      // Starting address
+      if (!adjust_eh_frame_pointer(&cursor, &length, FDEencoding, eh_frame,
+                                   origAddr, elf))
+        goto malformed;
+
+      if (LSDAencoding != DW_EH_PE_omit) {
+        // Skip number of bytes, same size as the starting address.
+        if (!skip_eh_frame_pointer(&cursor, &length, FDEencoding))
+          goto malformed;
+        if (hasZ) {
+          if (!skip_LEB128(&cursor, &length)) goto malformed;
+        }
+        // pointer to the LSDA.
+        if (!adjust_eh_frame_pointer(&cursor, &length, LSDAencoding, eh_frame,
+                                     origAddr, elf))
+          goto malformed;
+      }
+    }
+
+    data += entryLength.value;
+    size -= entryLength.value;
+  }
+  return;
+
+malformed:
+  throw std::runtime_error("malformed .eh_frame");
+}
+
+template <typename Rel_Type>
+int do_relocation_section(Elf* elf, unsigned int rel_type,
+                          unsigned int rel_type2, bool force) {
+  ElfDynamic_Section* dyn = elf->getDynSection();
+  if (dyn == nullptr) {
+    fprintf(stderr, "Couldn't find SHT_DYNAMIC section\n");
+    return -1;
+  }
+
+  ElfRel_Section<Rel_Type>* section =
+      (ElfRel_Section<Rel_Type>*)dyn->getSectionForType(Rel_Type::d_tag);
+  if (section == nullptr) {
+    fprintf(stderr, "No relocations\n");
+    return -1;
+  }
+  assert(section->getType() == Rel_Type::sh_type);
+
+  Elf64_Shdr relhack64_section = {0,
+                                  SHT_PROGBITS,
+                                  SHF_ALLOC,
+                                  0,
+                                  (Elf64_Off)-1LL,
+                                  0,
+                                  SHN_UNDEF,
+                                  0,
+                                  Elf_Addr::size(elf->getClass()),
+                                  Elf_Addr::size(elf->getClass())};
+  Elf64_Shdr relhackcode64_section = {0,
+                                      SHT_PROGBITS,
+                                      SHF_ALLOC | SHF_EXECINSTR,
+                                      0,
+                                      (Elf64_Off)-1LL,
+                                      0,
+                                      SHN_UNDEF,
+                                      0,
+                                      1,
+                                      0};
+
+  unsigned int entry_sz = Elf_Addr::size(elf->getClass());
+
+  // The injected code needs to be executed before any init code in the
+  // binary. There are three possible cases:
+  // - The binary has no init code at all. In this case, we will add a
+  //   DT_INIT entry pointing to the injected code.
+  // - The binary has a DT_INIT entry. In this case, we will interpose:
+  //   we change DT_INIT to point to the injected code, and have the
+  //   injected code call the original DT_INIT entry point.
+  // - The binary has no DT_INIT entry, but has a DT_INIT_ARRAY. In this
+  //   case, we interpose as well, by replacing the first entry in the
+  //   array to point to the injected code, and have the injected code
+  //   call the original first entry.
+  // The binary may have .ctors instead of DT_INIT_ARRAY, for its init
+  // functions, but this falls into the second case above, since .ctors
+  // are actually run by DT_INIT code.
+  ElfValue* value = dyn->getValueForType(DT_INIT);
+  unsigned int original_init = value ? value->getValue() : 0;
+  ElfSection* init_array = nullptr;
+  if (!value || !value->getValue()) {
+    value = dyn->getValueForType(DT_INIT_ARRAYSZ);
+    if (value && value->getValue() >= entry_sz)
+      init_array = dyn->getSectionForType(DT_INIT_ARRAY);
+  }
+
+  Elf_Shdr relhack_section(relhack64_section);
+  Elf_Shdr relhackcode_section(relhackcode64_section);
+  auto relhack_ptr = std::make_unique<ElfRelHack_Section>(relhack_section);
+  auto relhack = relhack_ptr.get();
+
+  ElfSymtab_Section* symtab = (ElfSymtab_Section*)section->getLink();
+  Elf_SymValue* sym = symtab->lookup("__cxa_pure_virtual");
+
+  std::vector<Rel_Type> new_rels;
+  std::vector<Rel_Type> init_array_relocs;
+  size_t init_array_insert = 0;
+  for (typename std::vector<Rel_Type>::iterator i = section->rels.begin();
+       i != section->rels.end(); ++i) {
+    // We don't need to keep R_*_NONE relocations
+    if (!ELF64_R_TYPE(i->r_info)) continue;
+    ElfLocation loc(i->r_offset, elf);
+    // __cxa_pure_virtual is a function used in vtables to point at pure
+    // virtual methods. The __cxa_pure_virtual function usually abort()s.
+    // These functions are however normally never called. In the case
+    // where they would, jumping to the null address instead of calling
+    // __cxa_pure_virtual is going to work just as well. So we can remove
+    // relocations for the __cxa_pure_virtual symbol and null out the
+    // content at the offset pointed by the relocation.
+    if (sym) {
+      if (sym->defined) {
+        // If we are statically linked to libstdc++, the
+        // __cxa_pure_virtual symbol is defined in our lib, and we
+        // have relative relocations (rel_type) for it.
+        if (ELF64_R_TYPE(i->r_info) == rel_type) {
+          Elf_Addr addr(loc.getBuffer(), entry_sz, elf->getClass(),
+                        elf->getData());
+          if (addr.value == sym->value.getValue()) {
+            memset((char*)loc.getBuffer(), 0, entry_sz);
+            continue;
+          }
+        }
+      } else {
+        // If we are dynamically linked to libstdc++, the
+        // __cxa_pure_virtual symbol is undefined in our lib, and we
+        // have absolute relocations (rel_type2) for it.
+        if ((ELF64_R_TYPE(i->r_info) == rel_type2) &&
+            (sym == &symtab->syms[ELF64_R_SYM(i->r_info)])) {
+          memset((char*)loc.getBuffer(), 0, entry_sz);
+          continue;
+        }
+      }
+    }
+    // Keep track of the relocations associated with the init_array section.
+    if (init_array && i->r_offset >= init_array->getAddr() &&
+        i->r_offset < init_array->getAddr() + init_array->getSize()) {
+      init_array_relocs.push_back(*i);
+      init_array_insert = new_rels.size();
+    } else if (!(loc.getSection()->getFlags() & SHF_WRITE) ||
+               (ELF64_R_TYPE(i->r_info) != rel_type)) {
+      // Don't pack relocations happening in non writable sections.
+      // Our injected code is likely not to be allowed to write there.
+      new_rels.push_back(*i);
+    } else if (i->r_offset & 1) {
+      // RELR packing doesn't support relocations at an odd address, but
+      // there shouldn't be any.
+      new_rels.push_back(*i);
+    } else {
+      // With Elf_Rel, the value pointed by the relocation offset is the addend.
+      // With Elf_Rela, the addend is in the relocation entry, but the elfhacked
+      // relocation info doesn't contain it. Elfhack relies on the value pointed
+      // by the relocation offset to also contain the addend. Which is true with
+      // BFD ld and gold, but not lld, which leaves that nulled out. So if that
+      // value is nulled out, we update it to the addend.
+      Elf_Addr addr(loc.getBuffer(), entry_sz, elf->getClass(), elf->getData());
+      unsigned int addend = get_addend(&*i, elf);
+      if (addr.value == 0) {
+        addr.value = addend;
+        addr.serialize(const_cast<char*>(loc.getBuffer()), entry_sz,
+                       elf->getClass(), elf->getData());
+      } else if (addr.value != addend) {
+        fprintf(stderr,
+                "Relocation addend inconsistent with content. Skipping\n");
+        return -1;
+      }
+      relhack->push_back(i->r_offset);
+    }
+  }
+  // Last entry must be a nullptr
+  relhack->push_back(0);
+
+  if (init_array) {
+    // Some linkers create a DT_INIT_ARRAY section that, for all purposes,
+    // is empty: it only contains 0x0 or 0xffffffff pointers with no
+    // relocations. In some other cases, there can be null pointers with no
+    // relocations in the middle of the section. Example: crtend_so.o in the
+    // Android NDK contains a sized .init_array with a null pointer and no
+    // relocation, which ends up in all Android libraries, and in some cases it
+    // ends up in the middle of the final .init_array section. If we have such a
+    // reusable slot at the beginning of .init_array, we just use it. It we have
+    // one in the middle of .init_array, we slide its content to move the "hole"
+    // at the beginning and use it there (we need our injected code to run
+    // before any other). Otherwise, replace the first entry and keep the
+    // original pointer.
+    std::sort(init_array_relocs.begin(), init_array_relocs.end(),
+              [](Rel_Type& a, Rel_Type& b) { return a.r_offset < b.r_offset; });
+    size_t expected = init_array->getAddr();
+    const size_t zero = 0;
+    const size_t all = SIZE_MAX;
+    const char* data = init_array->getData();
+    size_t length = Elf_Addr::size(elf->getClass());
+    size_t off = 0;
+    for (; off < init_array_relocs.size(); off++) {
+      auto& r = init_array_relocs[off];
+      if (r.r_offset >= expected + length &&
+          (memcmp(data + off * length, &zero, length) == 0 ||
+           memcmp(data + off * length, &all, length) == 0)) {
+        // We found a hole, move the preceding entries.
+        while (off) {
+          auto& p = init_array_relocs[--off];
+          if (ELF64_R_TYPE(p.r_info) == rel_type) {
+            unsigned int addend = get_addend(&p, elf);
+            p.r_offset += length;
+            set_relative_reloc(&p, elf, addend);
+          } else {
+            fprintf(stderr,
+                    "Unsupported relocation type in DT_INIT_ARRAY. Skipping\n");
+            return -1;
+          }
+        }
+        break;
+      }
+      expected = r.r_offset + length;
+    }
+
+    if (off == 0) {
+      // We either found a hole above, and can now use the first entry,
+      // or the init_array section is effectively empty (see further above)
+      // and we also can use the first entry.
+      // Either way, code further below will take care of actually setting
+      // the right r_info and r_added for the relocation.
+      Rel_Type rel;
+      rel.r_offset = init_array->getAddr();
+      init_array_relocs.insert(init_array_relocs.begin(), rel);
+    } else {
+      // Use relocated value of DT_INIT_ARRAY's first entry for the
+      // function to be called by the injected code.
+      auto& rel = init_array_relocs[0];
+      unsigned int addend = get_addend(&rel, elf);
+      if (ELF64_R_TYPE(rel.r_info) == rel_type) {
+        original_init = addend;
+      } else if (ELF64_R_TYPE(rel.r_info) == rel_type2) {
+        ElfSymtab_Section* symtab = (ElfSymtab_Section*)section->getLink();
+        original_init =
+            symtab->syms[ELF64_R_SYM(rel.r_info)].value.getValue() + addend;
+      } else {
+        fprintf(stderr,
+                "Unsupported relocation type for DT_INIT_ARRAY's first entry. "
+                "Skipping\n");
+        return -1;
+      }
+    }
+
+    new_rels.insert(std::next(new_rels.begin(), init_array_insert),
+                    init_array_relocs.begin(), init_array_relocs.end());
+  }
+
+  unsigned int mprotect_cb = 0;
+  unsigned int sysconf_cb = 0;
+  // If there is a relro segment, our injected code will run after the linker
+  // sets the corresponding pages read-only. We need to make our code change
+  // that to read-write before applying relocations, which means it needs to
+  // call mprotect. To do that, we need to find a reference to the mprotect
+  // symbol. In case the library already has one, we use that, but otherwise, we
+  // add the symbol. Then the injected code needs to be able to call the
+  // corresponding function, which means it needs access to a pointer to it. We
+  // get such a pointer by making the linker apply a relocation for the symbol
+  // at an address our code can read. The problem here is that there is not much
+  // relocated space where we can put such a pointer, so we abuse the bss
+  // section temporarily (it will be restored to a null value before any code
+  // can actually use it)
+  if (elf->getSegmentByType(PT_GNU_RELRO)) {
+    ElfSection* gnu_versym = dyn->getSectionForType(DT_VERSYM);
+    auto lookup = [&symtab, &gnu_versym](const char* symbol) {
+      Elf_SymValue* sym_value = symtab->lookup(symbol, STT(FUNC));
+      if (!sym_value) {
+        symtab->syms.emplace_back();
+        sym_value = &symtab->syms.back();
+        symtab->grow(symtab->syms.size() * symtab->getEntSize());
+        sym_value->name =
+            ((ElfStrtab_Section*)symtab->getLink())->getStr(symbol);
+        sym_value->info = ELF64_ST_INFO(STB_GLOBAL, STT_FUNC);
+        sym_value->other = STV_DEFAULT;
+        new (&sym_value->value) ElfLocation(nullptr, 0, ElfLocation::ABSOLUTE);
+        sym_value->size = 0;
+        sym_value->defined = false;
+
+        // The DT_VERSYM data (in the .gnu.version section) has the same number
+        // of entries as the symbols table. Since we added one entry there, we
+        // need to add one entry here. Zeroes in the extra data means no version
+        // for that symbol, which is the simplest thing to do.
+        if (gnu_versym) {
+          gnu_versym->grow(gnu_versym->getSize() + gnu_versym->getEntSize());
+        }
+      }
+      return sym_value;
+    };
+
+    Elf_SymValue* mprotect = lookup("mprotect");
+    Elf_SymValue* sysconf = lookup("sysconf");
+
+    // Add relocations for the mprotect and sysconf symbols.
+    auto add_relocation_to = [&new_rels, &symtab, rel_type2](
+                                 Elf_SymValue* symbol, unsigned int location) {
+      new_rels.emplace_back();
+      Rel_Type& rel = new_rels.back();
+      memset(&rel, 0, sizeof(rel));
+      rel.r_info = ELF64_R_INFO(
+          std::distance(symtab->syms.begin(),
+                        std::vector<Elf_SymValue>::iterator(symbol)),
+          rel_type2);
+      rel.r_offset = location;
+      return location;
+    };
+
+    // Find the beginning of the bss section, and use an aligned location in
+    // there for the relocation.
+    for (ElfSection* s = elf->getSection(1); s != nullptr; s = s->getNext()) {
+      if (s->getType() != SHT_NOBITS ||
+          (s->getFlags() & (SHF_TLS | SHF_WRITE)) != SHF_WRITE) {
+        continue;
+      }
+      size_t ptr_size = Elf_Addr::size(elf->getClass());
+      size_t usable_start = (s->getAddr() + ptr_size - 1) & ~(ptr_size - 1);
+      size_t usable_end = (s->getAddr() + s->getSize()) & ~(ptr_size - 1);
+      if (usable_end - usable_start >= 2 * ptr_size) {
+        mprotect_cb = add_relocation_to(mprotect, usable_start);
+        sysconf_cb = add_relocation_to(sysconf, usable_start + ptr_size);
+        break;
+      }
+    }
+
+    if (mprotect_cb == 0 || sysconf_cb == 0) {
+      fprintf(stderr, "Couldn't find .bss. Skipping\n");
+      return -1;
+    }
+  }
+
+  size_t old_size = section->getSize();
+
+  section->rels.assign(new_rels.begin(), new_rels.end());
+  section->shrink(new_rels.size() * section->getEntSize());
+
+  auto relhackcode_ptr = std::make_unique<ElfRelHackCode_Section>(
+      relhackcode_section, *elf, *relhack, original_init, mprotect_cb,
+      sysconf_cb);
+  auto relhackcode = relhackcode_ptr.get();
+  // Find the first executable section, and insert the relhack code before
+  // that. The relhack data is inserted between .rel.dyn and .rel.plt.
+  ElfSection* first_executable = nullptr;
+  for (ElfSection* s = elf->getSection(1); s != nullptr; s = s->getNext()) {
+    if (s->getFlags() & SHF_EXECINSTR) {
+      first_executable = s;
+      break;
+    }
+  }
+
+  if (!first_executable) {
+    fprintf(stderr, "Couldn't find executable section. Skipping\n");
+    return -1;
+  }
+
+  // Once the pointers for relhack, relhackcode, and init are inserted,
+  // their ownership is transferred to the Elf object, which will free
+  // them when itself is freed. Hence the .release() calls here (and
+  // the init.release() call later on). Please note that the raw
+  // pointers will continue to be used after .release(), which is why
+  // we are caching them (since .release() will end up setting the
+  // smart pointer's internal raw pointer to nullptr).
+
+  relhack->insertBefore(section);
+  relhack_ptr.release();
+
+  relhackcode->insertBefore(first_executable);
+  relhackcode_ptr.release();
+
+  // Don't try further if we can't gain from the relocation section size change.
+  // We account for the fact we're going to split the PT_LOAD before the
+  // injected code section, so the overhead of the page alignment for section
+  // needs to be accounted for.
+  size_t align = first_executable->getSegmentByType(PT_LOAD)->getAlign();
+  size_t new_size = relhack->getSize() + section->getSize() +
+                    relhackcode->getSize() +
+                    (relhackcode->getAddr() & (align - 1));
+  if (!force && (new_size >= old_size || old_size - new_size < align)) {
+    fprintf(stderr, "No gain. Skipping\n");
+    return -1;
+  }
+
+  // .eh_frame/.eh_frame_hdr may be between the relocation sections and the
+  // executable sections. When that happens, we may end up creating a separate
+  // PT_LOAD for just both of them because they are not considered relocatable.
+  // But they are, in fact, kind of relocatable, albeit with some manual work.
+  // Which we'll do here.
+  ElfSegment* eh_frame_segment = elf->getSegmentByType(PT_GNU_EH_FRAME);
+  ElfSection* eh_frame_hdr =
+      eh_frame_segment ? eh_frame_segment->getFirstSection() : nullptr;
+  // The .eh_frame section usually follows the eh_frame_hdr section.
+  ElfSection* eh_frame = eh_frame_hdr ? eh_frame_hdr->getNext() : nullptr;
+  ElfSection* first = eh_frame_hdr;
+  ElfSection* second = eh_frame;
+  if (eh_frame && strcmp(eh_frame->getName(), ".eh_frame")) {
+    // But sometimes it appears *before* the eh_frame_hdr section.
+    eh_frame = eh_frame_hdr->getPrevious();
+    first = eh_frame;
+    second = eh_frame_hdr;
+  }
+  if (eh_frame_hdr && (!eh_frame || strcmp(eh_frame->getName(), ".eh_frame"))) {
+    throw std::runtime_error(
+        "Expected to find an .eh_frame section adjacent to .eh_frame_hdr");
+  }
+  if (eh_frame && first->getAddr() > relhack->getAddr() &&
+      second->getAddr() < first_executable->getAddr()) {
+    // The distance between both sections needs to be preserved because
+    // eh_frame_hdr contains relative offsets to eh_frame. Well, they could be
+    // relocated too, but it's not worth the effort for the few number of bytes
+    // this would save.
+    unsigned int distance = second->getAddr() - first->getAddr();
+    unsigned int origAddr = eh_frame->getAddr();
+    ElfSection* previous = first->getPrevious();
+    first->getShdr().sh_addr = (previous->getAddr() + previous->getSize() +
+                                first->getAddrAlign() - 1) &
+                               ~(first->getAddrAlign() - 1);
+    second->getShdr().sh_addr =
+        (first->getAddr() + std::min(first->getSize(), distance) +
+         second->getAddrAlign() - 1) &
+        ~(second->getAddrAlign() - 1);
+    // Re-adjust to keep the original distance.
+    // If the first section has a smaller alignment requirement than the second,
+    // the second will be farther away, so we need to adjust the first.
+    // If the second section has a smaller alignment requirement than the first,
+    // it will already be at the right distance.
+    first->getShdr().sh_addr = second->getAddr() - distance;
+    assert(distance == second->getAddr() - first->getAddr());
+    first->markDirty();
+    adjust_eh_frame(eh_frame, origAddr, elf);
+  }
+
+  // Adjust PT_LOAD segments
+  for (ElfSegment* segment = elf->getSegmentByType(PT_LOAD); segment;
+       segment = elf->getSegmentByType(PT_LOAD, segment)) {
+    maybe_split_segment(elf, segment);
+  }
+
+  // Ensure Elf sections will be at their final location.
+  elf->normalize();
+  auto init =
+      std::make_unique<ElfLocation>(relhackcode, relhackcode->getEntryPoint());
+  if (init_array) {
+    // Adjust the first DT_INIT_ARRAY entry to point at the injected code
+    // by transforming its relocation into a relative one pointing to the
+    // address of the injected code.
+    Rel_Type* rel = &section->rels[init_array_insert];
+    rel->r_info = ELF64_R_INFO(0, rel_type);  // Set as a relative relocation
+    set_relative_reloc(rel, elf, init->getValue());
+  } else {
+    if (dyn->setValueForType(DT_INIT, init.get())) {
+      init.release();
+    } else {
+      fprintf(stderr, "Can't grow .dynamic section to set DT_INIT. Skipping\n");
+      return -1;
+    }
+  }
+
+  // TODO: adjust the value according to the remaining number of relative
+  // relocations
+  if (dyn->getValueForType(Rel_Type::d_tag_count))
+    dyn->setValueForType(Rel_Type::d_tag_count, new ElfPlainValue(0));
+
+  return 0;
+}
+
+static inline int backup_file(const char* name) {
+  std::string fname(name);
+  fname += ".bak";
+  return rename(name, fname.c_str());
+}
+
+void do_file(const char* name, bool backup = false, bool force = false) {
+  std::ifstream file(name, std::ios::in | std::ios::binary);
+  Elf elf(file);
+  unsigned int size = elf.getSize();
+  fprintf(stderr, "%s: ", name);
+  if (elf.getType() != ET_DYN) {
+    fprintf(stderr, "Not a shared object. Skipping\n");
+    return;
+  }
+
+  for (ElfSection* section = elf.getSection(1); section != nullptr;
+       section = section->getNext()) {
+    if (section->getName() &&
+        (strncmp(section->getName(), ".elfhack.", 9) == 0)) {
+      fprintf(stderr, "Already elfhacked. Skipping\n");
+      return;
+    }
+  }
+
+  int exit = -1;
+  switch (elf.getMachine()) {
+    case EM_386:
+      exit =
+          do_relocation_section<Elf_Rel>(&elf, R_386_RELATIVE, R_386_32, force);
+      break;
+    case EM_X86_64:
+      exit = do_relocation_section<Elf_Rela>(&elf, R_X86_64_RELATIVE,
+                                             R_X86_64_64, force);
+      break;
+    case EM_ARM:
+      exit = do_relocation_section<Elf_Rel>(&elf, R_ARM_RELATIVE, R_ARM_ABS32,
+                                            force);
+      break;
+    case EM_AARCH64:
+      exit = do_relocation_section<Elf_Rela>(&elf, R_AARCH64_RELATIVE,
+                                             R_AARCH64_ABS64, force);
+      break;
+    default:
+      throw std::runtime_error("unsupported architecture");
+  }
+  if (exit == 0) {
+    if (!force && (elf.getSize() >= size)) {
+      fprintf(stderr, "No gain. Skipping\n");
+    } else if (backup && backup_file(name) != 0) {
+      fprintf(stderr, "Couln't create backup file\n");
+    } else {
+      std::ofstream ofile(name,
+                          std::ios::out | std::ios::binary | std::ios::trunc);
+      elf.write(ofile);
+      fprintf(stderr, "Reduced by %d bytes\n", size - elf.getSize());
+    }
+  }
+}
+
+void undo_file(const char* name, bool backup = false) {
+  std::ifstream file(name, std::ios::in | std::ios::binary);
+  Elf elf(file);
+  unsigned int size = elf.getSize();
+  fprintf(stderr, "%s: ", name);
+  if (elf.getType() != ET_DYN) {
+    fprintf(stderr, "Not a shared object. Skipping\n");
+    return;
+  }
+
+  ElfSection *data = nullptr, *text = nullptr;
+  for (ElfSection* section = elf.getSection(1); section != nullptr;
+       section = section->getNext()) {
+    if (section->getName() && (strcmp(section->getName(), elfhack_data) == 0))
+      data = section;
+    if (section->getName() && (strcmp(section->getName(), elfhack_text) == 0))
+      text = section;
+  }
+
+  if (!data || !text) {
+    fprintf(stderr, "Not elfhacked. Skipping\n");
+    return;
+  }
+
+  // When both elfhack sections are in the same segment, try to merge
+  // the segment that contains them both and the following segment.
+  // When the elfhack sections are in separate segments, try to merge
+  // those segments.
+  ElfSegment* first = data->getSegmentByType(PT_LOAD);
+  ElfSegment* second = text->getSegmentByType(PT_LOAD);
+  if (first == second) {
+    second = elf.getSegmentByType(PT_LOAD, first);
+  }
+
+  // Only merge the segments when their flags match.
+  if (second->getFlags() != first->getFlags()) {
+    fprintf(stderr, "Couldn't merge PT_LOAD segments. Skipping\n");
+    return;
+  }
+  // Move sections from the second PT_LOAD to the first, and remove the
+  // second PT_LOAD segment.
+  for (std::list<ElfSection*>::iterator section = second->begin();
+       section != second->end(); ++section)
+    first->addSection(*section);
+
+  elf.removeSegment(second);
+  elf.normalize();
+
+  if (backup && backup_file(name) != 0) {
+    fprintf(stderr, "Couln't create backup file\n");
+  } else {
+    std::ofstream ofile(name,
+                        std::ios::out | std::ios::binary | std::ios::trunc);
+    elf.write(ofile);
+    fprintf(stderr, "Grown by %d bytes\n", elf.getSize() - size);
+  }
+}
+
+int main(int argc, char* argv[]) {
+  int arg;
+  bool backup = false;
+  bool force = false;
+  bool revert = false;
+  char* lastSlash = rindex(argv[0], '/');
+  if (lastSlash != nullptr) rundir = strndup(argv[0], lastSlash - argv[0]);
+  for (arg = 1; arg < argc; arg++) {
+    if (strcmp(argv[arg], "-f") == 0)
+      force = true;
+    else if (strcmp(argv[arg], "-b") == 0)
+      backup = true;
+    else if (strcmp(argv[arg], "-r") == 0)
+      revert = true;
+    else if (revert) {
+      undo_file(argv[arg], backup);
+    } else
+      do_file(argv[arg], backup, force);
+  }
+
+  free(rundir);
+  return 0;
+}
diff --git a/build/unix/elfhack/elfxx.h b/build/unix/elfhack/elfxx.h
new file mode 100644
index 0000000000..15488a78f8
--- /dev/null
+++ b/build/unix/elfhack/elfxx.h
@@ -0,0 +1,701 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <stdexcept>
+#include <list>
+#include <vector>
+#include <cstring>
+#include <iostream>
+#include <fstream>
+#include <algorithm>
+#include <elf.h>
+#include <asm/byteorder.h>
+
+// Technically, __*_to_cpu and __cpu_to* function are equivalent,
+// so swap can use either of both.
+#define def_swap(endian, type, bits)                    \
+  static inline type##bits##_t swap(type##bits##_t i) { \
+    return __##endian##bits##_to_cpu(i);                \
+  }
+
+class little_endian {
+ public:
+  def_swap(le, uint, 16);
+  def_swap(le, uint, 32);
+  def_swap(le, uint, 64);
+  def_swap(le, int, 16);
+  def_swap(le, int, 32);
+  def_swap(le, int, 64);
+};
+
+class big_endian {
+ public:
+  def_swap(be, uint, 16);
+  def_swap(be, uint, 32);
+  def_swap(be, uint, 64);
+  def_swap(be, int, 16);
+  def_swap(be, int, 32);
+  def_swap(be, int, 64);
+};
+
+// forward declaration
+class ElfSection;
+class ElfSegment;
+// TODO: Rename Elf_* types
+class Elf_Ehdr;
+class Elf_Phdr;
+class Elf;
+class ElfDynamic_Section;
+class ElfStrtab_Section;
+
+template <typename X>
+class FixedSizeData {
+ public:
+  struct Wrapper {
+    X value;
+  };
+  typedef Wrapper Type32;
+  typedef Wrapper Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r) {
+    r.value = endian::swap(t.value);
+  }
+};
+
+class Elf_Ehdr_Traits {
+ public:
+  typedef Elf32_Ehdr Type32;
+  typedef Elf64_Ehdr Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r);
+};
+
+class Elf_Phdr_Traits {
+ public:
+  typedef Elf32_Phdr Type32;
+  typedef Elf64_Phdr Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r);
+};
+
+class Elf_Shdr_Traits {
+ public:
+  typedef Elf32_Shdr Type32;
+  typedef Elf64_Shdr Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r);
+};
+
+class Elf_Dyn_Traits {
+ public:
+  typedef Elf32_Dyn Type32;
+  typedef Elf64_Dyn Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r);
+};
+
+class Elf_Sym_Traits {
+ public:
+  typedef Elf32_Sym Type32;
+  typedef Elf64_Sym Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r);
+};
+
+class Elf_Rel_Traits {
+ public:
+  typedef Elf32_Rel Type32;
+  typedef Elf64_Rel Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r);
+};
+
+class Elf_Rela_Traits {
+ public:
+  typedef Elf32_Rela Type32;
+  typedef Elf64_Rela Type64;
+
+  template <class endian, typename R, typename T>
+  static void swap(T& t, R& r);
+};
+
+class ElfValue {
+ public:
+  virtual unsigned int getValue() { return 0; }
+  virtual ElfSection* getSection() { return nullptr; }
+};
+
+class ElfPlainValue : public ElfValue {
+  unsigned int value;
+
+ public:
+  ElfPlainValue(unsigned int val) : value(val){};
+  unsigned int getValue() { return value; }
+};
+
+class ElfLocation : public ElfValue {
+  ElfSection* section;
+  unsigned int offset;
+
+ public:
+  enum position { ABSOLUTE, RELATIVE };
+  ElfLocation() : section(nullptr), offset(0){};
+  ElfLocation(ElfSection* section, unsigned int off,
+              enum position pos = RELATIVE);
+  ElfLocation(unsigned int location, Elf* elf);
+  unsigned int getValue();
+  ElfSection* getSection() { return section; }
+  const char* getBuffer();
+};
+
+class ElfSize : public ElfValue {
+  ElfSection* section;
+
+ public:
+  ElfSize(ElfSection* s) : section(s){};
+  unsigned int getValue();
+  ElfSection* getSection() { return section; }
+};
+
+class ElfEntSize : public ElfValue {
+  ElfSection* section;
+
+ public:
+  ElfEntSize(ElfSection* s) : section(s){};
+  unsigned int getValue();
+  ElfSection* getSection() { return section; }
+};
+
+template <typename T>
+class serializable : public T::Type64 {
+ public:
+  serializable(){};
+  serializable(const typename T::Type64& p) : T::Type64(p){};
+
+ private:
+  template <typename R>
+  void init(const char* buf, size_t len, unsigned char ei_data) {
+    R e;
+    assert(len >= sizeof(e));
+    memcpy(&e, buf, sizeof(e));
+    if (ei_data == ELFDATA2LSB) {
+      T::template swap<little_endian>(e, *this);
+      return;
+    } else if (ei_data == ELFDATA2MSB) {
+      T::template swap<big_endian>(e, *this);
+      return;
+    }
+    throw std::runtime_error("Unsupported ELF data encoding");
+  }
+
+  template <typename R>
+  void serialize(const char* buf, size_t len, unsigned char ei_data) {
+    assert(len >= sizeof(R));
+    if (ei_data == ELFDATA2LSB) {
+      T::template swap<little_endian>(*this, *(R*)buf);
+      return;
+    } else if (ei_data == ELFDATA2MSB) {
+      T::template swap<big_endian>(*this, *(R*)buf);
+      return;
+    }
+    throw std::runtime_error("Unsupported ELF data encoding");
+  }
+
+ public:
+  serializable(const char* buf, size_t len, unsigned char ei_class,
+               unsigned char ei_data) {
+    if (ei_class == ELFCLASS32) {
+      init<typename T::Type32>(buf, len, ei_data);
+      return;
+    } else if (ei_class == ELFCLASS64) {
+      init<typename T::Type64>(buf, len, ei_data);
+      return;
+    }
+    throw std::runtime_error("Unsupported ELF class");
+  }
+
+  serializable(std::ifstream& file, unsigned char ei_class,
+               unsigned char ei_data) {
+    if (ei_class == ELFCLASS32) {
+      typename T::Type32 e;
+      file.read((char*)&e, sizeof(e));
+      init<typename T::Type32>((char*)&e, sizeof(e), ei_data);
+      return;
+    } else if (ei_class == ELFCLASS64) {
+      typename T::Type64 e;
+      file.read((char*)&e, sizeof(e));
+      init<typename T::Type64>((char*)&e, sizeof(e), ei_data);
+      return;
+    }
+    throw std::runtime_error("Unsupported ELF class or data encoding");
+  }
+
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data) {
+    if (ei_class == ELFCLASS32) {
+      typename T::Type32 e;
+      serialize<typename T::Type32>((char*)&e, sizeof(e), ei_data);
+      file.write((char*)&e, sizeof(e));
+      return;
+    } else if (ei_class == ELFCLASS64) {
+      typename T::Type64 e;
+      serialize<typename T::Type64>((char*)&e, sizeof(e), ei_data);
+      file.write((char*)&e, sizeof(e));
+      return;
+    }
+    throw std::runtime_error("Unsupported ELF class or data encoding");
+  }
+
+  void serialize(char* buf, size_t len, unsigned char ei_class,
+                 unsigned char ei_data) {
+    if (ei_class == ELFCLASS32) {
+      serialize<typename T::Type32>(buf, len, ei_data);
+      return;
+    } else if (ei_class == ELFCLASS64) {
+      serialize<typename T::Type64>(buf, len, ei_data);
+      return;
+    }
+    throw std::runtime_error("Unsupported ELF class");
+  }
+
+  static inline unsigned int size(unsigned char ei_class) {
+    if (ei_class == ELFCLASS32)
+      return sizeof(typename T::Type32);
+    else if (ei_class == ELFCLASS64)
+      return sizeof(typename T::Type64);
+    return 0;
+  }
+};
+
+typedef serializable<Elf_Shdr_Traits> Elf_Shdr;
+
+class Elf {
+ public:
+  Elf(std::ifstream& file);
+  ~Elf();
+
+  /* index == -1 is treated as index == ehdr.e_shstrndx */
+  ElfSection* getSection(int index);
+
+  ElfSection* getSectionAt(unsigned int offset);
+
+  ElfSegment* getSegmentByType(unsigned int type, ElfSegment* last = nullptr);
+
+  ElfDynamic_Section* getDynSection();
+
+  void normalize();
+  void write(std::ofstream& file);
+
+  unsigned char getClass();
+  unsigned char getData();
+  unsigned char getType();
+  unsigned char getMachine();
+  unsigned int getSize();
+
+  void insertSegmentAfter(ElfSegment* previous, ElfSegment* segment) {
+    std::vector<ElfSegment*>::iterator prev =
+        std::find(segments.begin(), segments.end(), previous);
+    segments.insert(prev + 1, segment);
+  }
+
+  void removeSegment(ElfSegment* segment);
+
+ private:
+  Elf_Ehdr* ehdr;
+  ElfLocation eh_entry;
+  ElfStrtab_Section* eh_shstrndx;
+  ElfSection** sections;
+  std::vector<ElfSegment*> segments;
+  ElfSection *shdr_section, *phdr_section;
+  /* Values used only during initialization */
+  Elf_Shdr** tmp_shdr;
+  std::ifstream* tmp_file;
+};
+
+class ElfSection {
+ public:
+  typedef union {
+    ElfSection* section;
+    int index;
+  } SectionInfo;
+
+  ElfSection(Elf_Shdr& s, std::ifstream* file, Elf* parent);
+
+  virtual ~ElfSection() { free(data); }
+
+  const char* getName() { return name; }
+  unsigned int getType() { return shdr.sh_type; }
+  unsigned int getFlags() { return shdr.sh_flags; }
+  unsigned int getAddr();
+  unsigned int getSize() { return shdr.sh_size; }
+  unsigned int getAddrAlign() { return shdr.sh_addralign; }
+  unsigned int getEntSize() { return shdr.sh_entsize; }
+  const char* getData() { return data; }
+  ElfSection* getLink() { return link; }
+  SectionInfo getInfo() { return info; }
+
+  void shrink(unsigned int newsize) {
+    if (newsize < shdr.sh_size) {
+      shdr.sh_size = newsize;
+      markDirty();
+    }
+  }
+
+  void grow(unsigned int newsize) {
+    if (newsize > shdr.sh_size) {
+      data = static_cast<char*>(realloc(data, newsize));
+      memset(data + shdr.sh_size, 0, newsize - shdr.sh_size);
+      shdr.sh_size = newsize;
+      markDirty();
+    }
+  }
+
+  unsigned int getOffset();
+  int getIndex();
+  Elf_Shdr& getShdr();
+
+  ElfSection* getNext() { return next; }
+  ElfSection* getPrevious() { return previous; }
+
+  virtual bool isRelocatable() {
+    return ((getType() == SHT_SYMTAB) || (getType() == SHT_STRTAB) ||
+            (getType() == SHT_RELA) || (getType() == SHT_HASH) ||
+            (getType() == SHT_NOTE) || (getType() == SHT_REL) ||
+            (getType() == SHT_DYNSYM) || (getType() == SHT_GNU_HASH) ||
+            (getType() == SHT_GNU_verdef) || (getType() == SHT_GNU_verneed) ||
+            (getType() == SHT_GNU_versym) || getSegmentByType(PT_INTERP)) &&
+           (getFlags() & SHF_ALLOC);
+  }
+
+  void insertAfter(ElfSection* section, bool dirty = true) {
+    if (previous != nullptr) previous->next = next;
+    if (next != nullptr) next->previous = previous;
+    previous = section;
+    if (section != nullptr) {
+      next = section->next;
+      section->next = this;
+    } else
+      next = nullptr;
+    if (next != nullptr) next->previous = this;
+    if (dirty) markDirty();
+    insertInSegments(section->segments);
+  }
+
+  virtual void insertBefore(ElfSection* section, bool dirty = true) {
+    if (previous != nullptr) previous->next = next;
+    if (next != nullptr) next->previous = previous;
+    next = section;
+    if (section != nullptr) {
+      previous = section->previous;
+      section->previous = this;
+    } else
+      previous = nullptr;
+    if (previous != nullptr) previous->next = this;
+    if (dirty) markDirty();
+    insertInSegments(section->segments);
+  }
+
+  void markDirty() {
+    if (link != nullptr) shdr.sh_link = -1;
+    if (info.index) shdr.sh_info = -1;
+    shdr.sh_offset = -1;
+    if (isRelocatable()) shdr.sh_addr = -1;
+    if (next) next->markDirty();
+  }
+
+  virtual void serialize(std::ofstream& file, unsigned char ei_class,
+                         unsigned char ei_data) {
+    if (getType() == SHT_NOBITS) return;
+    file.seekp(getOffset());
+    file.write(data, getSize());
+  }
+
+  ElfSegment* getSegmentByType(unsigned int type);
+
+ private:
+  friend class ElfSegment;
+
+  void addToSegment(ElfSegment* segment) { segments.push_back(segment); }
+
+  void removeFromSegment(ElfSegment* segment) {
+    std::vector<ElfSegment*>::iterator i =
+        std::find(segments.begin(), segments.end(), segment);
+    segments.erase(i, i + 1);
+  }
+
+  void insertInSegments(std::vector<ElfSegment*>& segs);
+
+ protected:
+  Elf_Shdr shdr;
+  char* data;
+  const char* name;
+
+ private:
+  ElfSection* link;
+  SectionInfo info;
+  ElfSection *next, *previous;
+  int index;
+  std::vector<ElfSegment*> segments;
+};
+
+class ElfSegment {
+ public:
+  ElfSegment(Elf_Phdr* phdr);
+
+  unsigned int getType() { return type; }
+  unsigned int getFlags() { return flags; }
+  unsigned int getAlign() { return align; }
+
+  ElfSection* getFirstSection() {
+    return sections.empty() ? nullptr : sections.front();
+  }
+  int getVPDiff() { return v_p_diff; }
+  unsigned int getFileSize();
+  unsigned int getMemSize();
+  unsigned int getOffset();
+  unsigned int getAddr();
+
+  void addSection(ElfSection* section);
+  void removeSection(ElfSection* section);
+
+  std::list<ElfSection*>::iterator begin() { return sections.begin(); }
+  std::list<ElfSection*>::iterator end() { return sections.end(); }
+
+  void clear();
+
+ private:
+  unsigned int type;
+  int v_p_diff;  // Difference between physical and virtual address
+  unsigned int flags;
+  unsigned int align;
+  std::list<ElfSection*> sections;
+  // The following are only really used for PT_GNU_RELRO until something
+  // better is found.
+  unsigned int vaddr;
+  unsigned int filesz, memsz;
+};
+
+class Elf_Ehdr : public serializable<Elf_Ehdr_Traits>, public ElfSection {
+ public:
+  Elf_Ehdr(std::ifstream& file, unsigned char ei_class, unsigned char ei_data);
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data) {
+    serializable<Elf_Ehdr_Traits>::serialize(file, ei_class, ei_data);
+  }
+};
+
+class Elf_Phdr : public serializable<Elf_Phdr_Traits> {
+ public:
+  Elf_Phdr(){};
+  Elf_Phdr(std::ifstream& file, unsigned char ei_class, unsigned char ei_data)
+      : serializable<Elf_Phdr_Traits>(file, ei_class, ei_data){};
+  bool contains(ElfSection* section) {
+    unsigned int size = section->getSize();
+    unsigned int addr = section->getAddr();
+    // This may be biased, but should work in most cases
+    if ((section->getFlags() & SHF_ALLOC) == 0) return false;
+    // Special case for PT_DYNAMIC. Eventually, this should
+    // be better handled than special cases
+    if ((p_type == PT_DYNAMIC) && (section->getType() != SHT_DYNAMIC))
+      return false;
+    // Special case for PT_TLS.
+    if ((p_type == PT_TLS) && !(section->getFlags() & SHF_TLS)) return false;
+    return (addr >= p_vaddr) && (addr + size <= p_vaddr + p_memsz);
+  }
+};
+
+typedef serializable<Elf_Dyn_Traits> Elf_Dyn;
+
+struct Elf_DynValue {
+  unsigned int tag;
+  ElfValue* value;
+};
+
+class ElfDynamic_Section : public ElfSection {
+ public:
+  ElfDynamic_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent);
+  ~ElfDynamic_Section();
+
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data);
+
+  ElfValue* getValueForType(unsigned int tag);
+  ElfSection* getSectionForType(unsigned int tag);
+  bool setValueForType(unsigned int tag, ElfValue* val);
+
+ private:
+  std::vector<Elf_DynValue> dyns;
+};
+
+typedef serializable<Elf_Sym_Traits> Elf_Sym;
+
+struct Elf_SymValue {
+  const char* name;
+  unsigned char info;
+  unsigned char other;
+  ElfLocation value;
+  unsigned int size;
+  bool defined;
+};
+
+#define STT(type) (1 << STT_##type)
+
+class ElfSymtab_Section : public ElfSection {
+ public:
+  ElfSymtab_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent);
+
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data);
+
+  Elf_SymValue* lookup(const char* name,
+                       unsigned int type_filter = STT(OBJECT) | STT(FUNC));
+
+  // private: // Until we have a real API
+  std::vector<Elf_SymValue> syms;
+};
+
+class Elf_Rel : public serializable<Elf_Rel_Traits> {
+ public:
+  Elf_Rel() : serializable<Elf_Rel_Traits>(){};
+
+  Elf_Rel(std::ifstream& file, unsigned char ei_class, unsigned char ei_data)
+      : serializable<Elf_Rel_Traits>(file, ei_class, ei_data){};
+
+  static const unsigned int sh_type = SHT_REL;
+  static const unsigned int d_tag = DT_REL;
+  static const unsigned int d_tag_count = DT_RELCOUNT;
+};
+
+class Elf_Rela : public serializable<Elf_Rela_Traits> {
+ public:
+  Elf_Rela() : serializable<Elf_Rela_Traits>(){};
+
+  Elf_Rela(std::ifstream& file, unsigned char ei_class, unsigned char ei_data)
+      : serializable<Elf_Rela_Traits>(file, ei_class, ei_data){};
+
+  static const unsigned int sh_type = SHT_RELA;
+  static const unsigned int d_tag = DT_RELA;
+  static const unsigned int d_tag_count = DT_RELACOUNT;
+};
+
+template <class Rel>
+class ElfRel_Section : public ElfSection {
+ public:
+  ElfRel_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent)
+      : ElfSection(s, file, parent) {
+    auto pos = file->tellg();
+    file->seekg(shdr.sh_offset);
+    for (unsigned int i = 0; i < s.sh_size / s.sh_entsize; i++) {
+      Rel r(*file, parent->getClass(), parent->getData());
+      rels.push_back(r);
+    }
+    file->seekg(pos);
+  }
+
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data) {
+    for (typename std::vector<Rel>::iterator i = rels.begin(); i != rels.end();
+         ++i)
+      (*i).serialize(file, ei_class, ei_data);
+  }
+  // private: // Until we have a real API
+  std::vector<Rel> rels;
+};
+
+class ElfStrtab_Section : public ElfSection {
+ public:
+  ElfStrtab_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent)
+      : ElfSection(s, file, parent) {
+    table.push_back(table_storage(data, shdr.sh_size));
+  }
+
+  ~ElfStrtab_Section() {
+    for (std::vector<table_storage>::iterator t = table.begin() + 1;
+         t != table.end(); ++t)
+      delete[] t->buf;
+  }
+
+  const char* getStr(unsigned int index);
+
+  const char* getStr(const char* string);
+
+  unsigned int getStrIndex(const char* string);
+
+  void serialize(std::ofstream& file, unsigned char ei_class,
+                 unsigned char ei_data);
+
+ private:
+  struct table_storage {
+    unsigned int size, used;
+    char* buf;
+
+    table_storage() : size(4096), used(0), buf(new char[4096]) {}
+    table_storage(const char* data, unsigned int sz)
+        : size(sz), used(sz), buf(const_cast<char*>(data)) {}
+  };
+  std::vector<table_storage> table;
+};
+
+inline unsigned char Elf::getClass() { return ehdr->e_ident[EI_CLASS]; }
+
+inline unsigned char Elf::getData() { return ehdr->e_ident[EI_DATA]; }
+
+inline unsigned char Elf::getType() { return ehdr->e_type; }
+
+inline unsigned char Elf::getMachine() { return ehdr->e_machine; }
+
+inline unsigned int Elf::getSize() {
+  ElfSection* section;
+  for (section = shdr_section /* It's usually not far from the end */;
+       section->getNext() != nullptr; section = section->getNext())
+    ;
+  return section->getOffset() + section->getSize();
+}
+
+inline ElfSegment* ElfSection::getSegmentByType(unsigned int type) {
+  for (std::vector<ElfSegment*>::iterator seg = segments.begin();
+       seg != segments.end(); ++seg)
+    if ((*seg)->getType() == type) return *seg;
+  return nullptr;
+}
+
+inline void ElfSection::insertInSegments(std::vector<ElfSegment*>& segs) {
+  for (std::vector<ElfSegment*>::iterator it = segs.begin(); it != segs.end();
+       ++it) {
+    (*it)->addSection(this);
+  }
+}
+
+inline ElfLocation::ElfLocation(ElfSection* section, unsigned int off,
+                                enum position pos)
+    : section(section) {
+  if ((pos == ABSOLUTE) && section)
+    offset = off - section->getAddr();
+  else
+    offset = off;
+}
+
+inline ElfLocation::ElfLocation(unsigned int location, Elf* elf) {
+  section = elf->getSectionAt(location);
+  offset = location - (section ? section->getAddr() : 0);
+}
+
+inline unsigned int ElfLocation::getValue() {
+  return (section ? section->getAddr() : 0) + offset;
+}
+
+inline const char* ElfLocation::getBuffer() {
+  return section ? section->getData() + offset : nullptr;
+}
+
+inline unsigned int ElfSize::getValue() { return section->getSize(); }
+
+inline unsigned int ElfEntSize::getValue() { return section->getEntSize(); }
diff --git a/build/unix/elfhack/inject.c b/build/unix/elfhack/inject.c
new file mode 100644
index 0000000000..9e8399a1d1
--- /dev/null
+++ b/build/unix/elfhack/inject.c
@@ -0,0 +1,136 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <elf.h>
+
+/* The Android NDK headers define those */
+#undef Elf_Ehdr
+#undef Elf_Addr
+
+#if defined(__LP64__)
+#  define Elf_Ehdr Elf64_Ehdr
+#  define Elf_Addr Elf64_Addr
+#else
+#  define Elf_Ehdr Elf32_Ehdr
+#  define Elf_Addr Elf32_Addr
+#endif
+
+// On ARM, PC-relative function calls have a limit in how far they can jump,
+// which might not be enough for e.g. libxul.so. The easy way out would be
+// to use the long_call attribute, which forces the compiler to generate code
+// that can call anywhere, but clang doesn't support the attribute yet
+// (https://bugs.llvm.org/show_bug.cgi?id=40623), and while the command-line
+// equivalent does exist, it's currently broken
+// (https://bugs.llvm.org/show_bug.cgi?id=40624). So we create a manual
+// trampoline, corresponding to the code GCC generates with long_call.
+#ifdef __arm__
+__attribute__((section(".text._init_trampoline"), naked)) int init_trampoline(
+    int argc, char** argv, char** env) {
+  __asm__ __volatile__(
+      // thumb doesn't allow to use r12/ip with ldr, and thus would require an
+      // additional push/pop to save/restore the modified register, which would
+      // also change the call into a blx. It's simpler to switch to arm.
+      ".arm\n"
+      "  ldr ip, .LADDR\n"
+      ".LAFTER:\n"
+      "  add ip, pc, ip\n"
+      "  bx ip\n"
+      ".LADDR:\n"
+      "  .word real_original_init-(.LAFTER+8)\n");
+}
+#endif
+
+extern __attribute__((visibility("hidden"))) void original_init(int argc,
+                                                                char** argv,
+                                                                char** env);
+
+extern __attribute__((visibility("hidden"))) Elf_Addr relhack[];
+extern __attribute__((visibility("hidden"))) Elf_Ehdr elf_header;
+
+extern __attribute__((visibility("hidden"))) int (*mprotect_cb)(void* addr,
+                                                                size_t len,
+                                                                int prot);
+extern __attribute__((visibility("hidden"))) long (*sysconf_cb)(int name);
+extern __attribute__((visibility("hidden"))) char relro_start[];
+extern __attribute__((visibility("hidden"))) char relro_end[];
+
+static inline __attribute__((always_inline)) void do_relocations(void) {
+  Elf_Addr* ptr;
+  for (Elf_Addr* entry = relhack; *entry; entry++) {
+    if ((*entry & 1) == 0) {
+      ptr = (Elf_Addr*)((intptr_t)&elf_header + *entry);
+      *ptr += (intptr_t)&elf_header;
+    } else {
+      size_t remaining = (8 * sizeof(Elf_Addr) - 1);
+      Elf_Addr bits = *entry;
+      do {
+        bits >>= 1;
+        remaining--;
+        ptr++;
+        if (bits & 1) {
+          *ptr += (intptr_t)&elf_header;
+        }
+      } while (bits);
+      ptr += remaining;
+    }
+  }
+}
+
+__attribute__((section(".text._init_noinit"))) int init_noinit(int argc,
+                                                               char** argv,
+                                                               char** env) {
+  do_relocations();
+  return 0;
+}
+
+__attribute__((section(".text._init"))) int init(int argc, char** argv,
+                                                 char** env) {
+  do_relocations();
+  original_init(argc, argv, env);
+  // Ensure there is no tail-call optimization, avoiding the use of the
+  // B.W instruction in Thumb for the call above.
+  return 0;
+}
+
+static inline __attribute__((always_inline)) void do_relocations_with_relro(
+    void) {
+  long page_size = sysconf_cb(_SC_PAGESIZE);
+  uintptr_t aligned_relro_start = ((uintptr_t)relro_start) & ~(page_size - 1);
+  // The relro segment may not end at a page boundary. If that's the case, the
+  // remainder of the page needs to stay read-write, so the last page is never
+  // set read-only. Thus the aligned relro end is page-rounded down.
+  uintptr_t aligned_relro_end = ((uintptr_t)relro_end) & ~(page_size - 1);
+  // By the time the injected code runs, the relro segment is read-only. But
+  // we want to apply relocations in it, so we set it r/w first. We'll restore
+  // it to read-only in relro_post.
+  mprotect_cb((void*)aligned_relro_start,
+              aligned_relro_end - aligned_relro_start, PROT_READ | PROT_WRITE);
+
+  do_relocations();
+
+  mprotect_cb((void*)aligned_relro_start,
+              aligned_relro_end - aligned_relro_start, PROT_READ);
+  // mprotect_cb and sysconf_cb are allocated in .bss, so we need to restore
+  // them to a NULL value.
+  mprotect_cb = NULL;
+  sysconf_cb = NULL;
+}
+
+__attribute__((section(".text._init_noinit_relro"))) int init_noinit_relro(
+    int argc, char** argv, char** env) {
+  do_relocations_with_relro();
+  return 0;
+}
+
+__attribute__((section(".text._init_relro"))) int init_relro(int argc,
+                                                             char** argv,
+                                                             char** env) {
+  do_relocations_with_relro();
+  original_init(argc, argv, env);
+  return 0;
+}
diff --git a/build/unix/elfhack/inject/copy_source.py b/build/unix/elfhack/inject/copy_source.py
new file mode 100644
index 0000000000..02b4f6237e
--- /dev/null
+++ b/build/unix/elfhack/inject/copy_source.py
@@ -0,0 +1,10 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+def copy(out_file, in_path):
+    with open(in_path, "r") as fh:
+        out_file.write(fh.read())
diff --git a/build/unix/elfhack/inject/moz.build b/build/unix/elfhack/inject/moz.build
new file mode 100644
index 0000000000..dfac1e1a00
--- /dev/null
+++ b/build/unix/elfhack/inject/moz.build
@@ -0,0 +1,40 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# dummy library name to avoid skipping building the source here, which
+# we only need the object for.
+Library("elfhack_inject")
+
+DIST_INSTALL = False
+
+cpu = CONFIG["CPU_ARCH"]
+
+gen_src = "%s.c" % cpu
+GeneratedFile(
+    gen_src, script="copy_source.py", entry_point="copy", inputs=["../inject.c"]
+)
+
+SOURCES += [
+    "!%s" % gen_src,
+]
+
+NO_PGO = True
+
+for v in ("OS_CPPFLAGS", "OS_CFLAGS", "DEBUG", "CLANG_PLUGIN", "OPTIMIZE", "FRAMEPTR"):
+    flags = []
+    idx = 0
+    for flag in COMPILE_FLAGS[v]:
+        if flag == "-isystem":
+            flags.append("".join(COMPILE_FLAGS[v][idx : idx + 2]))
+        elif flag.startswith(("-m", "-I", "-isystem")) or flag == "-fPIC":
+            flags.append(flag)
+        idx += 1
+    COMPILE_FLAGS[v] = flags
+
+COMPILE_FLAGS["OS_CFLAGS"] += ["-O2", "-fno-stack-protector", "-fno-lto"]
+
+AllowCompilerWarnings()
+NoVisibilityFlags()
diff --git a/build/unix/elfhack/moz.build b/build/unix/elfhack/moz.build
new file mode 100644
index 0000000000..7298f6c0cc
--- /dev/null
+++ b/build/unix/elfhack/moz.build
@@ -0,0 +1,34 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIST_INSTALL = False
+DIRS += ["inject"]
+
+if not CONFIG["CROSS_COMPILE"]:
+    SOURCES += [
+        "dummy.c",
+    ]
+    SOURCES["dummy.c"].flags += ["-fno-lto"]
+
+SOURCES += [
+    "test-array.c",
+    "test-ctors.c",
+]
+SOURCES["test-array.c"].flags += ["-fno-lto"]
+SOURCES["test-ctors.c"].flags += ["-fno-lto"]
+
+HOST_SOURCES += [
+    "elf.cpp",
+    "elfhack.cpp",
+]
+
+HostProgram("elfhack")
+
+NO_PGO = True
+
+COMPILE_FLAGS["OS_CXXFLAGS"] = [
+    f for f in COMPILE_FLAGS["OS_CXXFLAGS"] if f != "-fno-exceptions"
+] + ["-fexceptions"]
diff --git a/build/unix/elfhack/test-array.c b/build/unix/elfhack/test-array.c
new file mode 100644
index 0000000000..21aec3d360
--- /dev/null
+++ b/build/unix/elfhack/test-array.c
@@ -0,0 +1,8 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "test.c"
+
+__attribute__((section(".init_array"), used)) static void (*init_array[])() = {
+    end_test, test};
diff --git a/build/unix/elfhack/test-ctors.c b/build/unix/elfhack/test-ctors.c
new file mode 100644
index 0000000000..d082411e3d
--- /dev/null
+++ b/build/unix/elfhack/test-ctors.c
@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "test.c"
+
+/* Recent binutils would put .ctors content into a .init_array section */
+__attribute__((section(".manual_ctors"), used)) static void (*ctors[])() = {
+    (void (*)()) - 1, end_test, test, NULL};
+
+__attribute__((section(".init"))) void _init() {
+  void (**func)() = &ctors[sizeof(ctors) / sizeof(void (*)()) - 1];
+  while (*(--func) != (void (*)()) - 1) {
+    (*func)();
+  }
+}
diff --git a/build/unix/elfhack/test.c b/build/unix/elfhack/test.c
new file mode 100644
index 0000000000..a10833e521
--- /dev/null
+++ b/build/unix/elfhack/test.c
@@ -0,0 +1,199 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifdef DEF
+DEF(This)
+DEF(is)
+DEF(a)
+DEF(test)
+DEF(of)
+DEF(string)
+DEF(array)
+DEF(for)
+DEF(use)
+DEF(with)
+DEF(elfhack)
+DEF(to)
+DEF(see)
+DEF(whether)
+DEF(it)
+DEF(breaks)
+DEF(anything)
+DEF(but)
+DEF(one)
+DEF(needs)
+DEF(quite)
+DEF(some)
+DEF(strings)
+DEF(before)
+DEF(the)
+DEF(program)
+DEF(can)
+DEF(do)
+DEF(its)
+DEF(work)
+DEF(efficiently)
+DEF(Without)
+DEF(enough)
+DEF(data)
+DEF(relocation)
+DEF(sections)
+DEF(are)
+// clang-format off
+DEF(not)
+// clang-format on
+DEF(sufficiently)
+DEF(large)
+DEF(and)
+DEF(injected)
+DEF(code)
+DEF(wouldnt)
+DEF(fit)
+DEF(Said)
+DEF(otherwise)
+DEF(we)
+DEF(need)
+DEF(more)
+DEF(words)
+DEF(than)
+DEF(up)
+DEF(here)
+DEF(so)
+DEF(that)
+DEF(relocations)
+DEF(take)
+DEF(significant)
+DEF(bytes)
+DEF(amounts)
+DEF(which)
+DEF(isnt)
+DEF(exactly)
+DEF(easily)
+DEF(achieved)
+DEF(like)
+DEF(this)
+DEF(Actually)
+DEF(I)
+DEF(must)
+DEF(cheat)
+DEF(by)
+DEF(including)
+DEF(these)
+DEF(phrases)
+DEF(several)
+DEF(times)
+
+#else
+#  pragma GCC visibility push(default)
+#  include <stdlib.h>
+#  include <stdio.h>
+
+#  define DEF(w) static const char str_##w[] = #  w;
+#  include "test.c"
+#  undef DEF
+
+const char* strings[] = {
+#  define DEF(w) str_##w,
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+};
+
+/* Create a hole between two zones of relative relocations */
+int small_hole[] = {42, 42, 42, 42};
+
+const char* strings2[] = {
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+};
+
+/* Create a bigger hole between two zones of relative relocations */
+int bigger_hole[] = {
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+    42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
+};
+
+const char* strings3[] = {
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  undef DEF
+};
+
+static int ret = 1;
+
+int print_status() {
+  fprintf(stderr, "%s\n", ret ? "FAIL" : "PASS");
+  return ret;
+}
+
+/* On ARM, this creates a .tbss section before .init_array, which
+ * elfhack could then pick instead of .init_array.
+ * Also, when .tbss is big enough, elfhack may wrongfully consider
+ * following sections as part of the PT_TLS segment.
+ * Finally, gold makes TLS segments end on an aligned virtual address,
+ * even when the underlying section ends before that, and elfhack
+ * sanity checks may yield an error. */
+__thread int foo;
+__thread long long int bar[512];
+
+/* We need a .bss that can hold at least 2 pointers. The static in
+ * end_test() plus this variable should do. */
+size_t dummy;
+
+void end_test() {
+  static size_t count = 0;
+  /* Only exit when both constructors have been called */
+  if (++count == 2) {
+    ret = 0;
+    // Avoid the dummy variable being stripped out at link time because
+    // it's unused.
+    dummy = 1;
+  }
+}
+
+void test() {
+  int i = 0, j = 0, k = 0;
+#  define DEF_(a, i, w) \
+    if (a[i++] != str_##w) return;
+#  define DEF(w) DEF_(strings, i, w)
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  undef DEF
+#  define DEF(w) DEF_(strings2, j, w)
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  undef DEF
+#  define DEF(w) DEF_(strings3, k, w)
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  include "test.c"
+#  undef DEF
+  if (i != sizeof(strings) / sizeof(strings[0]) &&
+      j != sizeof(strings2) / sizeof(strings2[0]) &&
+      k != sizeof(strings3) / sizeof(strings3[0]))
+    fprintf(stderr, "WARNING: Test doesn't cover the whole array\n");
+  end_test();
+}
+
+#  pragma GCC visibility pop
+#endif