From 43a97878ce14b72f0981164f87f2e35e14151312 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 11:22:09 +0200
Subject: Adding upstream version 110.0.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 build/unix/elfhack/elfhack.cpp | 1450 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 1450 insertions(+)
 create mode 100644 build/unix/elfhack/elfhack.cpp

(limited to 'build/unix/elfhack/elfhack.cpp')

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;
+}
-- 
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