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Diffstat (limited to 'mozglue/linker/BaseElf.cpp')
| -rw-r--r-- | mozglue/linker/BaseElf.cpp | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/mozglue/linker/BaseElf.cpp b/mozglue/linker/BaseElf.cpp new file mode 100644 index 0000000000..78542b3875 --- /dev/null +++ b/mozglue/linker/BaseElf.cpp @@ -0,0 +1,190 @@ +/* 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 "BaseElf.h" +#include "Elfxx.h" +#include "Logging.h" +#include "mozilla/IntegerPrintfMacros.h" +#include "mozilla/RefPtr.h" + +using namespace Elf; + +unsigned long BaseElf::Hash(const char* symbol) { + const unsigned char* sym = reinterpret_cast<const unsigned char*>(symbol); + unsigned long h = 0, g; + while (*sym) { + h = (h << 4) + *sym++; + g = h & 0xf0000000; + h ^= g; + h ^= g >> 24; + } + return h; +} + +void* BaseElf::GetSymbolPtr(const char* symbol) const { + return GetSymbolPtr(symbol, Hash(symbol)); +} + +void* BaseElf::GetSymbolPtr(const char* symbol, unsigned long hash) const { + const Sym* sym = GetSymbol(symbol, hash); + void* ptr = nullptr; + if (sym && sym->st_shndx != SHN_UNDEF) ptr = GetPtr(sym->st_value); + DEBUG_LOG("BaseElf::GetSymbolPtr(%p [\"%s\"], \"%s\") = %p", + reinterpret_cast<const void*>(this), GetPath(), symbol, ptr); + return ptr; +} + +const Sym* BaseElf::GetSymbol(const char* symbol, unsigned long hash) const { + /* Search symbol with the buckets and chains tables. + * The hash computed from the symbol name gives an index in the buckets + * table. The corresponding value in the bucket table is an index in the + * symbols table and in the chains table. + * If the corresponding symbol in the symbols table matches, we're done. + * Otherwise, the corresponding value in the chains table is a new index + * in both tables, which corresponding symbol is tested and so on and so + * forth */ + size_t bucket = hash % buckets.numElements(); + for (size_t y = buckets[bucket]; y != STN_UNDEF; y = chains[y]) { + if (strcmp(symbol, strtab.GetStringAt(symtab[y].st_name))) continue; + return &symtab[y]; + } + return nullptr; +} + +bool BaseElf::Contains(void* addr) const { return base.Contains(addr); } + +#ifdef __ARM_EABI__ +const void* BaseElf::FindExidx(int* pcount) const { + if (arm_exidx) { + *pcount = arm_exidx.numElements(); + return arm_exidx; + } + *pcount = 0; + return nullptr; +} +#endif + +already_AddRefed<LibHandle> LoadedElf::Create(const char* path, + void* base_addr) { + DEBUG_LOG("LoadedElf::Create(\"%s\", %p) = ...", path, base_addr); + + uint8_t mapped; + /* If the page is not mapped, mincore returns an error. If base_addr is + * nullptr, as would happen if the corresponding binary is prelinked with + * the prelink look (but not with the android apriori tool), no page being + * mapped there (right?), mincore returns an error, too, which makes + * prelinked libraries on glibc unsupported. This is not an interesting + * use case for now, so don't try supporting that case. + */ + if (mincore(const_cast<void*>(base_addr), PageSize(), &mapped)) + return nullptr; + + RefPtr<LoadedElf> elf = new LoadedElf(path); + + const Ehdr* ehdr = Ehdr::validate(base_addr); + if (!ehdr) return nullptr; + + Addr min_vaddr = (Addr)-1; // We want to find the lowest and biggest + Addr max_vaddr = 0; // virtual address used by this Elf. + const Phdr* dyn = nullptr; +#ifdef __ARM_EABI__ + const Phdr* arm_exidx_phdr = nullptr; +#endif + + Array<Phdr> phdrs(reinterpret_cast<const char*>(ehdr) + ehdr->e_phoff, + ehdr->e_phnum); + for (auto phdr = phdrs.begin(); phdr < phdrs.end(); ++phdr) { + switch (phdr->p_type) { + case PT_LOAD: + if (phdr->p_vaddr < min_vaddr) min_vaddr = phdr->p_vaddr; + if (max_vaddr < phdr->p_vaddr + phdr->p_memsz) + max_vaddr = phdr->p_vaddr + phdr->p_memsz; + break; + case PT_DYNAMIC: + dyn = &*phdr; + break; +#ifdef __ARM_EABI__ + case PT_ARM_EXIDX: + /* We cannot initialize arm_exidx here + because we don't have a base yet */ + arm_exidx_phdr = &*phdr; + break; +#endif + } + } + + /* If the lowest PT_LOAD virtual address in headers is not 0, then the ELF + * is either prelinked or a non-PIE executable. The former case is not + * possible, because base_addr would be nullptr and the mincore test above + * would already have made us return. + * For a non-PIE executable, PT_LOADs contain absolute addresses, so in + * practice, this means min_vaddr should be equal to base_addr. max_vaddr + * can thus be adjusted accordingly. + */ + if (min_vaddr != 0) { + void* min_vaddr_ptr = + reinterpret_cast<void*>(static_cast<uintptr_t>(min_vaddr)); + if (min_vaddr_ptr != base_addr) { + LOG("%s: %p != %p", elf->GetPath(), min_vaddr_ptr, base_addr); + return nullptr; + } + max_vaddr -= min_vaddr; + } + if (!dyn) { + LOG("%s: No PT_DYNAMIC segment found", elf->GetPath()); + return nullptr; + } + + elf->base.Assign(base_addr, max_vaddr); + + if (!elf->InitDyn(dyn)) return nullptr; + +#ifdef __ARM_EABI__ + if (arm_exidx_phdr) + elf->arm_exidx.InitSize(elf->GetPtr(arm_exidx_phdr->p_vaddr), + arm_exidx_phdr->p_memsz); +#endif + + DEBUG_LOG("LoadedElf::Create(\"%s\", %p) = %p", path, base_addr, + static_cast<void*>(elf)); + + ElfLoader::Singleton.Register(elf); + return elf.forget(); +} + +bool LoadedElf::InitDyn(const Phdr* pt_dyn) { + Array<Dyn> dyns; + dyns.InitSize(GetPtr<Dyn>(pt_dyn->p_vaddr), pt_dyn->p_filesz); + + size_t symnum = 0; + for (auto dyn = dyns.begin(); dyn < dyns.end() && dyn->d_tag; ++dyn) { + switch (dyn->d_tag) { + case DT_HASH: { + DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_HASH", uintptr_t(dyn->d_un.d_val)); + const Elf::Word* hash_table_header = GetPtr<Elf::Word>(dyn->d_un.d_ptr); + symnum = hash_table_header[1]; + buckets.Init(&hash_table_header[2], hash_table_header[0]); + chains.Init(&*buckets.end()); + } break; + case DT_STRTAB: + DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_STRTAB", uintptr_t(dyn->d_un.d_val)); + strtab.Init(GetPtr(dyn->d_un.d_ptr)); + break; + case DT_SYMTAB: + DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_SYMTAB", uintptr_t(dyn->d_un.d_val)); + symtab.Init(GetPtr(dyn->d_un.d_ptr)); + break; + } + } + if (!buckets || !symnum) { + ERROR("%s: Missing or broken DT_HASH", GetPath()); + } else if (!strtab) { + ERROR("%s: Missing DT_STRTAB", GetPath()); + } else if (!symtab) { + ERROR("%s: Missing DT_SYMTAB", GetPath()); + } else { + return true; + } + return false; +} |