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/* 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 */
#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;
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;
Array<Phdr> phdrs(reinterpret_cast<const char*>(ehdr) + ehdr->e_phoff,
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;
dyn = &*phdr;
#ifdef __ARM_EABI__
/* We cannot initialize arm_exidx here
because we don't have a base yet */
arm_exidx_phdr = &*phdr;
/* 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 =
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)
DEBUG_LOG("LoadedElf::Create(\"%s\", %p) = %p", path, base_addr,
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]);
} break;
DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_STRTAB", uintptr_t(dyn->d_un.d_val));
DEBUG_LOG("%s 0x%08" PRIxPTR, "DT_SYMTAB", uintptr_t(dyn->d_un.d_val));
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;