| // Copyright 2014 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "crazy_linker_elf_symbols.h" |
| |
| #include "crazy_linker_debug.h" |
| #include "crazy_linker_elf_view.h" |
| |
| namespace crazy { |
| |
| namespace { |
| |
| // Compute the ELF hash of a given symbol. |
| unsigned ElfHash(const char* name) { |
| const uint8_t* ptr = reinterpret_cast<const uint8_t*>(name); |
| unsigned h = 0; |
| while (*ptr) { |
| h = (h << 4) + *ptr++; |
| unsigned g = h & 0xf0000000; |
| h ^= g; |
| h ^= g >> 24; |
| } |
| return h; |
| } |
| |
| } // namespace |
| |
| bool ElfSymbols::Init(const ElfView* view) { |
| LOG("%s: Parsing dynamic table\n", __FUNCTION__); |
| ElfView::DynamicIterator dyn(view); |
| for (; dyn.HasNext(); dyn.GetNext()) { |
| uintptr_t dyn_addr = dyn.GetAddress(view->load_bias()); |
| switch (dyn.GetTag()) { |
| case DT_HASH: |
| LOG(" DT_HASH addr=%p\n", dyn_addr); |
| { |
| ELF::Word* data = reinterpret_cast<ELF::Word*>(dyn_addr); |
| hash_bucket_size_ = data[0]; |
| hash_chain_size_ = data[1]; |
| hash_bucket_ = data + 2; |
| hash_chain_ = data + 2 + hash_bucket_size_; |
| } |
| break; |
| case DT_STRTAB: |
| LOG(" DT_STRTAB addr=%p\n", dyn_addr); |
| string_table_ = reinterpret_cast<const char*>(dyn_addr); |
| break; |
| case DT_SYMTAB: |
| LOG(" DT_SYMTAB addr=%p\n", dyn_addr); |
| symbol_table_ = reinterpret_cast<const ELF::Sym*>(dyn_addr); |
| break; |
| default: |
| ; |
| } |
| } |
| if (symbol_table_ == NULL || string_table_ == NULL || hash_bucket_ == NULL) |
| return false; |
| |
| return true; |
| } |
| |
| const ELF::Sym* ElfSymbols::LookupByAddress(void* address, |
| size_t load_bias) const { |
| ELF::Addr elf_addr = |
| reinterpret_cast<ELF::Addr>(address) - static_cast<ELF::Addr>(load_bias); |
| |
| for (size_t n = 0; n < hash_chain_size_; ++n) { |
| const ELF::Sym* sym = &symbol_table_[n]; |
| if (sym->st_shndx != SHN_UNDEF && elf_addr >= sym->st_value && |
| elf_addr < sym->st_value + sym->st_size) { |
| return sym; |
| } |
| } |
| return NULL; |
| } |
| |
| bool ElfSymbols::LookupNearestByAddress(void* address, |
| size_t load_bias, |
| const char** sym_name, |
| void** sym_addr, |
| size_t* sym_size) const { |
| ELF::Addr elf_addr = |
| reinterpret_cast<ELF::Addr>(address) - static_cast<ELF::Addr>(load_bias); |
| |
| const ELF::Sym* nearest_sym = NULL; |
| size_t nearest_diff = ~size_t(0); |
| |
| for (size_t n = 0; n < hash_chain_size_; ++n) { |
| const ELF::Sym* sym = &symbol_table_[n]; |
| if (sym->st_shndx == SHN_UNDEF) |
| continue; |
| |
| if (elf_addr >= sym->st_value && elf_addr < sym->st_value + sym->st_size) { |
| // This is a perfect match. |
| nearest_sym = sym; |
| break; |
| } |
| |
| // Otherwise, compute distance. |
| size_t diff; |
| if (elf_addr < sym->st_value) |
| diff = sym->st_value - elf_addr; |
| else |
| diff = elf_addr - sym->st_value - sym->st_size; |
| |
| if (diff < nearest_diff) { |
| nearest_sym = sym; |
| nearest_diff = diff; |
| } |
| } |
| |
| if (!nearest_sym) |
| return false; |
| |
| *sym_name = string_table_ + nearest_sym->st_name; |
| *sym_addr = reinterpret_cast<void*>(nearest_sym->st_value + load_bias); |
| *sym_size = nearest_sym->st_size; |
| return true; |
| } |
| |
| const ELF::Sym* ElfSymbols::LookupByName(const char* symbol_name) const { |
| unsigned hash = ElfHash(symbol_name); |
| |
| for (unsigned n = hash_bucket_[hash % hash_bucket_size_]; n != 0; |
| n = hash_chain_[n]) { |
| const ELF::Sym* symbol = &symbol_table_[n]; |
| // Check that the symbol has the appropriate name. |
| if (strcmp(string_table_ + symbol->st_name, symbol_name)) |
| continue; |
| // Ignore undefined symbols. |
| if (symbol->st_shndx == SHN_UNDEF) |
| continue; |
| // Ignore anything that isn't a global or weak definition. |
| switch (ELF_ST_BIND(symbol->st_info)) { |
| case STB_GLOBAL: |
| case STB_WEAK: |
| return symbol; |
| default: |
| ; |
| } |
| } |
| return NULL; |
| } |
| |
| } // namespace crazy |