| // Copyright (c) 2008, Google Inc. |
| // All rights reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following disclaimer |
| // in the documentation and/or other materials provided with the |
| // distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| // --- |
| // Author: Paul Pluzhnikov |
| // |
| // Allow dynamic symbol lookup in an in-memory Elf image. |
| // |
| |
| #include "base/elf_mem_image.h" |
| |
| #ifdef HAVE_ELF_MEM_IMAGE // defined in elf_mem_image.h |
| |
| #include <stddef.h> // for size_t, ptrdiff_t |
| #include "base/logging.h" |
| |
| // From binutils/include/elf/common.h (this doesn't appear to be documented |
| // anywhere else). |
| // |
| // /* This flag appears in a Versym structure. It means that the symbol |
| // is hidden, and is only visible with an explicit version number. |
| // This is a GNU extension. */ |
| // #define VERSYM_HIDDEN 0x8000 |
| // |
| // /* This is the mask for the rest of the Versym information. */ |
| // #define VERSYM_VERSION 0x7fff |
| |
| #define VERSYM_VERSION 0x7fff |
| |
| namespace base { |
| |
| namespace { |
| template <int N> class ElfClass { |
| public: |
| static const int kElfClass = -1; |
| static int ElfBind(const ElfW(Sym) *) { |
| CHECK(false); // << "Unexpected word size"; |
| return 0; |
| } |
| static int ElfType(const ElfW(Sym) *) { |
| CHECK(false); // << "Unexpected word size"; |
| return 0; |
| } |
| }; |
| |
| template <> class ElfClass<32> { |
| public: |
| static const int kElfClass = ELFCLASS32; |
| static int ElfBind(const ElfW(Sym) *symbol) { |
| return ELF32_ST_BIND(symbol->st_info); |
| } |
| static int ElfType(const ElfW(Sym) *symbol) { |
| return ELF32_ST_TYPE(symbol->st_info); |
| } |
| }; |
| |
| template <> class ElfClass<64> { |
| public: |
| static const int kElfClass = ELFCLASS64; |
| static int ElfBind(const ElfW(Sym) *symbol) { |
| return ELF64_ST_BIND(symbol->st_info); |
| } |
| static int ElfType(const ElfW(Sym) *symbol) { |
| return ELF64_ST_TYPE(symbol->st_info); |
| } |
| }; |
| |
| typedef ElfClass<__WORDSIZE> CurrentElfClass; |
| |
| // Extract an element from one of the ELF tables, cast it to desired type. |
| // This is just a simple arithmetic and a glorified cast. |
| // Callers are responsible for bounds checking. |
| template <class T> |
| const T* GetTableElement(const ElfW(Ehdr) *ehdr, |
| ElfW(Off) table_offset, |
| ElfW(Word) element_size, |
| size_t index) { |
| return reinterpret_cast<const T*>(reinterpret_cast<const char *>(ehdr) |
| + table_offset |
| + index * element_size); |
| } |
| } // namespace |
| |
| const void *const ElfMemImage::kInvalidBase = |
| reinterpret_cast<const void *>(~0L); |
| |
| ElfMemImage::ElfMemImage(const void *base) { |
| CHECK(base != kInvalidBase); |
| Init(base); |
| } |
| |
| int ElfMemImage::GetNumSymbols() const { |
| if (!hash_) { |
| return 0; |
| } |
| // See http://www.caldera.com/developers/gabi/latest/ch5.dynamic.html#hash |
| return hash_[1]; |
| } |
| |
| const ElfW(Sym) *ElfMemImage::GetDynsym(int index) const { |
| CHECK_LT(index, GetNumSymbols()); |
| return dynsym_ + index; |
| } |
| |
| const ElfW(Versym) *ElfMemImage::GetVersym(int index) const { |
| CHECK_LT(index, GetNumSymbols()); |
| return versym_ + index; |
| } |
| |
| const ElfW(Phdr) *ElfMemImage::GetPhdr(int index) const { |
| CHECK_LT(index, ehdr_->e_phnum); |
| return GetTableElement<ElfW(Phdr)>(ehdr_, |
| ehdr_->e_phoff, |
| ehdr_->e_phentsize, |
| index); |
| } |
| |
| const char *ElfMemImage::GetDynstr(ElfW(Word) offset) const { |
| CHECK_LT(offset, strsize_); |
| return dynstr_ + offset; |
| } |
| |
| const void *ElfMemImage::GetSymAddr(const ElfW(Sym) *sym) const { |
| if (sym->st_shndx == SHN_UNDEF || sym->st_shndx >= SHN_LORESERVE) { |
| // Symbol corresponds to "special" (e.g. SHN_ABS) section. |
| return reinterpret_cast<const void *>(sym->st_value); |
| } |
| CHECK_LT(link_base_, sym->st_value); |
| return GetTableElement<char>(ehdr_, 0, 1, sym->st_value) - link_base_; |
| } |
| |
| const ElfW(Verdef) *ElfMemImage::GetVerdef(int index) const { |
| CHECK_LE(index, verdefnum_); |
| const ElfW(Verdef) *version_definition = verdef_; |
| while (version_definition->vd_ndx < index && version_definition->vd_next) { |
| const char *const version_definition_as_char = |
| reinterpret_cast<const char *>(version_definition); |
| version_definition = |
| reinterpret_cast<const ElfW(Verdef) *>(version_definition_as_char + |
| version_definition->vd_next); |
| } |
| return version_definition->vd_ndx == index ? version_definition : NULL; |
| } |
| |
| const ElfW(Verdaux) *ElfMemImage::GetVerdefAux( |
| const ElfW(Verdef) *verdef) const { |
| return reinterpret_cast<const ElfW(Verdaux) *>(verdef+1); |
| } |
| |
| const char *ElfMemImage::GetVerstr(ElfW(Word) offset) const { |
| CHECK_LT(offset, strsize_); |
| return dynstr_ + offset; |
| } |
| |
| void ElfMemImage::Init(const void *base) { |
| ehdr_ = NULL; |
| dynsym_ = NULL; |
| dynstr_ = NULL; |
| versym_ = NULL; |
| verdef_ = NULL; |
| hash_ = NULL; |
| strsize_ = 0; |
| verdefnum_ = 0; |
| link_base_ = ~0L; // Sentinel: PT_LOAD .p_vaddr can't possibly be this. |
| if (!base) { |
| return; |
| } |
| const intptr_t base_as_uintptr_t = reinterpret_cast<uintptr_t>(base); |
| // Fake VDSO has low bit set. |
| const bool fake_vdso = ((base_as_uintptr_t & 1) != 0); |
| base = reinterpret_cast<const void *>(base_as_uintptr_t & ~1); |
| const char *const base_as_char = reinterpret_cast<const char *>(base); |
| if (base_as_char[EI_MAG0] != ELFMAG0 || base_as_char[EI_MAG1] != ELFMAG1 || |
| base_as_char[EI_MAG2] != ELFMAG2 || base_as_char[EI_MAG3] != ELFMAG3) { |
| RAW_DCHECK(false, "no ELF magic"); // at %p", base); |
| return; |
| } |
| int elf_class = base_as_char[EI_CLASS]; |
| if (elf_class != CurrentElfClass::kElfClass) { |
| DCHECK_EQ(elf_class, CurrentElfClass::kElfClass); |
| return; |
| } |
| switch (base_as_char[EI_DATA]) { |
| case ELFDATA2LSB: { |
| if (__LITTLE_ENDIAN != __BYTE_ORDER) { |
| DCHECK_EQ(__LITTLE_ENDIAN, __BYTE_ORDER); // << ": wrong byte order"; |
| return; |
| } |
| break; |
| } |
| case ELFDATA2MSB: { |
| if (__BIG_ENDIAN != __BYTE_ORDER) { |
| DCHECK_EQ(__BIG_ENDIAN, __BYTE_ORDER); // << ": wrong byte order"; |
| return; |
| } |
| break; |
| } |
| default: { |
| RAW_DCHECK(false, "unexpected data encoding"); // << base_as_char[EI_DATA]; |
| return; |
| } |
| } |
| |
| ehdr_ = reinterpret_cast<const ElfW(Ehdr) *>(base); |
| const ElfW(Phdr) *dynamic_program_header = NULL; |
| for (int i = 0; i < ehdr_->e_phnum; ++i) { |
| const ElfW(Phdr) *const program_header = GetPhdr(i); |
| switch (program_header->p_type) { |
| case PT_LOAD: |
| if (link_base_ == ~0L) { |
| link_base_ = program_header->p_vaddr; |
| } |
| break; |
| case PT_DYNAMIC: |
| dynamic_program_header = program_header; |
| break; |
| } |
| } |
| if (link_base_ == ~0L || !dynamic_program_header) { |
| RAW_DCHECK(~0L != link_base_, "no PT_LOADs in VDSO"); |
| RAW_DCHECK(dynamic_program_header, "no PT_DYNAMIC in VDSO"); |
| // Mark this image as not present. Can not recur infinitely. |
| Init(0); |
| return; |
| } |
| ptrdiff_t relocation = |
| base_as_char - reinterpret_cast<const char *>(link_base_); |
| ElfW(Dyn) *dynamic_entry = |
| reinterpret_cast<ElfW(Dyn) *>(dynamic_program_header->p_vaddr + |
| relocation); |
| for (; dynamic_entry->d_tag != DT_NULL; ++dynamic_entry) { |
| ElfW(Xword) value = dynamic_entry->d_un.d_val; |
| if (fake_vdso) { |
| // A complication: in the real VDSO, dynamic entries are not relocated |
| // (it wasn't loaded by a dynamic loader). But when testing with a |
| // "fake" dlopen()ed vdso library, the loader relocates some (but |
| // not all!) of them before we get here. |
| if (dynamic_entry->d_tag == DT_VERDEF) { |
| // The only dynamic entry (of the ones we care about) libc-2.3.6 |
| // loader doesn't relocate. |
| value += relocation; |
| } |
| } else { |
| // Real VDSO. Everything needs to be relocated. |
| value += relocation; |
| } |
| switch (dynamic_entry->d_tag) { |
| case DT_HASH: |
| hash_ = reinterpret_cast<ElfW(Word) *>(value); |
| break; |
| case DT_SYMTAB: |
| dynsym_ = reinterpret_cast<ElfW(Sym) *>(value); |
| break; |
| case DT_STRTAB: |
| dynstr_ = reinterpret_cast<const char *>(value); |
| break; |
| case DT_VERSYM: |
| versym_ = reinterpret_cast<ElfW(Versym) *>(value); |
| break; |
| case DT_VERDEF: |
| verdef_ = reinterpret_cast<ElfW(Verdef) *>(value); |
| break; |
| case DT_VERDEFNUM: |
| verdefnum_ = dynamic_entry->d_un.d_val; |
| break; |
| case DT_STRSZ: |
| strsize_ = dynamic_entry->d_un.d_val; |
| break; |
| default: |
| // Unrecognized entries explicitly ignored. |
| break; |
| } |
| } |
| if (!hash_ || !dynsym_ || !dynstr_ || !versym_ || |
| !verdef_ || !verdefnum_ || !strsize_) { |
| RAW_DCHECK(hash_, "invalid VDSO (no DT_HASH)"); |
| RAW_DCHECK(dynsym_, "invalid VDSO (no DT_SYMTAB)"); |
| RAW_DCHECK(dynstr_, "invalid VDSO (no DT_STRTAB)"); |
| RAW_DCHECK(versym_, "invalid VDSO (no DT_VERSYM)"); |
| RAW_DCHECK(verdef_, "invalid VDSO (no DT_VERDEF)"); |
| RAW_DCHECK(verdefnum_, "invalid VDSO (no DT_VERDEFNUM)"); |
| RAW_DCHECK(strsize_, "invalid VDSO (no DT_STRSZ)"); |
| // Mark this image as not present. Can not recur infinitely. |
| Init(0); |
| return; |
| } |
| } |
| |
| bool ElfMemImage::LookupSymbol(const char *name, |
| const char *version, |
| int type, |
| SymbolInfo *info) const { |
| for (SymbolIterator it = begin(); it != end(); ++it) { |
| if (strcmp(it->name, name) == 0 && strcmp(it->version, version) == 0 && |
| CurrentElfClass::ElfType(it->symbol) == type) { |
| if (info) { |
| *info = *it; |
| } |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| bool ElfMemImage::LookupSymbolByAddress(const void *address, |
| SymbolInfo *info_out) const { |
| for (SymbolIterator it = begin(); it != end(); ++it) { |
| const char *const symbol_start = |
| reinterpret_cast<const char *>(it->address); |
| const char *const symbol_end = symbol_start + it->symbol->st_size; |
| if (symbol_start <= address && address < symbol_end) { |
| if (info_out) { |
| // Client wants to know details for that symbol (the usual case). |
| if (CurrentElfClass::ElfBind(it->symbol) == STB_GLOBAL) { |
| // Strong symbol; just return it. |
| *info_out = *it; |
| return true; |
| } else { |
| // Weak or local. Record it, but keep looking for a strong one. |
| *info_out = *it; |
| } |
| } else { |
| // Client only cares if there is an overlapping symbol. |
| return true; |
| } |
| } |
| } |
| return false; |
| } |
| |
| ElfMemImage::SymbolIterator::SymbolIterator(const void *const image, int index) |
| : index_(index), image_(image) { |
| } |
| |
| const ElfMemImage::SymbolInfo *ElfMemImage::SymbolIterator::operator->() const { |
| return &info_; |
| } |
| |
| const ElfMemImage::SymbolInfo& ElfMemImage::SymbolIterator::operator*() const { |
| return info_; |
| } |
| |
| bool ElfMemImage::SymbolIterator::operator==(const SymbolIterator &rhs) const { |
| return this->image_ == rhs.image_ && this->index_ == rhs.index_; |
| } |
| |
| bool ElfMemImage::SymbolIterator::operator!=(const SymbolIterator &rhs) const { |
| return !(*this == rhs); |
| } |
| |
| ElfMemImage::SymbolIterator &ElfMemImage::SymbolIterator::operator++() { |
| this->Update(1); |
| return *this; |
| } |
| |
| ElfMemImage::SymbolIterator ElfMemImage::begin() const { |
| SymbolIterator it(this, 0); |
| it.Update(0); |
| return it; |
| } |
| |
| ElfMemImage::SymbolIterator ElfMemImage::end() const { |
| return SymbolIterator(this, GetNumSymbols()); |
| } |
| |
| void ElfMemImage::SymbolIterator::Update(int increment) { |
| const ElfMemImage *image = reinterpret_cast<const ElfMemImage *>(image_); |
| CHECK(image->IsPresent() || increment == 0); |
| if (!image->IsPresent()) { |
| return; |
| } |
| index_ += increment; |
| if (index_ >= image->GetNumSymbols()) { |
| index_ = image->GetNumSymbols(); |
| return; |
| } |
| const ElfW(Sym) *symbol = image->GetDynsym(index_); |
| const ElfW(Versym) *version_symbol = image->GetVersym(index_); |
| CHECK(symbol && version_symbol); |
| const char *const symbol_name = image->GetDynstr(symbol->st_name); |
| const ElfW(Versym) version_index = version_symbol[0] & VERSYM_VERSION; |
| const ElfW(Verdef) *version_definition = NULL; |
| const char *version_name = ""; |
| if (symbol->st_shndx == SHN_UNDEF) { |
| // Undefined symbols reference DT_VERNEED, not DT_VERDEF, and |
| // version_index could well be greater than verdefnum_, so calling |
| // GetVerdef(version_index) may trigger assertion. |
| } else { |
| version_definition = image->GetVerdef(version_index); |
| } |
| if (version_definition) { |
| // I am expecting 1 or 2 auxiliary entries: 1 for the version itself, |
| // optional 2nd if the version has a parent. |
| CHECK_LE(1, version_definition->vd_cnt); |
| CHECK_LE(version_definition->vd_cnt, 2); |
| const ElfW(Verdaux) *version_aux = image->GetVerdefAux(version_definition); |
| version_name = image->GetVerstr(version_aux->vda_name); |
| } |
| info_.name = symbol_name; |
| info_.version = version_name; |
| info_.address = image->GetSymAddr(symbol); |
| info_.symbol = symbol; |
| } |
| |
| } // namespace base |
| |
| #endif // HAVE_ELF_MEM_IMAGE |