139 lines
4.5 KiB
C++
139 lines
4.5 KiB
C++
/*
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* Copyright (C) 2012 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "elf_stripper.h"
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#include <unistd.h>
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#include <sys/types.h>
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#include <memory>
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#include <vector>
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#include "base/logging.h"
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#include "base/stringprintf.h"
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#include "elf_file.h"
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#include "elf_utils.h"
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#include "utils.h"
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namespace art {
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bool ElfStripper::Strip(File* file, std::string* error_msg) {
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std::unique_ptr<ElfFile> elf_file(ElfFile::Open(file, true, false, error_msg));
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if (elf_file.get() == nullptr) {
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return false;
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}
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// ELF files produced by MCLinker look roughly like this
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//
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// +------------+
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// | Elf32_Ehdr | contains number of Elf32_Shdr and offset to first
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// +------------+
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// | Elf32_Phdr | program headers
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// | Elf32_Phdr |
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// | ... |
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// | Elf32_Phdr |
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// +------------+
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// | section | mixture of needed and unneeded sections
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// +------------+
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// | section |
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// +------------+
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// | ... |
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// +------------+
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// | section |
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// +------------+
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// | Elf32_Shdr | section headers
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// | Elf32_Shdr |
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// | ... | contains offset to section start
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// | Elf32_Shdr |
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// +------------+
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//
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// To strip:
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// - leave the Elf32_Ehdr and Elf32_Phdr values in place.
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// - walk the sections making a new set of Elf32_Shdr section headers for what we want to keep
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// - move the sections are keeping up to fill in gaps of sections we want to strip
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// - write new Elf32_Shdr section headers to end of file, updating Elf32_Ehdr
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// - truncate rest of file
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//
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std::vector<Elf32_Shdr> section_headers;
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std::vector<Elf32_Word> section_headers_original_indexes;
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section_headers.reserve(elf_file->GetSectionHeaderNum());
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Elf32_Shdr* string_section = elf_file->GetSectionNameStringSection();
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CHECK(string_section != nullptr);
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for (Elf32_Word i = 0; i < elf_file->GetSectionHeaderNum(); i++) {
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Elf32_Shdr* sh = elf_file->GetSectionHeader(i);
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CHECK(sh != nullptr);
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const char* name = elf_file->GetString(*string_section, sh->sh_name);
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if (name == nullptr) {
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CHECK_EQ(0U, i);
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section_headers.push_back(*sh);
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section_headers_original_indexes.push_back(0);
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continue;
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}
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if (StartsWith(name, ".debug")
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|| (strcmp(name, ".strtab") == 0)
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|| (strcmp(name, ".symtab") == 0)) {
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continue;
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}
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section_headers.push_back(*sh);
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section_headers_original_indexes.push_back(i);
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}
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CHECK_NE(0U, section_headers.size());
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CHECK_EQ(section_headers.size(), section_headers_original_indexes.size());
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// section 0 is the NULL section, sections start at offset of first section
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CHECK(elf_file->GetSectionHeader(1) != nullptr);
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Elf32_Off offset = elf_file->GetSectionHeader(1)->sh_offset;
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for (size_t i = 1; i < section_headers.size(); i++) {
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Elf32_Shdr& new_sh = section_headers[i];
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Elf32_Shdr* old_sh = elf_file->GetSectionHeader(section_headers_original_indexes[i]);
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CHECK(old_sh != nullptr);
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CHECK_EQ(new_sh.sh_name, old_sh->sh_name);
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if (old_sh->sh_addralign > 1) {
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offset = RoundUp(offset, old_sh->sh_addralign);
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}
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if (old_sh->sh_offset == offset) {
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// already in place
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offset += old_sh->sh_size;
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continue;
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}
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// shift section earlier
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memmove(elf_file->Begin() + offset,
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elf_file->Begin() + old_sh->sh_offset,
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old_sh->sh_size);
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new_sh.sh_offset = offset;
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offset += old_sh->sh_size;
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}
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Elf32_Off shoff = offset;
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size_t section_headers_size_in_bytes = section_headers.size() * sizeof(Elf32_Shdr);
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memcpy(elf_file->Begin() + offset, §ion_headers[0], section_headers_size_in_bytes);
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offset += section_headers_size_in_bytes;
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elf_file->GetHeader().e_shnum = section_headers.size();
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elf_file->GetHeader().e_shoff = shoff;
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int result = ftruncate(file->Fd(), offset);
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if (result != 0) {
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*error_msg = StringPrintf("Failed to truncate while stripping ELF file: '%s': %s",
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file->GetPath().c_str(), strerror(errno));
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return false;
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}
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return true;
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}
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} // namespace art
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