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Diffstat (limited to 'compiler/elf_stripper.cc')
| -rw-r--r-- | compiler/elf_stripper.cc | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/compiler/elf_stripper.cc b/compiler/elf_stripper.cc new file mode 100644 index 000000000..7fc662ca1 --- /dev/null +++ b/compiler/elf_stripper.cc @@ -0,0 +1,129 @@ +/* + * Copyright (C) 2012 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#include "elf_stripper.h" + +#include <vector> + +#include <llvm/Support/ELF.h> + +#include "UniquePtr.h" +#include "base/logging.h" +#include "elf_file.h" +#include "utils.h" + +namespace art { + +bool ElfStripper::Strip(File* file) { + UniquePtr<ElfFile> elf_file(ElfFile::Open(file, true, false)); + CHECK(elf_file.get() != NULL); + + // ELF files produced by MCLinker look roughly like this + // + // +------------+ + // | Elf32_Ehdr | contains number of Elf32_Shdr and offset to first + // +------------+ + // | Elf32_Phdr | program headers + // | Elf32_Phdr | + // | ... | + // | Elf32_Phdr | + // +------------+ + // | section | mixture of needed and unneeded sections + // +------------+ + // | section | + // +------------+ + // | ... | + // +------------+ + // | section | + // +------------+ + // | Elf32_Shdr | section headers + // | Elf32_Shdr | + // | ... | contains offset to section start + // | Elf32_Shdr | + // +------------+ + // + // To strip: + // - leave the Elf32_Ehdr and Elf32_Phdr values in place. + // - walk the sections making a new set of Elf32_Shdr section headers for what we want to keep + // - move the sections are keeping up to fill in gaps of sections we want to strip + // - write new Elf32_Shdr section headers to end of file, updating Elf32_Ehdr + // - truncate rest of file + // + + std::vector<llvm::ELF::Elf32_Shdr> section_headers; + std::vector<llvm::ELF::Elf32_Word> section_headers_original_indexes; + section_headers.reserve(elf_file->GetSectionHeaderNum()); + + + llvm::ELF::Elf32_Shdr& string_section = elf_file->GetSectionNameStringSection(); + for (llvm::ELF::Elf32_Word i = 0; i < elf_file->GetSectionHeaderNum(); i++) { + llvm::ELF::Elf32_Shdr& sh = elf_file->GetSectionHeader(i); + const char* name = elf_file->GetString(string_section, sh.sh_name); + if (name == NULL) { + CHECK_EQ(0U, i); + section_headers.push_back(sh); + section_headers_original_indexes.push_back(0); + continue; + } + if (StartsWith(name, ".debug") + || (strcmp(name, ".strtab") == 0) + || (strcmp(name, ".symtab") == 0)) { + continue; + } + section_headers.push_back(sh); + section_headers_original_indexes.push_back(i); + } + CHECK_NE(0U, section_headers.size()); + CHECK_EQ(section_headers.size(), section_headers_original_indexes.size()); + + // section 0 is the NULL section, sections start at offset of first section + llvm::ELF::Elf32_Off offset = elf_file->GetSectionHeader(1).sh_offset; + for (size_t i = 1; i < section_headers.size(); i++) { + llvm::ELF::Elf32_Shdr& new_sh = section_headers[i]; + llvm::ELF::Elf32_Shdr& old_sh = elf_file->GetSectionHeader(section_headers_original_indexes[i]); + CHECK_EQ(new_sh.sh_name, old_sh.sh_name); + if (old_sh.sh_addralign > 1) { + offset = RoundUp(offset, old_sh.sh_addralign); + } + if (old_sh.sh_offset == offset) { + // already in place + offset += old_sh.sh_size; + continue; + } + // shift section earlier + memmove(elf_file->Begin() + offset, + elf_file->Begin() + old_sh.sh_offset, + old_sh.sh_size); + new_sh.sh_offset = offset; + offset += old_sh.sh_size; + } + + llvm::ELF::Elf32_Off shoff = offset; + size_t section_headers_size_in_bytes = section_headers.size() * sizeof(llvm::ELF::Elf32_Shdr); + memcpy(elf_file->Begin() + offset, §ion_headers[0], section_headers_size_in_bytes); + offset += section_headers_size_in_bytes; + + elf_file->GetHeader().e_shnum = section_headers.size(); + elf_file->GetHeader().e_shoff = shoff; + int result = ftruncate(file->Fd(), offset); + if (result != 0) { + PLOG(ERROR) << "Failed to truncate while stripping ELF file: " << file->GetPath(); + return false; + } + return true; +} + +} // namespace art |