Refactor ElfWriter and introduce ElfWriterQuick
Change-Id: I3eaa1fa1085bb4d28fe342a7420272720e48274b
diff --git a/src/elf_stripper.cc b/src/elf_stripper.cc
new file mode 100644
index 0000000..7fc662c
--- /dev/null
+++ b/src/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