Import relocation packer from chromium repo
Bug: 18051137
Change-Id: Ia67fa11da8247e3f86f70a8ce99e6695f2c05423
diff --git a/tools/relocation_packer/src/elf_file.cc b/tools/relocation_packer/src/elf_file.cc
new file mode 100644
index 0000000..3ffccec
--- /dev/null
+++ b/tools/relocation_packer/src/elf_file.cc
@@ -0,0 +1,1283 @@
+// 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.
+
+// Implementation notes:
+//
+// We need to remove a piece from the ELF shared library. However, we also
+// want to ensure that code and data loads at the same addresses as before
+// packing, so that tools like breakpad can still match up addresses found
+// in any crash dumps with data extracted from the pre-packed version of
+// the shared library.
+//
+// Arranging this means that we have to split one of the LOAD segments into
+// two. Unfortunately, the program headers are located at the very start
+// of the shared library file, so expanding the program header section
+// would cause a lot of consequent changes to files offsets that we don't
+// really want to have to handle.
+//
+// Luckily, though, there is a segment that is always present and always
+// unused on Android; the GNU_STACK segment. What we do is to steal that
+// and repurpose it to be one of the split LOAD segments. We then have to
+// sort LOAD segments by offset to keep the crazy linker happy.
+//
+// All of this takes place in SplitProgramHeadersForHole(), used on packing,
+// and is unraveled on unpacking in CoalesceProgramHeadersForHole(). See
+// commentary on those functions for an example of this segment stealing
+// in action.
+
+#include "elf_file.h"
+
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <algorithm>
+#include <string>
+#include <vector>
+
+#include "debug.h"
+#include "elf_traits.h"
+#include "libelf.h"
+#include "packer.h"
+
+namespace relocation_packer {
+
+// Stub identifier written to 'null out' packed data, "NULL".
+static const uint32_t kStubIdentifier = 0x4c4c554eu;
+
+// Out-of-band dynamic tags used to indicate the offset and size of the
+// android packed relocations section.
+static const ELF::Sword DT_ANDROID_REL_OFFSET = DT_LOOS;
+static const ELF::Sword DT_ANDROID_REL_SIZE = DT_LOOS + 1;
+
+// Alignment to preserve, in bytes. This must be at least as large as the
+// largest d_align and sh_addralign values found in the loaded file.
+// Out of caution for RELRO page alignment, we preserve to a complete target
+// page. See http://www.airs.com/blog/archives/189.
+static const size_t kPreserveAlignment = 4096;
+
+namespace {
+
+// Get section data. Checks that the section has exactly one data entry,
+// so that the section size and the data size are the same. True in
+// practice for all sections we resize when packing or unpacking. Done
+// by ensuring that a call to elf_getdata(section, data) returns NULL as
+// the next data entry.
+Elf_Data* GetSectionData(Elf_Scn* section) {
+ Elf_Data* data = elf_getdata(section, NULL);
+ CHECK(data && elf_getdata(section, data) == NULL);
+ return data;
+}
+
+// Rewrite section data. Allocates new data and makes it the data element's
+// buffer. Relies on program exit to free allocated data.
+void RewriteSectionData(Elf_Scn* section,
+ const void* section_data,
+ size_t size) {
+ Elf_Data* data = GetSectionData(section);
+ CHECK(size == data->d_size);
+ uint8_t* area = new uint8_t[size];
+ memcpy(area, section_data, size);
+ data->d_buf = area;
+}
+
+// Verbose ELF header logging.
+void VerboseLogElfHeader(const ELF::Ehdr* elf_header) {
+ VLOG(1) << "e_phoff = " << elf_header->e_phoff;
+ VLOG(1) << "e_shoff = " << elf_header->e_shoff;
+ VLOG(1) << "e_ehsize = " << elf_header->e_ehsize;
+ VLOG(1) << "e_phentsize = " << elf_header->e_phentsize;
+ VLOG(1) << "e_phnum = " << elf_header->e_phnum;
+ VLOG(1) << "e_shnum = " << elf_header->e_shnum;
+ VLOG(1) << "e_shstrndx = " << elf_header->e_shstrndx;
+}
+
+// Verbose ELF program header logging.
+void VerboseLogProgramHeader(size_t program_header_index,
+ const ELF::Phdr* program_header) {
+ std::string type;
+ switch (program_header->p_type) {
+ case PT_NULL: type = "NULL"; break;
+ case PT_LOAD: type = "LOAD"; break;
+ case PT_DYNAMIC: type = "DYNAMIC"; break;
+ case PT_INTERP: type = "INTERP"; break;
+ case PT_PHDR: type = "PHDR"; break;
+ case PT_GNU_RELRO: type = "GNU_RELRO"; break;
+ case PT_GNU_STACK: type = "GNU_STACK"; break;
+ case PT_ARM_EXIDX: type = "EXIDX"; break;
+ default: type = "(OTHER)"; break;
+ }
+ VLOG(1) << "phdr[" << program_header_index << "] : " << type;
+ VLOG(1) << " p_offset = " << program_header->p_offset;
+ VLOG(1) << " p_vaddr = " << program_header->p_vaddr;
+ VLOG(1) << " p_paddr = " << program_header->p_paddr;
+ VLOG(1) << " p_filesz = " << program_header->p_filesz;
+ VLOG(1) << " p_memsz = " << program_header->p_memsz;
+ VLOG(1) << " p_flags = " << program_header->p_flags;
+ VLOG(1) << " p_align = " << program_header->p_align;
+}
+
+// Verbose ELF section header logging.
+void VerboseLogSectionHeader(const std::string& section_name,
+ const ELF::Shdr* section_header) {
+ VLOG(1) << "section " << section_name;
+ VLOG(1) << " sh_addr = " << section_header->sh_addr;
+ VLOG(1) << " sh_offset = " << section_header->sh_offset;
+ VLOG(1) << " sh_size = " << section_header->sh_size;
+ VLOG(1) << " sh_addralign = " << section_header->sh_addralign;
+}
+
+// Verbose ELF section data logging.
+void VerboseLogSectionData(const Elf_Data* data) {
+ VLOG(1) << " data";
+ VLOG(1) << " d_buf = " << data->d_buf;
+ VLOG(1) << " d_off = " << data->d_off;
+ VLOG(1) << " d_size = " << data->d_size;
+ VLOG(1) << " d_align = " << data->d_align;
+}
+
+} // namespace
+
+// Load the complete ELF file into a memory image in libelf, and identify
+// the .rel.dyn or .rela.dyn, .dynamic, and .android.rel.dyn or
+// .android.rela.dyn sections. No-op if the ELF file has already been loaded.
+bool ElfFile::Load() {
+ if (elf_)
+ return true;
+
+ Elf* elf = elf_begin(fd_, ELF_C_RDWR, NULL);
+ CHECK(elf);
+
+ if (elf_kind(elf) != ELF_K_ELF) {
+ LOG(ERROR) << "File not in ELF format";
+ return false;
+ }
+
+ ELF::Ehdr* elf_header = ELF::getehdr(elf);
+ if (!elf_header) {
+ LOG(ERROR) << "Failed to load ELF header: " << elf_errmsg(elf_errno());
+ return false;
+ }
+ if (elf_header->e_machine != ELF::kMachine) {
+ LOG(ERROR) << "ELF file architecture is not " << ELF::Machine();
+ return false;
+ }
+ if (elf_header->e_type != ET_DYN) {
+ LOG(ERROR) << "ELF file is not a shared object";
+ return false;
+ }
+
+ // Require that our endianness matches that of the target, and that both
+ // are little-endian. Safe for all current build/target combinations.
+ const int endian = elf_header->e_ident[EI_DATA];
+ CHECK(endian == ELFDATA2LSB);
+ CHECK(__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__);
+
+ // Also require that the file class is as expected.
+ const int file_class = elf_header->e_ident[EI_CLASS];
+ CHECK(file_class == ELF::kFileClass);
+
+ VLOG(1) << "endian = " << endian << ", file class = " << file_class;
+ VerboseLogElfHeader(elf_header);
+
+ const ELF::Phdr* elf_program_header = ELF::getphdr(elf);
+ CHECK(elf_program_header);
+
+ const ELF::Phdr* dynamic_program_header = NULL;
+ for (size_t i = 0; i < elf_header->e_phnum; ++i) {
+ const ELF::Phdr* program_header = &elf_program_header[i];
+ VerboseLogProgramHeader(i, program_header);
+
+ if (program_header->p_type == PT_DYNAMIC) {
+ CHECK(dynamic_program_header == NULL);
+ dynamic_program_header = program_header;
+ }
+ }
+ CHECK(dynamic_program_header != NULL);
+
+ size_t string_index;
+ elf_getshdrstrndx(elf, &string_index);
+
+ // Notes of the dynamic relocations, packed relocations, and .dynamic
+ // sections. Found while iterating sections, and later stored in class
+ // attributes.
+ Elf_Scn* found_relocations_section = NULL;
+ Elf_Scn* found_android_relocations_section = NULL;
+ Elf_Scn* found_dynamic_section = NULL;
+
+ // Notes of relocation section types seen. We require one or the other of
+ // these; both is unsupported.
+ bool has_rel_relocations = false;
+ bool has_rela_relocations = false;
+
+ Elf_Scn* section = NULL;
+ while ((section = elf_nextscn(elf, section)) != NULL) {
+ const ELF::Shdr* section_header = ELF::getshdr(section);
+ std::string name = elf_strptr(elf, string_index, section_header->sh_name);
+ VerboseLogSectionHeader(name, section_header);
+
+ // Note relocation section types.
+ if (section_header->sh_type == SHT_REL) {
+ has_rel_relocations = true;
+ }
+ if (section_header->sh_type == SHT_RELA) {
+ has_rela_relocations = true;
+ }
+
+ // Note special sections as we encounter them.
+ if ((name == ".rel.dyn" || name == ".rela.dyn") &&
+ section_header->sh_size > 0) {
+ found_relocations_section = section;
+ }
+ if ((name == ".android.rel.dyn" || name == ".android.rela.dyn") &&
+ section_header->sh_size > 0) {
+ found_android_relocations_section = section;
+ }
+ if (section_header->sh_offset == dynamic_program_header->p_offset) {
+ found_dynamic_section = section;
+ }
+
+ // Ensure we preserve alignment, repeated later for the data block(s).
+ CHECK(section_header->sh_addralign <= kPreserveAlignment);
+
+ Elf_Data* data = NULL;
+ while ((data = elf_getdata(section, data)) != NULL) {
+ CHECK(data->d_align <= kPreserveAlignment);
+ VerboseLogSectionData(data);
+ }
+ }
+
+ // Loading failed if we did not find the required special sections.
+ if (!found_relocations_section) {
+ LOG(ERROR) << "Missing or empty .rel.dyn or .rela.dyn section";
+ return false;
+ }
+ if (!found_android_relocations_section) {
+ LOG(ERROR) << "Missing or empty .android.rel.dyn or .android.rela.dyn "
+ << "section (to fix, run with --help and follow the "
+ << "pre-packing instructions)";
+ return false;
+ }
+ if (!found_dynamic_section) {
+ LOG(ERROR) << "Missing .dynamic section";
+ return false;
+ }
+
+ // Loading failed if we could not identify the relocations type.
+ if (!has_rel_relocations && !has_rela_relocations) {
+ LOG(ERROR) << "No relocations sections found";
+ return false;
+ }
+ if (has_rel_relocations && has_rela_relocations) {
+ LOG(ERROR) << "Multiple relocations sections with different types found, "
+ << "not currently supported";
+ return false;
+ }
+
+ elf_ = elf;
+ relocations_section_ = found_relocations_section;
+ dynamic_section_ = found_dynamic_section;
+ android_relocations_section_ = found_android_relocations_section;
+ relocations_type_ = has_rel_relocations ? REL : RELA;
+ return true;
+}
+
+namespace {
+
+// Helper for ResizeSection(). Adjust the main ELF header for the hole.
+void AdjustElfHeaderForHole(ELF::Ehdr* elf_header,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ if (elf_header->e_phoff > hole_start) {
+ elf_header->e_phoff += hole_size;
+ VLOG(1) << "e_phoff adjusted to " << elf_header->e_phoff;
+ }
+ if (elf_header->e_shoff > hole_start) {
+ elf_header->e_shoff += hole_size;
+ VLOG(1) << "e_shoff adjusted to " << elf_header->e_shoff;
+ }
+}
+
+// Helper for ResizeSection(). Adjust all section headers for the hole.
+void AdjustSectionHeadersForHole(Elf* elf,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ size_t string_index;
+ elf_getshdrstrndx(elf, &string_index);
+
+ Elf_Scn* section = NULL;
+ while ((section = elf_nextscn(elf, section)) != NULL) {
+ ELF::Shdr* section_header = ELF::getshdr(section);
+ std::string name = elf_strptr(elf, string_index, section_header->sh_name);
+
+ if (section_header->sh_offset > hole_start) {
+ section_header->sh_offset += hole_size;
+ VLOG(1) << "section " << name
+ << " sh_offset adjusted to " << section_header->sh_offset;
+ }
+ }
+}
+
+// Helper for ResizeSection(). Adjust the offsets of any program headers
+// that have offsets currently beyond the hole start.
+void AdjustProgramHeaderOffsets(ELF::Phdr* program_headers,
+ size_t count,
+ ELF::Phdr* ignored_1,
+ ELF::Phdr* ignored_2,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ for (size_t i = 0; i < count; ++i) {
+ ELF::Phdr* program_header = &program_headers[i];
+
+ if (program_header == ignored_1 || program_header == ignored_2)
+ continue;
+
+ if (program_header->p_offset > hole_start) {
+ // The hole start is past this segment, so adjust offset.
+ program_header->p_offset += hole_size;
+ VLOG(1) << "phdr[" << i
+ << "] p_offset adjusted to "<< program_header->p_offset;
+ }
+ }
+}
+
+// Helper for ResizeSection(). Find the first loadable segment in the
+// file. We expect it to map from file offset zero.
+ELF::Phdr* FindFirstLoadSegment(ELF::Phdr* program_headers,
+ size_t count) {
+ ELF::Phdr* first_loadable_segment = NULL;
+
+ for (size_t i = 0; i < count; ++i) {
+ ELF::Phdr* program_header = &program_headers[i];
+
+ if (program_header->p_type == PT_LOAD &&
+ program_header->p_offset == 0 &&
+ program_header->p_vaddr == 0 &&
+ program_header->p_paddr == 0) {
+ first_loadable_segment = program_header;
+ }
+ }
+ LOG_IF(FATAL, !first_loadable_segment)
+ << "Cannot locate a LOAD segment with address and offset zero";
+
+ return first_loadable_segment;
+}
+
+// Helper for ResizeSection(). Find the PT_GNU_STACK segment, and check
+// that it contains what we expect so we can restore it on unpack if needed.
+ELF::Phdr* FindUnusedGnuStackSegment(ELF::Phdr* program_headers,
+ size_t count) {
+ ELF::Phdr* unused_segment = NULL;
+
+ for (size_t i = 0; i < count; ++i) {
+ ELF::Phdr* program_header = &program_headers[i];
+
+ if (program_header->p_type == PT_GNU_STACK &&
+ program_header->p_offset == 0 &&
+ program_header->p_vaddr == 0 &&
+ program_header->p_paddr == 0 &&
+ program_header->p_filesz == 0 &&
+ program_header->p_memsz == 0 &&
+ program_header->p_flags == (PF_R | PF_W) &&
+ program_header->p_align == ELF::kGnuStackSegmentAlignment) {
+ unused_segment = program_header;
+ }
+ }
+ LOG_IF(FATAL, !unused_segment)
+ << "Cannot locate the expected GNU_STACK segment";
+
+ return unused_segment;
+}
+
+// Helper for ResizeSection(). Find the segment that was the first loadable
+// one before we split it into two. This is the one into which we coalesce
+// the split segments on unpacking.
+ELF::Phdr* FindOriginalFirstLoadSegment(ELF::Phdr* program_headers,
+ size_t count) {
+ const ELF::Phdr* first_loadable_segment =
+ FindFirstLoadSegment(program_headers, count);
+
+ ELF::Phdr* original_first_loadable_segment = NULL;
+
+ for (size_t i = 0; i < count; ++i) {
+ ELF::Phdr* program_header = &program_headers[i];
+
+ // The original first loadable segment is the one that follows on from
+ // the one we wrote on split to be the current first loadable segment.
+ if (program_header->p_type == PT_LOAD &&
+ program_header->p_offset == first_loadable_segment->p_filesz) {
+ original_first_loadable_segment = program_header;
+ }
+ }
+ LOG_IF(FATAL, !original_first_loadable_segment)
+ << "Cannot locate the LOAD segment that follows a LOAD at offset zero";
+
+ return original_first_loadable_segment;
+}
+
+// Helper for ResizeSection(). Find the segment that contains the hole.
+Elf_Scn* FindSectionContainingHole(Elf* elf,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ Elf_Scn* section = NULL;
+ Elf_Scn* last_unholed_section = NULL;
+
+ while ((section = elf_nextscn(elf, section)) != NULL) {
+ const ELF::Shdr* section_header = ELF::getshdr(section);
+
+ // Because we get here after section headers have been adjusted for the
+ // hole, we need to 'undo' that adjustment to give a view of the original
+ // sections layout.
+ ELF::Off offset = section_header->sh_offset;
+ if (section_header->sh_offset >= hole_start) {
+ offset -= hole_size;
+ }
+
+ if (offset <= hole_start) {
+ last_unholed_section = section;
+ }
+ }
+ LOG_IF(FATAL, !last_unholed_section)
+ << "Cannot identify the section before the one containing the hole";
+
+ // The section containing the hole is the one after the last one found
+ // by the loop above.
+ Elf_Scn* holed_section = elf_nextscn(elf, last_unholed_section);
+ LOG_IF(FATAL, !holed_section)
+ << "Cannot identify the section containing the hole";
+
+ return holed_section;
+}
+
+// Helper for ResizeSection(). Find the last section contained in a segment.
+Elf_Scn* FindLastSectionInSegment(Elf* elf,
+ ELF::Phdr* program_header,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ const ELF::Off segment_end =
+ program_header->p_offset + program_header->p_filesz;
+
+ Elf_Scn* section = NULL;
+ Elf_Scn* last_section = NULL;
+
+ while ((section = elf_nextscn(elf, section)) != NULL) {
+ const ELF::Shdr* section_header = ELF::getshdr(section);
+
+ // As above, 'undo' any section offset adjustment to give a view of the
+ // original sections layout.
+ ELF::Off offset = section_header->sh_offset;
+ if (section_header->sh_offset >= hole_start) {
+ offset -= hole_size;
+ }
+
+ if (offset < segment_end) {
+ last_section = section;
+ }
+ }
+ LOG_IF(FATAL, !last_section)
+ << "Cannot identify the last section in the given segment";
+
+ return last_section;
+}
+
+// Helper for ResizeSection(). Order loadable segments by their offsets.
+// The crazy linker contains assumptions about loadable segment ordering,
+// and it is better if we do not break them.
+void SortOrderSensitiveProgramHeaders(ELF::Phdr* program_headers,
+ size_t count) {
+ std::vector<ELF::Phdr*> orderable;
+
+ // Collect together orderable program headers. These are all the LOAD
+ // segments, and any GNU_STACK that may be present (removed on packing,
+ // but replaced on unpacking).
+ for (size_t i = 0; i < count; ++i) {
+ ELF::Phdr* program_header = &program_headers[i];
+
+ if (program_header->p_type == PT_LOAD ||
+ program_header->p_type == PT_GNU_STACK) {
+ orderable.push_back(program_header);
+ }
+ }
+
+ // Order these program headers so that any PT_GNU_STACK is last, and
+ // the LOAD segments that precede it appear in offset order. Uses
+ // insertion sort.
+ for (size_t i = 1; i < orderable.size(); ++i) {
+ for (size_t j = i; j > 0; --j) {
+ ELF::Phdr* first = orderable[j - 1];
+ ELF::Phdr* second = orderable[j];
+
+ if (!(first->p_type == PT_GNU_STACK ||
+ first->p_offset > second->p_offset)) {
+ break;
+ }
+ std::swap(*first, *second);
+ }
+ }
+}
+
+// Helper for ResizeSection(). The GNU_STACK program header is unused in
+// Android, so we can repurpose it here. Before packing, the program header
+// table contains something like:
+//
+// Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
+// LOAD 0x000000 0x00000000 0x00000000 0x1efc818 0x1efc818 R E 0x1000
+// LOAD 0x1efd008 0x01efe008 0x01efe008 0x17ec3c 0x1a0324 RW 0x1000
+// DYNAMIC 0x205ec50 0x0205fc50 0x0205fc50 0x00108 0x00108 RW 0x4
+// GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0
+//
+// The hole in the file is in the first of these. In order to preserve all
+// load addresses, what we do is to turn the GNU_STACK into a new LOAD entry
+// that maps segments up to where we created the hole, adjust the first LOAD
+// entry so that it maps segments after that, adjust any other program
+// headers whose offset is after the hole start, and finally order the LOAD
+// segments by offset, to give:
+//
+// Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
+// LOAD 0x000000 0x00000000 0x00000000 0x14ea4 0x14ea4 R E 0x1000
+// LOAD 0x014ea4 0x00212ea4 0x00212ea4 0x1cea164 0x1cea164 R E 0x1000
+// DYNAMIC 0x1e60c50 0x0205fc50 0x0205fc50 0x00108 0x00108 RW 0x4
+// LOAD 0x1cff008 0x01efe008 0x01efe008 0x17ec3c 0x1a0324 RW 0x1000
+//
+// We work out the split points by finding the .rel.dyn or .rela.dyn section
+// that contains the hole, and by finding the last section in a given segment.
+//
+// To unpack, we reverse the above to leave the file as it was originally.
+void SplitProgramHeadersForHole(Elf* elf,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ CHECK(hole_size < 0);
+ const ELF::Ehdr* elf_header = ELF::getehdr(elf);
+ CHECK(elf_header);
+
+ ELF::Phdr* elf_program_header = ELF::getphdr(elf);
+ CHECK(elf_program_header);
+
+ const size_t program_header_count = elf_header->e_phnum;
+
+ // Locate the segment that we can overwrite to form the new LOAD entry,
+ // and the segment that we are going to split into two parts.
+ ELF::Phdr* spliced_header =
+ FindUnusedGnuStackSegment(elf_program_header, program_header_count);
+ ELF::Phdr* split_header =
+ FindFirstLoadSegment(elf_program_header, program_header_count);
+
+ VLOG(1) << "phdr[" << split_header - elf_program_header << "] split";
+ VLOG(1) << "phdr[" << spliced_header - elf_program_header << "] new LOAD";
+
+ // Find the section that contains the hole. We split on the section that
+ // follows it.
+ Elf_Scn* holed_section =
+ FindSectionContainingHole(elf, hole_start, hole_size);
+
+ size_t string_index;
+ elf_getshdrstrndx(elf, &string_index);
+
+ ELF::Shdr* section_header = ELF::getshdr(holed_section);
+ std::string name = elf_strptr(elf, string_index, section_header->sh_name);
+ VLOG(1) << "section " << name << " split after";
+
+ // Find the last section in the segment we are splitting.
+ Elf_Scn* last_section =
+ FindLastSectionInSegment(elf, split_header, hole_start, hole_size);
+
+ section_header = ELF::getshdr(last_section);
+ name = elf_strptr(elf, string_index, section_header->sh_name);
+ VLOG(1) << "section " << name << " split end";
+
+ // Split on the section following the holed one, and up to (but not
+ // including) the section following the last one in the split segment.
+ Elf_Scn* split_section = elf_nextscn(elf, holed_section);
+ LOG_IF(FATAL, !split_section)
+ << "No section follows the section that contains the hole";
+ Elf_Scn* end_section = elf_nextscn(elf, last_section);
+ LOG_IF(FATAL, !end_section)
+ << "No section follows the last section in the segment being split";
+
+ // Split the first portion of split_header into spliced_header.
+ const ELF::Shdr* split_section_header = ELF::getshdr(split_section);
+ spliced_header->p_type = split_header->p_type;
+ spliced_header->p_offset = split_header->p_offset;
+ spliced_header->p_vaddr = split_header->p_vaddr;
+ spliced_header->p_paddr = split_header->p_paddr;
+ CHECK(split_header->p_filesz == split_header->p_memsz);
+ spliced_header->p_filesz = split_section_header->sh_offset;
+ spliced_header->p_memsz = split_section_header->sh_offset;
+ spliced_header->p_flags = split_header->p_flags;
+ spliced_header->p_align = split_header->p_align;
+
+ // Now rewrite split_header to remove the part we spliced from it.
+ const ELF::Shdr* end_section_header = ELF::getshdr(end_section);
+ split_header->p_offset = spliced_header->p_filesz;
+ CHECK(split_header->p_vaddr == split_header->p_paddr);
+ split_header->p_vaddr = split_section_header->sh_addr;
+ split_header->p_paddr = split_section_header->sh_addr;
+ CHECK(split_header->p_filesz == split_header->p_memsz);
+ split_header->p_filesz =
+ end_section_header->sh_offset - spliced_header->p_filesz;
+ split_header->p_memsz =
+ end_section_header->sh_offset - spliced_header->p_filesz;
+
+ // Adjust the offsets of all program headers that are not one of the pair
+ // we just created by splitting.
+ AdjustProgramHeaderOffsets(elf_program_header,
+ program_header_count,
+ spliced_header,
+ split_header,
+ hole_start,
+ hole_size);
+
+ // Finally, order loadable segments by offset/address. The crazy linker
+ // contains assumptions about loadable segment ordering.
+ SortOrderSensitiveProgramHeaders(elf_program_header,
+ program_header_count);
+}
+
+// Helper for ResizeSection(). Undo the work of SplitProgramHeadersForHole().
+void CoalesceProgramHeadersForHole(Elf* elf,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ CHECK(hole_size > 0);
+ const ELF::Ehdr* elf_header = ELF::getehdr(elf);
+ CHECK(elf_header);
+
+ ELF::Phdr* elf_program_header = ELF::getphdr(elf);
+ CHECK(elf_program_header);
+
+ const size_t program_header_count = elf_header->e_phnum;
+
+ // Locate the segment that we overwrote to form the new LOAD entry, and
+ // the segment that we split into two parts on packing.
+ ELF::Phdr* spliced_header =
+ FindFirstLoadSegment(elf_program_header, program_header_count);
+ ELF::Phdr* split_header =
+ FindOriginalFirstLoadSegment(elf_program_header, program_header_count);
+
+ VLOG(1) << "phdr[" << spliced_header - elf_program_header << "] stack";
+ VLOG(1) << "phdr[" << split_header - elf_program_header << "] coalesce";
+
+ // Find the last section in the second segment we are coalescing.
+ Elf_Scn* last_section =
+ FindLastSectionInSegment(elf, split_header, hole_start, hole_size);
+
+ size_t string_index;
+ elf_getshdrstrndx(elf, &string_index);
+
+ const ELF::Shdr* section_header = ELF::getshdr(last_section);
+ std::string name = elf_strptr(elf, string_index, section_header->sh_name);
+ VLOG(1) << "section " << name << " coalesced";
+
+ // Rewrite the coalesced segment into split_header.
+ const ELF::Shdr* last_section_header = ELF::getshdr(last_section);
+ split_header->p_offset = spliced_header->p_offset;
+ CHECK(split_header->p_vaddr == split_header->p_paddr);
+ split_header->p_vaddr = spliced_header->p_vaddr;
+ split_header->p_paddr = spliced_header->p_vaddr;
+ CHECK(split_header->p_filesz == split_header->p_memsz);
+ split_header->p_filesz =
+ last_section_header->sh_offset + last_section_header->sh_size;
+ split_header->p_memsz =
+ last_section_header->sh_offset + last_section_header->sh_size;
+
+ // Reconstruct the original GNU_STACK segment into spliced_header.
+ spliced_header->p_type = PT_GNU_STACK;
+ spliced_header->p_offset = 0;
+ spliced_header->p_vaddr = 0;
+ spliced_header->p_paddr = 0;
+ spliced_header->p_filesz = 0;
+ spliced_header->p_memsz = 0;
+ spliced_header->p_flags = PF_R | PF_W;
+ spliced_header->p_align = ELF::kGnuStackSegmentAlignment;
+
+ // Adjust the offsets of all program headers that are not one of the pair
+ // we just coalesced.
+ AdjustProgramHeaderOffsets(elf_program_header,
+ program_header_count,
+ spliced_header,
+ split_header,
+ hole_start,
+ hole_size);
+
+ // Finally, order loadable segments by offset/address. The crazy linker
+ // contains assumptions about loadable segment ordering.
+ SortOrderSensitiveProgramHeaders(elf_program_header,
+ program_header_count);
+}
+
+// Helper for ResizeSection(). Rewrite program headers.
+void RewriteProgramHeadersForHole(Elf* elf,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ // If hole_size is negative then we are removing a piece of the file, and
+ // we want to split program headers so that we keep the same addresses
+ // for text and data. If positive, then we are putting that piece of the
+ // file back in, so we coalesce the previously split program headers.
+ if (hole_size < 0)
+ SplitProgramHeadersForHole(elf, hole_start, hole_size);
+ else if (hole_size > 0)
+ CoalesceProgramHeadersForHole(elf, hole_start, hole_size);
+}
+
+// Helper for ResizeSection(). Locate and return the dynamic section.
+Elf_Scn* GetDynamicSection(Elf* elf) {
+ const ELF::Ehdr* elf_header = ELF::getehdr(elf);
+ CHECK(elf_header);
+
+ const ELF::Phdr* elf_program_header = ELF::getphdr(elf);
+ CHECK(elf_program_header);
+
+ // Find the program header that describes the dynamic section.
+ const ELF::Phdr* dynamic_program_header = NULL;
+ for (size_t i = 0; i < elf_header->e_phnum; ++i) {
+ const ELF::Phdr* program_header = &elf_program_header[i];
+
+ if (program_header->p_type == PT_DYNAMIC) {
+ dynamic_program_header = program_header;
+ }
+ }
+ CHECK(dynamic_program_header);
+
+ // Now find the section with the same offset as this program header.
+ Elf_Scn* dynamic_section = NULL;
+ Elf_Scn* section = NULL;
+ while ((section = elf_nextscn(elf, section)) != NULL) {
+ ELF::Shdr* section_header = ELF::getshdr(section);
+
+ if (section_header->sh_offset == dynamic_program_header->p_offset) {
+ dynamic_section = section;
+ }
+ }
+ CHECK(dynamic_section != NULL);
+
+ return dynamic_section;
+}
+
+// Helper for ResizeSection(). Adjust the .dynamic section for the hole.
+template <typename Rel>
+void AdjustDynamicSectionForHole(Elf_Scn* dynamic_section,
+ ELF::Off hole_start,
+ ssize_t hole_size) {
+ Elf_Data* data = GetSectionData(dynamic_section);
+
+ const ELF::Dyn* dynamic_base = reinterpret_cast<ELF::Dyn*>(data->d_buf);
+ std::vector<ELF::Dyn> dynamics(
+ dynamic_base,
+ dynamic_base + data->d_size / sizeof(dynamics[0]));
+
+ for (size_t i = 0; i < dynamics.size(); ++i) {
+ ELF::Dyn* dynamic = &dynamics[i];
+ const ELF::Sword tag = dynamic->d_tag;
+
+ // DT_RELSZ or DT_RELASZ indicate the overall size of relocations.
+ // Only one will be present. Adjust by hole size.
+ if (tag == DT_RELSZ || tag == DT_RELASZ) {
+ dynamic->d_un.d_val += hole_size;
+ VLOG(1) << "dynamic[" << i << "] " << dynamic->d_tag
+ << " d_val adjusted to " << dynamic->d_un.d_val;
+ }
+
+ // DT_RELCOUNT or DT_RELACOUNT hold the count of relative relocations.
+ // Only one will be present. Packing reduces it to the alignment
+ // padding, if any; unpacking restores it to its former value. The
+ // crazy linker does not use it, but we update it anyway.
+ if (tag == DT_RELCOUNT || tag == DT_RELACOUNT) {
+ // Cast sizeof to a signed type to avoid the division result being
+ // promoted into an unsigned size_t.
+ const ssize_t sizeof_rel = static_cast<ssize_t>(sizeof(Rel));
+ dynamic->d_un.d_val += hole_size / sizeof_rel;
+ VLOG(1) << "dynamic[" << i << "] " << dynamic->d_tag
+ << " d_val adjusted to " << dynamic->d_un.d_val;
+ }
+
+ // DT_RELENT and DT_RELAENT do not change, but make sure they are what
+ // we expect. Only one will be present.
+ if (tag == DT_RELENT || tag == DT_RELAENT) {
+ CHECK(dynamic->d_un.d_val == sizeof(Rel));
+ }
+ }
+
+ void* section_data = &dynamics[0];
+ size_t bytes = dynamics.size() * sizeof(dynamics[0]);
+ RewriteSectionData(dynamic_section, section_data, bytes);
+}
+
+// Resize a section. If the new size is larger than the current size, open
+// up a hole by increasing file offsets that come after the hole. If smaller
+// than the current size, remove the hole by decreasing those offsets.
+template <typename Rel>
+void ResizeSection(Elf* elf, Elf_Scn* section, size_t new_size) {
+ ELF::Shdr* section_header = ELF::getshdr(section);
+ if (section_header->sh_size == new_size)
+ return;
+
+ // Note if we are resizing the real dyn relocations.
+ size_t string_index;
+ elf_getshdrstrndx(elf, &string_index);
+ const std::string section_name =
+ elf_strptr(elf, string_index, section_header->sh_name);
+ const bool is_relocations_resize =
+ (section_name == ".rel.dyn" || section_name == ".rela.dyn");
+
+ // Require that the section size and the data size are the same. True
+ // in practice for all sections we resize when packing or unpacking.
+ Elf_Data* data = GetSectionData(section);
+ CHECK(data->d_off == 0 && data->d_size == section_header->sh_size);
+
+ // Require that the section is not zero-length (that is, has allocated
+ // data that we can validly expand).
+ CHECK(data->d_size && data->d_buf);
+
+ const ELF::Off hole_start = section_header->sh_offset;
+ const ssize_t hole_size = new_size - data->d_size;
+
+ VLOG_IF(1, (hole_size > 0)) << "expand section size = " << data->d_size;
+ VLOG_IF(1, (hole_size < 0)) << "shrink section size = " << data->d_size;
+
+ // Resize the data and the section header.
+ data->d_size += hole_size;
+ section_header->sh_size += hole_size;
+
+ // Add the hole size to all offsets in the ELF file that are after the
+ // start of the hole. If the hole size is positive we are expanding the
+ // section to create a new hole; if negative, we are closing up a hole.
+
+ // Start with the main ELF header.
+ ELF::Ehdr* elf_header = ELF::getehdr(elf);
+ AdjustElfHeaderForHole(elf_header, hole_start, hole_size);
+
+ // Adjust all section headers.
+ AdjustSectionHeadersForHole(elf, hole_start, hole_size);
+
+ // If resizing the dynamic relocations, rewrite the program headers to
+ // either split or coalesce segments, and adjust dynamic entries to match.
+ if (is_relocations_resize) {
+ RewriteProgramHeadersForHole(elf, hole_start, hole_size);
+
+ Elf_Scn* dynamic_section = GetDynamicSection(elf);
+ AdjustDynamicSectionForHole<Rel>(dynamic_section, hole_start, hole_size);
+ }
+}
+
+// Find the first slot in a dynamics array with the given tag. The array
+// always ends with a free (unused) element, and which we exclude from the
+// search. Returns dynamics->size() if not found.
+size_t FindDynamicEntry(ELF::Sword tag,
+ std::vector<ELF::Dyn>* dynamics) {
+ // Loop until the penultimate entry. We exclude the end sentinel.
+ for (size_t i = 0; i < dynamics->size() - 1; ++i) {
+ if (dynamics->at(i).d_tag == tag)
+ return i;
+ }
+
+ // The tag was not found.
+ return dynamics->size();
+}
+
+// Replace the first free (unused) slot in a dynamics vector with the given
+// value. The vector always ends with a free (unused) element, so the slot
+// found cannot be the last one in the vector.
+void AddDynamicEntry(const ELF::Dyn& dyn,
+ std::vector<ELF::Dyn>* dynamics) {
+ const size_t slot = FindDynamicEntry(DT_NULL, dynamics);
+ if (slot == dynamics->size()) {
+ LOG(FATAL) << "No spare dynamic array slots found "
+ << "(to fix, increase gold's --spare-dynamic-tags value)";
+ }
+
+ // Replace this entry with the one supplied.
+ dynamics->at(slot) = dyn;
+ VLOG(1) << "dynamic[" << slot << "] overwritten with " << dyn.d_tag;
+}
+
+// Remove the element in the dynamics vector that matches the given tag with
+// unused slot data. Shuffle the following elements up, and ensure that the
+// last is the null sentinel.
+void RemoveDynamicEntry(ELF::Sword tag,
+ std::vector<ELF::Dyn>* dynamics) {
+ const size_t slot = FindDynamicEntry(tag, dynamics);
+ CHECK(slot != dynamics->size());
+
+ // Remove this entry by shuffling up everything that follows.
+ for (size_t i = slot; i < dynamics->size() - 1; ++i) {
+ dynamics->at(i) = dynamics->at(i + 1);
+ VLOG(1) << "dynamic[" << i
+ << "] overwritten with dynamic[" << i + 1 << "]";
+ }
+
+ // Ensure that the end sentinel is still present.
+ CHECK(dynamics->at(dynamics->size() - 1).d_tag == DT_NULL);
+}
+
+// Construct a null relocation without addend.
+void NullRelocation(ELF::Rel* relocation) {
+ relocation->r_offset = 0;
+ relocation->r_info = ELF_R_INFO(0, ELF::kNoRelocationCode);
+}
+
+// Construct a null relocation with addend.
+void NullRelocation(ELF::Rela* relocation) {
+ relocation->r_offset = 0;
+ relocation->r_info = ELF_R_INFO(0, ELF::kNoRelocationCode);
+ relocation->r_addend = 0;
+}
+
+// Pad relocations with the given number of null entries. Generates its
+// null entry with the appropriate NullRelocation() invocation.
+template <typename Rel>
+void PadRelocations(size_t count, std::vector<Rel>* relocations) {
+ Rel null_relocation;
+ NullRelocation(&null_relocation);
+ std::vector<Rel> padding(count, null_relocation);
+ relocations->insert(relocations->end(), padding.begin(), padding.end());
+}
+
+} // namespace
+
+// Remove relative entries from dynamic relocations and write as packed
+// data into android packed relocations.
+bool ElfFile::PackRelocations() {
+ // Load the ELF file into libelf.
+ if (!Load()) {
+ LOG(ERROR) << "Failed to load as ELF";
+ return false;
+ }
+
+ // Retrieve the current dynamic relocations section data.
+ Elf_Data* data = GetSectionData(relocations_section_);
+
+ if (relocations_type_ == REL) {
+ // Convert data to a vector of relocations.
+ const ELF::Rel* relocations_base = reinterpret_cast<ELF::Rel*>(data->d_buf);
+ std::vector<ELF::Rel> relocations(
+ relocations_base,
+ relocations_base + data->d_size / sizeof(relocations[0]));
+
+ LOG(INFO) << "Relocations : REL";
+ return PackTypedRelocations<ELF::Rel>(relocations);
+ }
+
+ if (relocations_type_ == RELA) {
+ // Convert data to a vector of relocations with addends.
+ const ELF::Rela* relocations_base =
+ reinterpret_cast<ELF::Rela*>(data->d_buf);
+ std::vector<ELF::Rela> relocations(
+ relocations_base,
+ relocations_base + data->d_size / sizeof(relocations[0]));
+
+ LOG(INFO) << "Relocations : RELA";
+ return PackTypedRelocations<ELF::Rela>(relocations);
+ }
+
+ NOTREACHED();
+ return false;
+}
+
+// Helper for PackRelocations(). Rel type is one of ELF::Rel or ELF::Rela.
+template <typename Rel>
+bool ElfFile::PackTypedRelocations(const std::vector<Rel>& relocations) {
+ // Filter relocations into those that are relative and others.
+ std::vector<Rel> relative_relocations;
+ std::vector<Rel> other_relocations;
+
+ for (size_t i = 0; i < relocations.size(); ++i) {
+ const Rel& relocation = relocations[i];
+ if (ELF_R_TYPE(relocation.r_info) == ELF::kRelativeRelocationCode) {
+ CHECK(ELF_R_SYM(relocation.r_info) == 0);
+ relative_relocations.push_back(relocation);
+ } else {
+ other_relocations.push_back(relocation);
+ }
+ }
+ LOG(INFO) << "Relative : " << relative_relocations.size() << " entries";
+ LOG(INFO) << "Other : " << other_relocations.size() << " entries";
+ LOG(INFO) << "Total : " << relocations.size() << " entries";
+
+ // If no relative relocations then we have nothing packable. Perhaps
+ // the shared object has already been packed?
+ if (relative_relocations.empty()) {
+ LOG(ERROR) << "No relative relocations found (already packed?)";
+ return false;
+ }
+
+ // If not padding fully, apply only enough padding to preserve alignment.
+ // Otherwise, pad so that we do not shrink the relocations section at all.
+ if (!is_padding_relocations_) {
+ // Calculate the size of the hole we will close up when we rewrite
+ // dynamic relocations.
+ ssize_t hole_size =
+ relative_relocations.size() * sizeof(relative_relocations[0]);
+ const ssize_t unaligned_hole_size = hole_size;
+
+ // Adjust the actual hole size to preserve alignment. We always adjust
+ // by a whole number of NONE-type relocations.
+ while (hole_size % kPreserveAlignment)
+ hole_size -= sizeof(relative_relocations[0]);
+ LOG(INFO) << "Compaction : " << hole_size << " bytes";
+
+ // Adjusting for alignment may have removed any packing benefit.
+ if (hole_size == 0) {
+ LOG(INFO) << "Too few relative relocations to pack after alignment";
+ return false;
+ }
+
+ // Find the padding needed in other_relocations to preserve alignment.
+ // Ensure that we never completely empty the real relocations section.
+ size_t padding_bytes = unaligned_hole_size - hole_size;
+ if (padding_bytes == 0 && other_relocations.size() == 0) {
+ do {
+ padding_bytes += sizeof(relative_relocations[0]);
+ } while (padding_bytes % kPreserveAlignment);
+ }
+ CHECK(padding_bytes % sizeof(other_relocations[0]) == 0);
+ const size_t padding = padding_bytes / sizeof(other_relocations[0]);
+
+ // Padding may have removed any packing benefit.
+ if (padding >= relative_relocations.size()) {
+ LOG(INFO) << "Too few relative relocations to pack after padding";
+ return false;
+ }
+
+ // Add null relocations to other_relocations to preserve alignment.
+ PadRelocations<Rel>(padding, &other_relocations);
+ LOG(INFO) << "Alignment pad : " << padding << " relocations";
+ } else {
+ // If padding, add NONE-type relocations to other_relocations to make it
+ // the same size as the the original relocations we read in. This makes
+ // the ResizeSection() below a no-op.
+ const size_t padding = relocations.size() - other_relocations.size();
+ PadRelocations<Rel>(padding, &other_relocations);
+ }
+
+ // Pack relative relocations.
+ const size_t initial_bytes =
+ relative_relocations.size() * sizeof(relative_relocations[0]);
+ LOG(INFO) << "Unpacked relative: " << initial_bytes << " bytes";
+ std::vector<uint8_t> packed;
+ RelocationPacker packer;
+ packer.PackRelativeRelocations(relative_relocations, &packed);
+ const void* packed_data = &packed[0];
+ const size_t packed_bytes = packed.size() * sizeof(packed[0]);
+ LOG(INFO) << "Packed relative: " << packed_bytes << " bytes";
+
+ // If we have insufficient relative relocations to form a run then
+ // packing fails.
+ if (packed.empty()) {
+ LOG(INFO) << "Too few relative relocations to pack";
+ return false;
+ }
+
+ // Run a loopback self-test as a check that packing is lossless.
+ std::vector<Rel> unpacked;
+ packer.UnpackRelativeRelocations(packed, &unpacked);
+ CHECK(unpacked.size() == relative_relocations.size());
+ CHECK(!memcmp(&unpacked[0],
+ &relative_relocations[0],
+ unpacked.size() * sizeof(unpacked[0])));
+
+ // Make sure packing saved some space.
+ if (packed_bytes >= initial_bytes) {
+ LOG(INFO) << "Packing relative relocations saves no space";
+ return false;
+ }
+
+ // Rewrite the current dynamic relocations section to be only the ARM
+ // non-relative relocations, then shrink it to size.
+ const void* section_data = &other_relocations[0];
+ const size_t bytes = other_relocations.size() * sizeof(other_relocations[0]);
+ ResizeSection<Rel>(elf_, relocations_section_, bytes);
+ RewriteSectionData(relocations_section_, section_data, bytes);
+
+ // Rewrite the current packed android relocations section to hold the packed
+ // relative relocations.
+ ResizeSection<Rel>(elf_, android_relocations_section_, packed_bytes);
+ RewriteSectionData(android_relocations_section_, packed_data, packed_bytes);
+
+ // Rewrite .dynamic to include two new tags describing the packed android
+ // relocations.
+ Elf_Data* data = GetSectionData(dynamic_section_);
+ const ELF::Dyn* dynamic_base = reinterpret_cast<ELF::Dyn*>(data->d_buf);
+ std::vector<ELF::Dyn> dynamics(
+ dynamic_base,
+ dynamic_base + data->d_size / sizeof(dynamics[0]));
+ // Use two of the spare slots to describe the packed section.
+ ELF::Shdr* section_header = ELF::getshdr(android_relocations_section_);
+ {
+ ELF::Dyn dyn;
+ dyn.d_tag = DT_ANDROID_REL_OFFSET;
+ dyn.d_un.d_ptr = section_header->sh_offset;
+ AddDynamicEntry(dyn, &dynamics);
+ }
+ {
+ ELF::Dyn dyn;
+ dyn.d_tag = DT_ANDROID_REL_SIZE;
+ dyn.d_un.d_val = section_header->sh_size;
+ AddDynamicEntry(dyn, &dynamics);
+ }
+ const void* dynamics_data = &dynamics[0];
+ const size_t dynamics_bytes = dynamics.size() * sizeof(dynamics[0]);
+ RewriteSectionData(dynamic_section_, dynamics_data, dynamics_bytes);
+
+ Flush();
+ return true;
+}
+
+// Find packed relative relocations in the packed android relocations
+// section, unpack them, and rewrite the dynamic relocations section to
+// contain unpacked data.
+bool ElfFile::UnpackRelocations() {
+ // Load the ELF file into libelf.
+ if (!Load()) {
+ LOG(ERROR) << "Failed to load as ELF";
+ return false;
+ }
+
+ // Retrieve the current packed android relocations section data.
+ Elf_Data* data = GetSectionData(android_relocations_section_);
+
+ // Convert data to a vector of bytes.
+ const uint8_t* packed_base = reinterpret_cast<uint8_t*>(data->d_buf);
+ std::vector<uint8_t> packed(
+ packed_base,
+ packed_base + data->d_size / sizeof(packed[0]));
+
+ if (packed.size() > 3 &&
+ packed[0] == 'A' &&
+ packed[1] == 'P' &&
+ packed[2] == 'R' &&
+ packed[3] == '1') {
+ // Signature is APR1, unpack relocations.
+ CHECK(relocations_type_ == REL);
+ LOG(INFO) << "Relocations : REL";
+ return UnpackTypedRelocations<ELF::Rel>(packed);
+ }
+
+ if (packed.size() > 3 &&
+ packed[0] == 'A' &&
+ packed[1] == 'P' &&
+ packed[2] == 'A' &&
+ packed[3] == '1') {
+ // Signature is APA1, unpack relocations with addends.
+ CHECK(relocations_type_ == RELA);
+ LOG(INFO) << "Relocations : RELA";
+ return UnpackTypedRelocations<ELF::Rela>(packed);
+ }
+
+ LOG(ERROR) << "Packed relative relocations not found (not packed?)";
+ return false;
+}
+
+// Helper for UnpackRelocations(). Rel type is one of ELF::Rel or ELF::Rela.
+template <typename Rel>
+bool ElfFile::UnpackTypedRelocations(const std::vector<uint8_t>& packed) {
+ // Unpack the data to re-materialize the relative relocations.
+ const size_t packed_bytes = packed.size() * sizeof(packed[0]);
+ LOG(INFO) << "Packed relative: " << packed_bytes << " bytes";
+ std::vector<Rel> relative_relocations;
+ RelocationPacker packer;
+ packer.UnpackRelativeRelocations(packed, &relative_relocations);
+ const size_t unpacked_bytes =
+ relative_relocations.size() * sizeof(relative_relocations[0]);
+ LOG(INFO) << "Unpacked relative: " << unpacked_bytes << " bytes";
+
+ // Retrieve the current dynamic relocations section data.
+ Elf_Data* data = GetSectionData(relocations_section_);
+
+ // Interpret data as relocations.
+ const Rel* relocations_base = reinterpret_cast<Rel*>(data->d_buf);
+ std::vector<Rel> relocations(
+ relocations_base,
+ relocations_base + data->d_size / sizeof(relocations[0]));
+
+ std::vector<Rel> other_relocations;
+ size_t padding = 0;
+
+ // Filter relocations to locate any that are NONE-type. These will occur
+ // if padding was turned on for packing.
+ for (size_t i = 0; i < relocations.size(); ++i) {
+ const Rel& relocation = relocations[i];
+ if (ELF_R_TYPE(relocation.r_info) != ELF::kNoRelocationCode) {
+ other_relocations.push_back(relocation);
+ } else {
+ ++padding;
+ }
+ }
+ LOG(INFO) << "Relative : " << relative_relocations.size() << " entries";
+ LOG(INFO) << "Other : " << other_relocations.size() << " entries";
+
+ // If we found the same number of null relocation entries in the dynamic
+ // relocations section as we hold as unpacked relative relocations, then
+ // this is a padded file.
+ const bool is_padded = padding == relative_relocations.size();
+
+ // Unless padded, report by how much we expand the file.
+ if (!is_padded) {
+ // Calculate the size of the hole we will open up when we rewrite
+ // dynamic relocations.
+ ssize_t hole_size =
+ relative_relocations.size() * sizeof(relative_relocations[0]);
+
+ // Adjust the hole size for the padding added to preserve alignment.
+ hole_size -= padding * sizeof(other_relocations[0]);
+ LOG(INFO) << "Expansion : " << hole_size << " bytes";
+ }
+
+ // Rewrite the current dynamic relocations section to be the relative
+ // relocations followed by other relocations. This is the usual order in
+ // which we find them after linking, so this action will normally put the
+ // entire dynamic relocations section back to its pre-split-and-packed state.
+ relocations.assign(relative_relocations.begin(), relative_relocations.end());
+ relocations.insert(relocations.end(),
+ other_relocations.begin(), other_relocations.end());
+ const void* section_data = &relocations[0];
+ const size_t bytes = relocations.size() * sizeof(relocations[0]);
+ LOG(INFO) << "Total : " << relocations.size() << " entries";
+ ResizeSection<Rel>(elf_, relocations_section_, bytes);
+ RewriteSectionData(relocations_section_, section_data, bytes);
+
+ // Nearly empty the current packed android relocations section. Leaves a
+ // four-byte stub so that some data remains allocated to the section.
+ // This is a convenience which allows us to re-pack this file again without
+ // having to remove the section and then add a new small one with objcopy.
+ // The way we resize sections relies on there being some data in a section.
+ ResizeSection<Rel>(
+ elf_, android_relocations_section_, sizeof(kStubIdentifier));
+ RewriteSectionData(
+ android_relocations_section_, &kStubIdentifier, sizeof(kStubIdentifier));
+
+ // Rewrite .dynamic to remove two tags describing packed android relocations.
+ data = GetSectionData(dynamic_section_);
+ const ELF::Dyn* dynamic_base = reinterpret_cast<ELF::Dyn*>(data->d_buf);
+ std::vector<ELF::Dyn> dynamics(
+ dynamic_base,
+ dynamic_base + data->d_size / sizeof(dynamics[0]));
+ RemoveDynamicEntry(DT_ANDROID_REL_OFFSET, &dynamics);
+ RemoveDynamicEntry(DT_ANDROID_REL_SIZE, &dynamics);
+ const void* dynamics_data = &dynamics[0];
+ const size_t dynamics_bytes = dynamics.size() * sizeof(dynamics[0]);
+ RewriteSectionData(dynamic_section_, dynamics_data, dynamics_bytes);
+
+ Flush();
+ return true;
+}
+
+// Flush rewritten shared object file data.
+void ElfFile::Flush() {
+ // Flag all ELF data held in memory as needing to be written back to the
+ // file, and tell libelf that we have controlled the file layout.
+ elf_flagelf(elf_, ELF_C_SET, ELF_F_DIRTY);
+ elf_flagelf(elf_, ELF_C_SET, ELF_F_LAYOUT);
+
+ // Write ELF data back to disk.
+ const off_t file_bytes = elf_update(elf_, ELF_C_WRITE);
+ CHECK(file_bytes > 0);
+ VLOG(1) << "elf_update returned: " << file_bytes;
+
+ // Clean up libelf, and truncate the output file to the number of bytes
+ // written by elf_update().
+ elf_end(elf_);
+ elf_ = NULL;
+ const int truncate = ftruncate(fd_, file_bytes);
+ CHECK(truncate == 0);
+}
+
+} // namespace relocation_packer