| // 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. |
| |
| // TODO(simonb): Extend for 64-bit target libraries. |
| |
| #include "elf_file.h" |
| |
| #include <stdlib.h> |
| #include <sys/types.h> |
| #include <unistd.h> |
| #include <string> |
| #include <vector> |
| |
| #include "debug.h" |
| #include "libelf.h" |
| #include "packer.h" |
| |
| namespace relocation_packer { |
| |
| // Stub identifier written to 'null out' packed data, "NULL". |
| static const Elf32_Word kStubIdentifier = 0x4c4c554eu; |
| |
| // Out-of-band dynamic tags used to indicate the offset and size of the |
| // .android.rel.dyn section. |
| static const Elf32_Sword DT_ANDROID_ARM_REL_OFFSET = DT_LOPROC; |
| static const Elf32_Sword DT_ANDROID_ARM_REL_SIZE = DT_LOPROC + 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. |
| static const size_t kPreserveAlignment = 256; |
| |
| 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_Data* data, |
| const void* section_data, |
| size_t size) { |
| 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 Elf32_Ehdr* elf_header) { |
| VLOG("e_phoff = %u\n", elf_header->e_phoff); |
| VLOG("e_shoff = %u\n", elf_header->e_shoff); |
| VLOG("e_ehsize = %u\n", elf_header->e_ehsize); |
| VLOG("e_phentsize = %u\n", elf_header->e_phentsize); |
| VLOG("e_phnum = %u\n", elf_header->e_phnum); |
| VLOG("e_shnum = %u\n", elf_header->e_shnum); |
| VLOG("e_shstrndx = %u\n", elf_header->e_shstrndx); |
| } |
| |
| // Verbose ELF program header logging. |
| void VerboseLogProgramHeader(size_t program_header_index, |
| const Elf32_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_NOTE: type = "NOTE"; break; |
| case PT_SHLIB: type = "SHLIB"; break; |
| case PT_PHDR: type = "PHDR"; break; |
| case PT_TLS: type = "TLS"; break; |
| default: type = "(OTHER)"; break; |
| } |
| VLOG("phdr %lu : %s\n", program_header_index, type.c_str()); |
| VLOG(" p_offset = %u\n", program_header->p_offset); |
| VLOG(" p_vaddr = %u\n", program_header->p_vaddr); |
| VLOG(" p_paddr = %u\n", program_header->p_paddr); |
| VLOG(" p_filesz = %u\n", program_header->p_filesz); |
| VLOG(" p_memsz = %u\n", program_header->p_memsz); |
| } |
| |
| // Verbose ELF section header logging. |
| void VerboseLogSectionHeader(const std::string& section_name, |
| const Elf32_Shdr* section_header) { |
| VLOG("section %s\n", section_name.c_str()); |
| VLOG(" sh_addr = %u\n", section_header->sh_addr); |
| VLOG(" sh_offset = %u\n", section_header->sh_offset); |
| VLOG(" sh_size = %u\n", section_header->sh_size); |
| VLOG(" sh_addralign = %u\n", section_header->sh_addralign); |
| } |
| |
| // Verbose ELF section data logging. |
| void VerboseLogSectionData(const Elf_Data* data) { |
| VLOG(" data\n"); |
| VLOG(" d_buf = %p\n", data->d_buf); |
| VLOG(" d_off = %lu\n", data->d_off); |
| VLOG(" d_size = %lu\n", data->d_size); |
| VLOG(" d_align = %lu\n", data->d_align); |
| } |
| |
| } // namespace |
| |
| // Load the complete ELF file into a memory image in libelf, and identify |
| // the .rel.dyn, .dynamic, and .android.rel.dyn sections. No-op if the |
| // ELF file has already been loaded. |
| bool ElfFile::Load() { |
| if (elf_) |
| return true; |
| |
| elf_ = elf_begin(fd_, ELF_C_RDWR, NULL); |
| CHECK(elf_); |
| |
| if (elf_kind(elf_) != ELF_K_ELF) { |
| LOG("ERROR: File not in ELF format\n"); |
| return false; |
| } |
| |
| Elf32_Ehdr* elf_header = elf32_getehdr(elf_); |
| if (!elf_header) { |
| LOG("ERROR: Failed to load ELF header\n"); |
| return false; |
| } |
| if (elf_header->e_machine != EM_ARM) { |
| LOG("ERROR: File is not an arm32 ELF file\n"); |
| 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 = static_cast<int>(elf_header->e_ident[5]); |
| CHECK(endian == ELFDATA2LSB); |
| CHECK(__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__); |
| |
| VLOG("endian = %u\n", endian); |
| VerboseLogElfHeader(elf_header); |
| |
| const Elf32_Phdr* elf_program_header = elf32_getphdr(elf_); |
| CHECK(elf_program_header); |
| |
| const Elf32_Phdr* dynamic_program_header = NULL; |
| for (size_t i = 0; i < elf_header->e_phnum; ++i) { |
| const Elf32_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 .rel.dyn, .android.rel.dyn, and .dynamic sections. Found |
| // while iterating sections, and later stored in class attributes. |
| Elf_Scn* found_rel_dyn_section = NULL; |
| Elf_Scn* found_android_rel_dyn_section = NULL; |
| Elf_Scn* found_dynamic_section = NULL; |
| |
| // Flag set if we encounter any .debug* section. We do not adjust any |
| // offsets or addresses of any debug data, so if we find one of these then |
| // the resulting output shared object should still run, but might not be |
| // usable for debugging, disassembly, and so on. Provides a warning if |
| // this occurs. |
| bool has_debug_section = false; |
| |
| Elf_Scn* section = NULL; |
| while ((section = elf_nextscn(elf_, section)) != NULL) { |
| const Elf32_Shdr* section_header = elf32_getshdr(section); |
| std::string name = elf_strptr(elf_, string_index, section_header->sh_name); |
| VerboseLogSectionHeader(name, section_header); |
| |
| // Note special sections as we encounter them. |
| if (name == ".rel.dyn") { |
| found_rel_dyn_section = section; |
| } |
| if (name == ".android.rel.dyn") { |
| found_android_rel_dyn_section = section; |
| } |
| if (section_header->sh_offset == dynamic_program_header->p_offset) { |
| found_dynamic_section = section; |
| } |
| |
| // If we find a section named .debug*, set the debug warning flag. |
| if (std::string(name).find(".debug") == 0) { |
| has_debug_section = true; |
| } |
| |
| // 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_rel_dyn_section) { |
| LOG("ERROR: Missing .rel.dyn section\n"); |
| return false; |
| } |
| if (!found_dynamic_section) { |
| LOG("ERROR: Missing .dynamic section\n"); |
| return false; |
| } |
| if (!found_android_rel_dyn_section) { |
| LOG("ERROR: Missing .android.rel.dyn section " |
| "(to fix, run with --help and follow the pre-packing instructions)\n"); |
| return false; |
| } |
| |
| if (has_debug_section) { |
| LOG("WARNING: found .debug section(s), and ignored them\n"); |
| } |
| |
| rel_dyn_section_ = found_rel_dyn_section; |
| dynamic_section_ = found_dynamic_section; |
| android_rel_dyn_section_ = found_android_rel_dyn_section; |
| return true; |
| } |
| |
| namespace { |
| |
| // Helper for ResizeSection(). Adjust the main ELF header for the hole. |
| void AdjustElfHeaderForHole(Elf32_Ehdr* elf_header, |
| Elf32_Off hole_start, |
| int32_t hole_size) { |
| if (elf_header->e_phoff > hole_start) { |
| elf_header->e_phoff += hole_size; |
| VLOG("e_phoff adjusted to %u\n", elf_header->e_phoff); |
| } |
| if (elf_header->e_shoff > hole_start) { |
| elf_header->e_shoff += hole_size; |
| VLOG("e_shoff adjusted to %u\n", elf_header->e_shoff); |
| } |
| } |
| |
| // Helper for ResizeSection(). Adjust all program headers for the hole. |
| void AdjustProgramHeadersForHole(Elf32_Phdr* elf_program_header, |
| size_t program_header_count, |
| Elf32_Off hole_start, |
| int32_t hole_size) { |
| for (size_t i = 0; i < program_header_count; ++i) { |
| Elf32_Phdr* program_header = &elf_program_header[i]; |
| |
| if (program_header->p_offset > hole_start) { |
| // The hole start is past this segment, so adjust offsets and addrs. |
| program_header->p_offset += hole_size; |
| VLOG("phdr %lu p_offset adjusted to %u\n", i, program_header->p_offset); |
| |
| // Only adjust vaddr and paddr if this program header has them. |
| if (program_header->p_vaddr != 0) { |
| program_header->p_vaddr += hole_size; |
| VLOG("phdr %lu p_vaddr adjusted to %u\n", i, program_header->p_vaddr); |
| } |
| if (program_header->p_paddr != 0) { |
| program_header->p_paddr += hole_size; |
| VLOG("phdr %lu p_paddr adjusted to %u\n", i, program_header->p_paddr); |
| } |
| } else if (program_header->p_offset + |
| program_header->p_filesz > hole_start) { |
| // The hole start is within this segment, so adjust file and in-memory |
| // sizes, but leave offsets and addrs unchanged. |
| program_header->p_filesz += hole_size; |
| VLOG("phdr %lu p_filesz adjusted to %u\n", i, program_header->p_filesz); |
| program_header->p_memsz += hole_size; |
| VLOG("phdr %lu p_memsz adjusted to %u\n", i, program_header->p_memsz); |
| } |
| } |
| } |
| |
| // Helper for ResizeSection(). Adjust all section headers for the hole. |
| void AdjustSectionHeadersForHole(Elf* elf, |
| Elf32_Off hole_start, |
| int32_t hole_size) { |
| size_t string_index; |
| elf_getshdrstrndx(elf, &string_index); |
| |
| Elf_Scn* section = NULL; |
| while ((section = elf_nextscn(elf, section)) != NULL) { |
| Elf32_Shdr* section_header = elf32_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("section %s sh_offset" |
| " adjusted to %u\n", name.c_str(), section_header->sh_offset); |
| // Only adjust section addr if this section has one. |
| if (section_header->sh_addr != 0) { |
| section_header->sh_addr += hole_size; |
| VLOG("section %s sh_addr" |
| " adjusted to %u\n", name.c_str(), section_header->sh_addr); |
| } |
| } |
| } |
| } |
| |
| // Helper for ResizeSection(). Adjust the .dynamic section for the hole. |
| void AdjustDynamicSectionForHole(Elf_Scn* dynamic_section, |
| bool is_rel_dyn_resize, |
| Elf32_Off hole_start, |
| int32_t hole_size) { |
| Elf_Data* data = GetSectionData(dynamic_section); |
| |
| const Elf32_Dyn* dynamic_base = reinterpret_cast<Elf32_Dyn*>(data->d_buf); |
| std::vector<Elf32_Dyn> dynamics( |
| dynamic_base, |
| dynamic_base + data->d_size / sizeof(dynamics[0])); |
| |
| for (size_t i = 0; i < dynamics.size(); ++i) { |
| Elf32_Dyn* dynamic = &dynamics[i]; |
| const Elf32_Sword tag = dynamic->d_tag; |
| // Any tags that hold offsets are adjustment candidates. |
| const bool is_adjustable = (tag == DT_PLTGOT || |
| tag == DT_HASH || |
| tag == DT_STRTAB || |
| tag == DT_SYMTAB || |
| tag == DT_RELA || |
| tag == DT_INIT || |
| tag == DT_FINI || |
| tag == DT_REL || |
| tag == DT_JMPREL || |
| tag == DT_INIT_ARRAY || |
| tag == DT_FINI_ARRAY || |
| tag == DT_ANDROID_ARM_REL_OFFSET); |
| if (is_adjustable && dynamic->d_un.d_ptr > hole_start) { |
| dynamic->d_un.d_ptr += hole_size; |
| VLOG("dynamic[%lu] %u" |
| " d_ptr adjusted to %u\n", i, dynamic->d_tag, dynamic->d_un.d_ptr); |
| } |
| |
| // If we are specifically resizing .rel.dyn, we need to make some added |
| // adjustments to tags that indicate the counts of R_ARM_RELATIVE |
| // relocations in the shared object. |
| if (is_rel_dyn_resize) { |
| // DT_RELSZ is the overall size of relocations. Adjust by hole size. |
| if (tag == DT_RELSZ) { |
| dynamic->d_un.d_val += hole_size; |
| VLOG("dynamic[%lu] %u" |
| " d_val adjusted to %u\n", i, dynamic->d_tag, dynamic->d_un.d_val); |
| } |
| |
| // The crazy linker does not use DT_RELCOUNT, but we keep it updated |
| // anyway. In practice the section hole is always equal to the size |
| // of R_ARM_RELATIVE relocations, and DT_RELCOUNT is the count of |
| // relative relocations. So closing a hole on packing reduces |
| // DT_RELCOUNT to zero, and opening a hole on unpacking restores it to |
| // its pre-packed value. |
| if (tag == DT_RELCOUNT) { |
| dynamic->d_un.d_val += hole_size / sizeof(Elf32_Rel); |
| VLOG("dynamic[%lu] %u" |
| " d_val adjusted to %u\n", i, dynamic->d_tag, dynamic->d_un.d_val); |
| } |
| |
| // DT_RELENT doesn't change, but make sure it is what we expect. |
| if (tag == DT_RELENT) { |
| CHECK(dynamic->d_un.d_val == sizeof(Elf32_Rel)); |
| } |
| } |
| } |
| |
| void* section_data = &dynamics[0]; |
| size_t bytes = dynamics.size() * sizeof(dynamics[0]); |
| RewriteSectionData(data, section_data, bytes); |
| } |
| |
| // Helper for ResizeSection(). Adjust the .dynsym section for the hole. |
| // We need to adjust the values for the symbols represented in it. |
| void AdjustDynSymSectionForHole(Elf_Scn* dynsym_section, |
| Elf32_Off hole_start, |
| int32_t hole_size) { |
| Elf_Data* data = GetSectionData(dynsym_section); |
| |
| const Elf32_Sym* dynsym_base = reinterpret_cast<Elf32_Sym*>(data->d_buf); |
| std::vector<Elf32_Sym> dynsyms |
| (dynsym_base, |
| dynsym_base + data->d_size / sizeof(dynsyms[0])); |
| |
| for (size_t i = 0; i < dynsyms.size(); ++i) { |
| Elf32_Sym* dynsym = &dynsyms[i]; |
| const int type = static_cast<int>(ELF32_ST_TYPE(dynsym->st_info)); |
| const bool is_adjustable = (type == STT_OBJECT || |
| type == STT_FUNC || |
| type == STT_SECTION || |
| type == STT_FILE || |
| type == STT_COMMON || |
| type == STT_TLS); |
| if (is_adjustable && dynsym->st_value > hole_start) { |
| dynsym->st_value += hole_size; |
| VLOG("dynsym[%lu] type=%u" |
| " st_value adjusted to %u\n", i, type, dynsym->st_value); |
| } |
| } |
| |
| void* section_data = &dynsyms[0]; |
| size_t bytes = dynsyms.size() * sizeof(dynsyms[0]); |
| RewriteSectionData(data, section_data, bytes); |
| } |
| |
| // Helper for ResizeSection(). Adjust the .rel.plt section for the hole. |
| // We need to adjust the offset of every relocation inside it that falls |
| // beyond the hole start. |
| void AdjustRelPltSectionForHole(Elf_Scn* relplt_section, |
| Elf32_Off hole_start, |
| int32_t hole_size) { |
| Elf_Data* data = GetSectionData(relplt_section); |
| |
| const Elf32_Rel* relplt_base = reinterpret_cast<Elf32_Rel*>(data->d_buf); |
| std::vector<Elf32_Rel> relplts( |
| relplt_base, |
| relplt_base + data->d_size / sizeof(relplts[0])); |
| |
| for (size_t i = 0; i < relplts.size(); ++i) { |
| Elf32_Rel* relplt = &relplts[i]; |
| if (relplt->r_offset > hole_start) { |
| relplt->r_offset += hole_size; |
| VLOG("relplt[%lu] r_offset adjusted to %u\n", i, relplt->r_offset); |
| } |
| } |
| |
| void* section_data = &relplts[0]; |
| size_t bytes = relplts.size() * sizeof(relplts[0]); |
| RewriteSectionData(data, section_data, bytes); |
| } |
| |
| // Helper for ResizeSection(). Adjust the .symtab section for the hole. |
| // We want to adjust the value of every symbol in it that falls beyond |
| // the hole start. |
| void AdjustSymTabSectionForHole(Elf_Scn* symtab_section, |
| Elf32_Off hole_start, |
| int32_t hole_size) { |
| Elf_Data* data = GetSectionData(symtab_section); |
| |
| const Elf32_Sym* symtab_base = reinterpret_cast<Elf32_Sym*>(data->d_buf); |
| std::vector<Elf32_Sym> symtab( |
| symtab_base, |
| symtab_base + data->d_size / sizeof(symtab[0])); |
| |
| for (size_t i = 0; i < symtab.size(); ++i) { |
| Elf32_Sym* sym = &symtab[i]; |
| if (sym->st_value > hole_start) { |
| sym->st_value += hole_size; |
| VLOG("symtab[%lu] value adjusted to %u\n", i, sym->st_value); |
| } |
| } |
| |
| void* section_data = &symtab[0]; |
| size_t bytes = symtab.size() * sizeof(symtab[0]); |
| RewriteSectionData(data, 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. |
| void ResizeSection(Elf* elf, Elf_Scn* section, size_t new_size) { |
| Elf32_Shdr* section_header = elf32_getshdr(section); |
| if (section_header->sh_size == new_size) |
| return; |
| |
| // Note if we are resizing the real .rel.dyn. If yes, then we have to |
| // massage d_un.d_val in the dynamic section where d_tag is DT_RELSZ and |
| // DT_RELCOUNT. |
| 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_rel_dyn_resize = section_name == ".rel.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 Elf32_Off hole_start = section_header->sh_offset; |
| const int32_t hole_size = new_size - data->d_size; |
| |
| VLOG_IF(hole_size > 0, "expand section size = %lu\n", data->d_size); |
| VLOG_IF(hole_size < 0, "shrink section size = %lu\n", data->d_size); |
| |
| // Resize the data and the section header. |
| data->d_size += hole_size; |
| section_header->sh_size += hole_size; |
| |
| Elf32_Ehdr* elf_header = elf32_getehdr(elf); |
| Elf32_Phdr* elf_program_header = elf32_getphdr(elf); |
| |
| // 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. |
| AdjustElfHeaderForHole(elf_header, hole_start, hole_size); |
| |
| // Adjust all program headers. |
| AdjustProgramHeadersForHole(elf_program_header, |
| elf_header->e_phnum, |
| hole_start, |
| hole_size); |
| |
| // Adjust all section headers. |
| AdjustSectionHeadersForHole(elf, hole_start, hole_size); |
| |
| // We use the dynamic program header entry to locate the dynamic section. |
| const Elf32_Phdr* dynamic_program_header = NULL; |
| |
| // Find the dynamic program header entry. |
| for (size_t i = 0; i < elf_header->e_phnum; ++i) { |
| Elf32_Phdr* program_header = &elf_program_header[i]; |
| |
| if (program_header->p_type == PT_DYNAMIC) { |
| dynamic_program_header = program_header; |
| } |
| } |
| CHECK(dynamic_program_header); |
| |
| // Sections requiring special attention, and the .android.rel.dyn offset. |
| Elf_Scn* dynamic_section = NULL; |
| Elf_Scn* dynsym_section = NULL; |
| Elf_Scn* relplt_section = NULL; |
| Elf_Scn* symtab_section = NULL; |
| Elf32_Off android_rel_dyn_offset = 0; |
| |
| // Find these sections, and the .android.rel.dyn offset. |
| section = NULL; |
| while ((section = elf_nextscn(elf, section)) != NULL) { |
| Elf32_Shdr* section_header = elf32_getshdr(section); |
| std::string name = elf_strptr(elf, string_index, section_header->sh_name); |
| |
| if (section_header->sh_offset == dynamic_program_header->p_offset) { |
| dynamic_section = section; |
| } |
| if (name == ".dynsym") { |
| dynsym_section = section; |
| } |
| if (name == ".rel.plt") { |
| relplt_section = section; |
| } |
| if (name == ".symtab") { |
| symtab_section = section; |
| } |
| |
| // Note .android.rel.dyn offset. |
| if (name == ".android.rel.dyn") { |
| android_rel_dyn_offset = section_header->sh_offset; |
| } |
| } |
| CHECK(dynamic_section != NULL); |
| CHECK(dynsym_section != NULL); |
| CHECK(relplt_section != NULL); |
| CHECK(android_rel_dyn_offset != 0); |
| |
| // Adjust the .dynamic section for the hole. Because we have to edit the |
| // current contents of .dynamic we disallow resizing it. |
| CHECK(section != dynamic_section); |
| AdjustDynamicSectionForHole(dynamic_section, |
| is_rel_dyn_resize, |
| hole_start, |
| hole_size); |
| |
| // Adjust the .dynsym section for the hole. |
| AdjustDynSymSectionForHole(dynsym_section, hole_start, hole_size); |
| |
| // Adjust the .rel.plt section for the hole. |
| AdjustRelPltSectionForHole(relplt_section, hole_start, hole_size); |
| |
| // If present, adjust the .symtab section for the hole. If the shared |
| // library was stripped then .symtab will be absent. |
| if (symtab_section) |
| AdjustSymTabSectionForHole(symtab_section, hole_start, hole_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(Elf32_Dyn dyn, |
| std::vector<Elf32_Dyn>* dynamics) { |
| // Loop until the penultimate entry. We cannot replace the end sentinel. |
| for (size_t i = 0; i < dynamics->size() - 1; ++i) { |
| Elf32_Dyn &slot = dynamics->at(i); |
| if (slot.d_tag == DT_NULL) { |
| slot = dyn; |
| VLOG("dynamic[%lu] overwritten with %u\n", i, dyn.d_tag); |
| return; |
| } |
| } |
| |
| // No free dynamics vector slot was found. |
| LOG("FATAL: No spare dynamic vector slots found " |
| "(to fix, increase gold's --spare-dynamic-tags value)\n"); |
| NOTREACHED(); |
| } |
| |
| // 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(Elf32_Sword tag, |
| std::vector<Elf32_Dyn>* dynamics) { |
| // Loop until the penultimate entry, and never match the end sentinel. |
| for (size_t i = 0; i < dynamics->size() - 1; ++i) { |
| Elf32_Dyn &slot = dynamics->at(i); |
| if (slot.d_tag == tag) { |
| for ( ; i < dynamics->size() - 1; ++i) { |
| dynamics->at(i) = dynamics->at(i + 1); |
| VLOG("dynamic[%lu] overwritten with dynamic[%lu]\n", i, i + 1); |
| } |
| CHECK(dynamics->at(i).d_tag == DT_NULL); |
| return; |
| } |
| } |
| |
| // No matching dynamics vector entry was found. |
| NOTREACHED(); |
| } |
| |
| // Apply R_ARM_RELATIVE relocations to the file data to which they refer. |
| // This relocates data into the area it will occupy after the hole in |
| // .rel.dyn is added or removed. |
| void AdjustRelocationTargets(Elf* elf, |
| Elf32_Off hole_start, |
| size_t hole_size, |
| const std::vector<Elf32_Rel>& relocations) { |
| Elf_Scn* section = NULL; |
| while ((section = elf_nextscn(elf, section)) != NULL) { |
| const Elf32_Shdr* section_header = elf32_getshdr(section); |
| |
| // Identify this section's start and end addresses. |
| const Elf32_Addr section_start = section_header->sh_addr; |
| const Elf32_Addr section_end = section_start + section_header->sh_size; |
| |
| Elf_Data* data = GetSectionData(section); |
| |
| // Ignore sections with no effective data. |
| if (data->d_buf == NULL) |
| continue; |
| |
| // Create a copy-on-write pointer to the section's data. |
| uint8_t* area = reinterpret_cast<uint8_t*>(data->d_buf); |
| |
| for (size_t i = 0; i < relocations.size(); ++i) { |
| const Elf32_Rel* relocation = &relocations[i]; |
| CHECK(ELF32_R_TYPE(relocation->r_info) == R_ARM_RELATIVE); |
| |
| // See if this relocation points into the current section. |
| if (relocation->r_offset >= section_start && |
| relocation->r_offset < section_end) { |
| Elf32_Addr byte_offset = relocation->r_offset - section_start; |
| Elf32_Off* target = reinterpret_cast<Elf32_Off*>(area + byte_offset); |
| |
| // Is the relocation's target after the hole's start? |
| if (*target > hole_start) { |
| // Copy on first write. Recompute target to point into the newly |
| // allocated buffer. |
| if (area == data->d_buf) { |
| area = new uint8_t[data->d_size]; |
| memcpy(area, data->d_buf, data->d_size); |
| target = reinterpret_cast<Elf32_Off*>(area + byte_offset); |
| } |
| |
| *target += hole_size; |
| VLOG("relocation[%lu] target adjusted to %u\n", i, *target); |
| } |
| } |
| } |
| |
| // If we applied any relocation to this section, write it back. |
| if (area != data->d_buf) { |
| RewriteSectionData(data, area, data->d_size); |
| delete [] area; |
| } |
| } |
| } |
| |
| // Pad relocations with a given number of R_ARM_NONE relocations. |
| void PadRelocations(size_t count, |
| std::vector<Elf32_Rel>* relocations) { |
| const Elf32_Rel r_arm_none = {R_ARM_NONE, 0}; |
| std::vector<Elf32_Rel> padding(count, r_arm_none); |
| relocations->insert(relocations->end(), padding.begin(), padding.end()); |
| } |
| |
| // Adjust relocations so that the offset that they indicate will be correct |
| // after the hole in .rel.dyn is added or removed (in effect, relocate the |
| // relocations). |
| void AdjustRelocations(Elf32_Off hole_start, |
| size_t hole_size, |
| std::vector<Elf32_Rel>* relocations) { |
| for (size_t i = 0; i < relocations->size(); ++i) { |
| Elf32_Rel* relocation = &relocations->at(i); |
| if (relocation->r_offset > hole_start) { |
| relocation->r_offset += hole_size; |
| VLOG("relocation[%lu] offset adjusted to %u\n", i, relocation->r_offset); |
| } |
| } |
| } |
| |
| } // namespace |
| |
| // Remove R_ARM_RELATIVE entries from .rel.dyn and write as packed data |
| // into .android.rel.dyn. |
| bool ElfFile::PackRelocations() { |
| // Load the ELF file into libelf. |
| if (!Load()) { |
| LOG("ERROR: Failed to load as ELF (elf_error=%d)\n", elf_errno()); |
| return false; |
| } |
| |
| // Retrieve the current .rel.dyn section data. |
| Elf_Data* data = GetSectionData(rel_dyn_section_); |
| |
| // Convert data to a vector of Elf32 relocations. |
| const Elf32_Rel* relocations_base = reinterpret_cast<Elf32_Rel*>(data->d_buf); |
| std::vector<Elf32_Rel> relocations( |
| relocations_base, |
| relocations_base + data->d_size / sizeof(relocations[0])); |
| |
| std::vector<Elf32_Rel> relative_relocations; |
| std::vector<Elf32_Rel> other_relocations; |
| |
| // Filter relocations into those that are R_ARM_RELATIVE and others. |
| for (size_t i = 0; i < relocations.size(); ++i) { |
| const Elf32_Rel& relocation = relocations[i]; |
| if (ELF32_R_TYPE(relocation.r_info) == R_ARM_RELATIVE) { |
| CHECK(ELF32_R_SYM(relocation.r_info) == 0); |
| relative_relocations.push_back(relocation); |
| } else { |
| other_relocations.push_back(relocation); |
| } |
| } |
| LOG("R_ARM_RELATIVE: %lu entries\n", relative_relocations.size()); |
| LOG("Other : %lu entries\n", other_relocations.size()); |
| LOG("Total : %lu entries\n", relocations.size()); |
| |
| // If no relative relocations then we have nothing packable. Perhaps |
| // the shared object has already been packed? |
| if (relative_relocations.empty()) { |
| LOG("ERROR: No R_ARM_RELATIVE relocations found (already packed?)\n"); |
| return false; |
| } |
| |
| // Unless padding, pre-apply R_ARM_RELATIVE relocations to account for the |
| // hole, and pre-adjust all relocation offsets accordingly. |
| if (!is_padding_rel_dyn_) { |
| // Pre-calculate the size of the hole we will close up when we rewrite |
| // .rel.dyn. We have to adjust relocation addresses to account for this. |
| Elf32_Shdr* section_header = elf32_getshdr(rel_dyn_section_); |
| const Elf32_Off hole_start = section_header->sh_offset; |
| size_t hole_size = |
| relative_relocations.size() * sizeof(relative_relocations[0]); |
| const size_t unaligned_hole_size = hole_size; |
| |
| // Adjust the actual hole size to preserve alignment. |
| hole_size -= hole_size % kPreserveAlignment; |
| LOG("Compaction : %lu bytes\n", hole_size); |
| |
| // Adjusting for alignment may have removed any packing benefit. |
| if (hole_size == 0) { |
| LOG("Too few R_ARM_RELATIVE relocations to pack after alignment\n"); |
| return false; |
| } |
| |
| // Add R_ARM_NONE relocations to other_relocations to preserve alignment. |
| const size_t padding_bytes = unaligned_hole_size - hole_size; |
| CHECK(padding_bytes % sizeof(other_relocations[0]) == 0); |
| const size_t required = padding_bytes / sizeof(other_relocations[0]); |
| PadRelocations(required, &other_relocations); |
| LOG("Alignment pad : %lu relocations\n", required); |
| |
| // Apply relocations to all R_ARM_RELATIVE data to relocate it into the |
| // area it will occupy once the hole in .rel.dyn is removed. |
| AdjustRelocationTargets(elf_, hole_start, -hole_size, relative_relocations); |
| // Relocate the relocations. |
| AdjustRelocations(hole_start, -hole_size, &relative_relocations); |
| AdjustRelocations(hole_start, -hole_size, &other_relocations); |
| } else { |
| // If padding, add R_ARM_NONE 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 required = relocations.size() - other_relocations.size(); |
| PadRelocations(required, &other_relocations); |
| } |
| |
| |
| // Pack R_ARM_RELATIVE relocations. |
| const size_t initial_bytes = |
| relative_relocations.size() * sizeof(relative_relocations[0]); |
| LOG("Unpacked R_ARM_RELATIVE: %lu bytes\n", initial_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("Packed R_ARM_RELATIVE: %lu bytes\n", packed_bytes); |
| |
| // If we have insufficient R_ARM_RELATIVE relocations to form a run then |
| // packing fails. |
| if (packed.empty()) { |
| LOG("Too few R_ARM_RELATIVE relocations to pack\n"); |
| return false; |
| } |
| |
| // Run a loopback self-test as a check that packing is lossless. |
| std::vector<Elf32_Rel> unpacked; |
| packer.UnpackRelativeRelocations(packed, &unpacked); |
| CHECK(unpacked.size() == relative_relocations.size()); |
| for (size_t i = 0; i < unpacked.size(); ++i) { |
| CHECK(unpacked[i].r_offset == relative_relocations[i].r_offset); |
| CHECK(unpacked[i].r_info == relative_relocations[i].r_info); |
| } |
| |
| // Make sure packing saved some space. |
| if (packed_bytes >= initial_bytes) { |
| LOG("Packing R_ARM_RELATIVE relocations saves no space\n"); |
| return false; |
| } |
| |
| // Rewrite the current .rel.dyn section to be only the non-R_ARM_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(elf_, rel_dyn_section_, bytes); |
| RewriteSectionData(data, section_data, bytes); |
| |
| // Rewrite the current .android.rel.dyn section to hold the packed |
| // R_ARM_RELATIVE relocations. |
| data = GetSectionData(android_rel_dyn_section_); |
| ResizeSection(elf_, android_rel_dyn_section_, packed_bytes); |
| RewriteSectionData(data, packed_data, packed_bytes); |
| |
| // Rewrite .dynamic to include two new tags describing .android.rel.dyn. |
| data = GetSectionData(dynamic_section_); |
| const Elf32_Dyn* dynamic_base = reinterpret_cast<Elf32_Dyn*>(data->d_buf); |
| std::vector<Elf32_Dyn> dynamics( |
| dynamic_base, |
| dynamic_base + data->d_size / sizeof(dynamics[0])); |
| Elf32_Shdr* section_header = elf32_getshdr(android_rel_dyn_section_); |
| // Use two of the spare slots to describe the .android.rel.dyn section. |
| const Elf32_Dyn offset_dyn |
| = {DT_ANDROID_ARM_REL_OFFSET, {section_header->sh_offset}}; |
| AddDynamicEntry(offset_dyn, &dynamics); |
| const Elf32_Dyn size_dyn |
| = {DT_ANDROID_ARM_REL_SIZE, {section_header->sh_size}}; |
| AddDynamicEntry(size_dyn, &dynamics); |
| const void* dynamics_data = &dynamics[0]; |
| const size_t dynamics_bytes = dynamics.size() * sizeof(dynamics[0]); |
| RewriteSectionData(data, dynamics_data, dynamics_bytes); |
| |
| Flush(); |
| return true; |
| } |
| |
| // Find packed R_ARM_RELATIVE relocations in .android.rel.dyn, unpack them, |
| // and rewrite the .rel.dyn section in so_file to contain unpacked data. |
| bool ElfFile::UnpackRelocations() { |
| // Load the ELF file into libelf. |
| if (!Load()) { |
| LOG("ERROR: Failed to load as ELF (elf_error=%d)\n", elf_errno()); |
| return false; |
| } |
| |
| // Retrieve the current .android.rel.dyn section data. |
| Elf_Data* data = GetSectionData(android_rel_dyn_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])); |
| |
| // Properly packed data must begin with "APR1". |
| if (packed.empty() || |
| packed[0] != 'A' || packed[1] != 'P' || |
| packed[2] != 'R' || packed[3] != '1') { |
| LOG("ERROR: Packed R_ARM_RELATIVE relocations not found (not packed?)\n"); |
| return false; |
| } |
| |
| // Unpack the data to re-materialize the R_ARM_RELATIVE relocations. |
| const size_t packed_bytes = packed.size() * sizeof(packed[0]); |
| LOG("Packed R_ARM_RELATIVE: %lu bytes\n", packed_bytes); |
| std::vector<Elf32_Rel> relative_relocations; |
| RelocationPacker packer; |
| packer.UnpackRelativeRelocations(packed, &relative_relocations); |
| const size_t unpacked_bytes = |
| relative_relocations.size() * sizeof(relative_relocations[0]); |
| LOG("Unpacked R_ARM_RELATIVE: %lu bytes\n", unpacked_bytes); |
| |
| // Retrieve the current .rel.dyn section data. |
| data = GetSectionData(rel_dyn_section_); |
| |
| // Interpret data as Elf32 relocations. |
| const Elf32_Rel* relocations_base = reinterpret_cast<Elf32_Rel*>(data->d_buf); |
| std::vector<Elf32_Rel> relocations( |
| relocations_base, |
| relocations_base + data->d_size / sizeof(relocations[0])); |
| |
| std::vector<Elf32_Rel> other_relocations; |
| size_t padding = 0; |
| |
| // Filter relocations to locate any that are R_ARM_NONE. These will occur |
| // if padding was turned on for packing. |
| for (size_t i = 0; i < relocations.size(); ++i) { |
| const Elf32_Rel& relocation = relocations[i]; |
| if (ELF32_R_TYPE(relocation.r_info) != R_ARM_NONE) { |
| other_relocations.push_back(relocation); |
| } else { |
| ++padding; |
| } |
| } |
| LOG("R_ARM_RELATIVE: %lu entries\n", relative_relocations.size()); |
| LOG("Other : %lu entries\n", other_relocations.size()); |
| |
| // If we found the same number of R_ARM_NONE entries in .rel.dyn as we |
| // hold as unpacked relative relocations, then this is a padded file. |
| const bool is_padded = padding == relative_relocations.size(); |
| |
| // Unless padded, pre-apply R_ARM_RELATIVE relocations to account for the |
| // hole, and pre-adjust all relocation offsets accordingly. |
| if (!is_padded) { |
| // Pre-calculate the size of the hole we will open up when we rewrite |
| // .rel.dyn. We have to adjust relocation addresses to account for this. |
| Elf32_Shdr* section_header = elf32_getshdr(rel_dyn_section_); |
| const Elf32_Off hole_start = section_header->sh_offset; |
| size_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("Expansion : %lu bytes\n", hole_size); |
| |
| // Apply relocations to all R_ARM_RELATIVE data to relocate it into the |
| // area it will occupy once the hole in .rel.dyn is opened. |
| AdjustRelocationTargets(elf_, hole_start, hole_size, relative_relocations); |
| // Relocate the relocations. |
| AdjustRelocations(hole_start, hole_size, &relative_relocations); |
| AdjustRelocations(hole_start, hole_size, &other_relocations); |
| } |
| |
| // Rewrite the current .rel.dyn section to be the R_ARM_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 .rel.dyn |
| // 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("Total : %lu entries\n", relocations.size()); |
| ResizeSection(elf_, rel_dyn_section_, bytes); |
| RewriteSectionData(data, section_data, bytes); |
| |
| // Nearly empty the current .android.rel.dyn 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. |
| data = GetSectionData(android_rel_dyn_section_); |
| ResizeSection(elf_, android_rel_dyn_section_, sizeof(kStubIdentifier)); |
| RewriteSectionData(data, &kStubIdentifier, sizeof(kStubIdentifier)); |
| |
| // Rewrite .dynamic to remove two tags describing .android.rel.dyn. |
| data = GetSectionData(dynamic_section_); |
| const Elf32_Dyn* dynamic_base = reinterpret_cast<Elf32_Dyn*>(data->d_buf); |
| std::vector<Elf32_Dyn> dynamics( |
| dynamic_base, |
| dynamic_base + data->d_size / sizeof(dynamics[0])); |
| RemoveDynamicEntry(DT_ANDROID_ARM_REL_SIZE, &dynamics); |
| RemoveDynamicEntry(DT_ANDROID_ARM_REL_OFFSET, &dynamics); |
| const void* dynamics_data = &dynamics[0]; |
| const size_t dynamics_bytes = dynamics.size() * sizeof(dynamics[0]); |
| RewriteSectionData(data, 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("elf_update returned: %lu\n", 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 |