| // Copyright 2012 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "courgette/disassembler_elf_32_x86.h" |
| |
| #include <memory> |
| #include <utility> |
| #include <vector> |
| |
| #include "courgette/assembly_program.h" |
| #include "courgette/courgette.h" |
| |
| namespace courgette { |
| |
| CheckBool DisassemblerElf32X86::TypedRVAX86::ComputeRelativeTarget( |
| const uint8_t* op_pointer) { |
| set_relative_target(Read32LittleEndian(op_pointer) + 4); |
| return true; |
| } |
| |
| CheckBool DisassemblerElf32X86::TypedRVAX86::EmitInstruction( |
| Label* label, |
| InstructionReceptor* receptor) { |
| return receptor->EmitRel32(label); |
| } |
| |
| uint16_t DisassemblerElf32X86::TypedRVAX86::op_size() const { |
| return 4; |
| } |
| |
| DisassemblerElf32X86::DisassemblerElf32X86(const uint8_t* start, size_t length) |
| : DisassemblerElf32(start, length) {} |
| |
| // Convert an ELF relocation struction into an RVA. |
| CheckBool DisassemblerElf32X86::RelToRVA(Elf32_Rel rel, RVA* result) const { |
| // The rightmost byte of r_info is the type. |
| elf32_rel_386_type_values type = |
| static_cast<elf32_rel_386_type_values>(rel.r_info & 0xFF); |
| |
| // The other 3 bytes of r_info are the symbol. |
| uint32_t symbol = rel.r_info >> 8; |
| |
| switch (type) { |
| case R_386_NONE: |
| case R_386_32: |
| case R_386_PC32: |
| case R_386_GOT32: |
| case R_386_PLT32: |
| case R_386_COPY: |
| case R_386_GLOB_DAT: |
| case R_386_JMP_SLOT: |
| return false; |
| |
| case R_386_RELATIVE: |
| if (symbol != 0) |
| return false; |
| |
| // This is a basic ABS32 relocation address. |
| *result = rel.r_offset; |
| return true; |
| |
| case R_386_GOTOFF: |
| case R_386_GOTPC: |
| case R_386_TLS_TPOFF: |
| return false; |
| } |
| |
| return false; |
| } |
| |
| CheckBool DisassemblerElf32X86::ParseRelocationSection( |
| const Elf32_Shdr* section_header, |
| InstructionReceptor* receptor) const { |
| // We can reproduce the R_386_RELATIVE entries in one of the relocation table |
| // based on other information in the patch, given these conditions: |
| // |
| // All R_386_RELATIVE entries are: |
| // 1) In the same relocation table |
| // 2) Are consecutive |
| // 3) Are sorted in memory address order |
| // |
| // Happily, this is normally the case, but it's not required by spec, so we |
| // check, and just don't do it if we don't match up. |
| |
| // The expectation is that one relocation section will contain all of our |
| // R_386_RELATIVE entries in the expected order followed by assorted other |
| // entries we can't use special handling for. |
| |
| bool match = true; |
| |
| // Walk all the bytes in the section, matching relocation table or not. |
| FileOffset file_offset = section_header->sh_offset; |
| FileOffset section_end = file_offset + section_header->sh_size; |
| |
| const Elf32_Rel* section_relocs_iter = reinterpret_cast<const Elf32_Rel*>( |
| FileOffsetToPointer(section_header->sh_offset)); |
| |
| uint32_t section_relocs_count = |
| section_header->sh_size / section_header->sh_entsize; |
| |
| if (abs32_locations_.empty()) |
| match = false; |
| |
| if (abs32_locations_.size() > section_relocs_count) |
| match = false; |
| |
| std::vector<RVA>::const_iterator reloc_iter = abs32_locations_.begin(); |
| |
| // Try to match successive reloc units with (sorted) |abs32_locations_|. |
| while (match && (reloc_iter != abs32_locations_.end())) { |
| if (section_relocs_iter->r_info != R_386_RELATIVE || |
| section_relocs_iter->r_offset != *reloc_iter) { |
| match = false; |
| } |
| ++section_relocs_iter; |
| ++reloc_iter; |
| } |
| |
| if (match) { |
| // Success: Emit relocation table. |
| if (!receptor->EmitElfRelocation()) |
| return false; |
| file_offset += sizeof(Elf32_Rel) * abs32_locations_.size(); |
| } |
| |
| return ParseSimpleRegion(file_offset, section_end, receptor); |
| } |
| |
| CheckBool DisassemblerElf32X86::ParseRel32RelocsFromSection( |
| const Elf32_Shdr* section_header) { |
| FileOffset start_file_offset = section_header->sh_offset; |
| FileOffset end_file_offset = start_file_offset + section_header->sh_size; |
| |
| const uint8_t* start_pointer = FileOffsetToPointer(start_file_offset); |
| const uint8_t* end_pointer = FileOffsetToPointer(end_file_offset); |
| |
| // Quick way to convert from Pointer to RVA within a single Section is to |
| // subtract |pointer_to_rva|. |
| const uint8_t* const adjust_pointer_to_rva = |
| start_pointer - section_header->sh_addr; |
| |
| std::vector<RVA>::iterator abs32_pos = abs32_locations_.begin(); |
| |
| // Find the rel32 relocations. |
| const uint8_t* p = start_pointer; |
| while (p < end_pointer) { |
| // Heuristic discovery of rel32 locations in instruction stream: are the |
| // next few bytes the start of an instruction containing a rel32 |
| // addressing mode? |
| const uint8_t* rel32 = nullptr; |
| |
| if (p + 5 <= end_pointer) { |
| if (*p == 0xE8 || *p == 0xE9) { // jmp rel32 and call rel32 |
| rel32 = p + 1; |
| } |
| } |
| if (p + 6 <= end_pointer) { |
| if (*p == 0x0F && (p[1] & 0xF0) == 0x80) { // Jcc long form |
| if (p[1] != 0x8A && p[1] != 0x8B) // JPE/JPO unlikely |
| rel32 = p + 2; |
| } |
| } |
| if (rel32) { |
| RVA rel32_rva = static_cast<RVA>(rel32 - adjust_pointer_to_rva); |
| // Is there an abs32 reloc overlapping the candidate? |
| while (abs32_pos != abs32_locations_.end() && *abs32_pos < rel32_rva - 3) |
| ++abs32_pos; |
| // Now: (*abs32_pos > rel32_rva - 4) i.e. the lowest addressed 4-byte |
| // region that could overlap rel32_rva. |
| if (abs32_pos != abs32_locations_.end()) { |
| if (*abs32_pos < rel32_rva + 4) { |
| // Beginning of abs32 reloc is before end of rel32 reloc so they |
| // overlap. Skip four bytes past the abs32 reloc. |
| RVA current_rva = static_cast<RVA>(p - adjust_pointer_to_rva); |
| p += (*abs32_pos + 4) - current_rva; |
| continue; |
| } |
| } |
| |
| std::unique_ptr<TypedRVAX86> typed_rel32_rva(new TypedRVAX86(rel32_rva)); |
| if (!typed_rel32_rva->ComputeRelativeTarget(rel32)) |
| return false; |
| |
| RVA target_rva = typed_rel32_rva->rva() + |
| typed_rel32_rva->relative_target(); |
| if (IsValidTargetRVA(target_rva)) { |
| rel32_locations_.push_back(std::move(typed_rel32_rva)); |
| #if COURGETTE_HISTOGRAM_TARGETS |
| ++rel32_target_rvas_[target_rva]; |
| #endif |
| p = rel32 + 4; |
| continue; |
| } |
| } |
| p += 1; |
| } |
| |
| return true; |
| } |
| |
| } // namespace courgette |