1 files changed, 462 insertions, 0 deletions
diff --git a/courgette/disassembler_elf_32.cc b/courgette/disassembler_elf_32.cc
new file mode 100644
index 0000000..bd49ff1
--- /dev/null
+++ b/courgette/disassembler_elf_32.cc
@@ -0,0 +1,462 @@
+// Copyright 2013 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.
+
+#include "courgette/disassembler_elf_32.h"
+
+#include <algorithm>
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+
+#include "courgette/assembly_program.h"
+#include "courgette/courgette.h"
+#include "courgette/encoded_program.h"
+
+namespace courgette {
+
+DisassemblerElf32::DisassemblerElf32(const void* start, size_t length)
+  : Disassembler(start, length),
+    header_(NULL),
+    section_header_table_(NULL),
+    section_header_table_size_(0),
+    program_header_table_(NULL),
+    program_header_table_size_(0),
+    default_string_section_(NULL) {
+}
+
+bool DisassemblerElf32::ParseHeader() {
+  if (length() < sizeof(Elf32_Ehdr))
+    return Bad("Too small");
+
+  header_ = (Elf32_Ehdr *)start();
+
+  // Have magic for elf header?
+  if (header_->e_ident[0] != 0x7f ||
+      header_->e_ident[1] != 'E' ||
+      header_->e_ident[2] != 'L' ||
+      header_->e_ident[3] != 'F')
+    return Bad("No Magic Number");
+
+  if (header_->e_type != ET_EXEC &&
+      header_->e_type != ET_DYN)
+    return Bad("Not an executable file or shared library");
+
+  if (header_->e_machine != ElfEM())
+    return Bad("Not a supported architecture");
+
+  if (header_->e_version != 1)
+    return Bad("Unknown file version");
+
+  if (header_->e_shentsize != sizeof(Elf32_Shdr))
+    return Bad("Unexpected section header size");
+
+  if (header_->e_shoff >= length())
+    return Bad("Out of bounds section header table offset");
+
+  section_header_table_ = (Elf32_Shdr *)OffsetToPointer(header_->e_shoff);
+  section_header_table_size_ = header_->e_shnum;
+
+  if ((header_->e_shoff + header_->e_shnum ) >= length())
+    return Bad("Out of bounds section header table");
+
+  if (header_->e_phoff >= length())
+    return Bad("Out of bounds program header table offset");
+
+  program_header_table_ = (Elf32_Phdr *)OffsetToPointer(header_->e_phoff);
+  program_header_table_size_ = header_->e_phnum;
+
+  if ((header_->e_phoff + header_->e_phnum) >= length())
+    return Bad("Out of bounds program header table");
+
+  default_string_section_ = (const char *)SectionBody((int)header_->e_shstrndx);
+
+  ReduceLength(DiscoverLength());
+
+  return Good();
+}
+
+bool DisassemblerElf32::Disassemble(AssemblyProgram* target) {
+  if (!ok())
+    return false;
+
+  // The Image Base is always 0 for ELF Executables
+  target->set_image_base(0);
+
+  if (!ParseAbs32Relocs())
+    return false;
+
+  if (!ParseRel32RelocsFromSections())
+    return false;
+
+  if (!ParseFile(target))
+    return false;
+
+  target->DefaultAssignIndexes();
+
+  return true;
+}
+
+uint32 DisassemblerElf32::DiscoverLength() {
+  uint32 result = 0;
+
+  // Find the end of the last section
+  for (int section_id = 0; section_id < SectionHeaderCount(); section_id++) {
+    const Elf32_Shdr *section_header = SectionHeader(section_id);
+
+    if (section_header->sh_type == SHT_NOBITS)
+      continue;
+
+    uint32 section_end = section_header->sh_offset + section_header->sh_size;
+
+    if (section_end > result)
+      result = section_end;
+  }
+
+  // Find the end of the last segment
+  for (int i = 0; i < ProgramSegmentHeaderCount(); i++) {
+    const Elf32_Phdr *segment_header = ProgramSegmentHeader(i);
+
+    uint32 segment_end = segment_header->p_offset + segment_header->p_filesz;
+
+    if (segment_end > result)
+      result = segment_end;
+  }
+
+  uint32 section_table_end = header_->e_shoff +
+                             (header_->e_shnum * sizeof(Elf32_Shdr));
+  if (section_table_end > result)
+    result = section_table_end;
+
+  uint32 segment_table_end = header_->e_phoff +
+                             (header_->e_phnum * sizeof(Elf32_Phdr));
+  if (segment_table_end > result)
+    result = segment_table_end;
+
+  return result;
+}
+
+CheckBool DisassemblerElf32::IsValidRVA(RVA rva) const {
+
+  // It's valid if it's contained in any program segment
+  for (int i = 0; i < ProgramSegmentHeaderCount(); i++) {
+    const Elf32_Phdr *segment_header = ProgramSegmentHeader(i);
+
+    if (segment_header->p_type != PT_LOAD)
+      continue;
+
+    Elf32_Addr begin = segment_header->p_vaddr;
+    Elf32_Addr end = segment_header->p_vaddr + segment_header->p_memsz;
+
+    if (rva >= begin && rva < end)
+      return true;
+  }
+
+  return false;
+}
+
+// Returns RVA for an in memory address, or NULL.
+CheckBool DisassemblerElf32::RVAToFileOffset(Elf32_Addr addr,
+                                                size_t* result) const {
+
+  for (int i = 0; i < ProgramSegmentHeaderCount(); i++) {
+    Elf32_Addr begin = ProgramSegmentMemoryBegin(i);
+    Elf32_Addr end = begin + ProgramSegmentMemorySize(i);
+
+    if (addr >= begin  && addr < end) {
+      Elf32_Addr offset = addr - begin;
+
+      if (offset < ProgramSegmentFileSize(i)) {
+        *result = ProgramSegmentFileOffset(i) + offset;
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+RVA DisassemblerElf32::FileOffsetToRVA(size_t offset) const {
+  // File offsets can be 64 bit values, but we are dealing with 32
+  // bit executables and so only need to support 32bit file sizes.
+  uint32 offset32 = (uint32)offset;
+
+  for (int i = 0; i < SectionHeaderCount(); i++) {
+
+    const Elf32_Shdr *section_header = SectionHeader(i);
+
+    // These can appear to have a size in the file, but don't.
+    if (section_header->sh_type == SHT_NOBITS)
+      continue;
+
+    Elf32_Off section_begin = section_header->sh_offset;
+    Elf32_Off section_end = section_begin + section_header->sh_size;
+
+    if (offset32 >= section_begin && offset32 < section_end) {
+      return section_header->sh_addr + (offset32 - section_begin);
+    }
+  }
+
+  return 0;
+}
+
+CheckBool DisassemblerElf32::RVAsToOffsets(std::vector<RVA>* rvas,
+                                              std::vector<size_t>* offsets) {
+  offsets->clear();
+
+  for (std::vector<RVA>::iterator rva = rvas->begin();
+       rva != rvas->end();
+       rva++) {
+
+    size_t offset;
+
+    if (!RVAToFileOffset(*rva, &offset))
+      return false;
+
+    offsets->push_back(offset);
+  }
+
+  return true;
+}
+
+CheckBool DisassemblerElf32::ParseFile(AssemblyProgram* program) {
+  // Walk all the bytes in the file, whether or not in a section.
+  uint32 file_offset = 0;
+
+  std::vector<size_t> abs_offsets;
+  std::vector<size_t> rel_offsets;
+
+  if (!RVAsToOffsets(&abs32_locations_, &abs_offsets))
+    return false;
+
+  if (!RVAsToOffsets(&rel32_locations_, &rel_offsets))
+    return false;
+
+  std::vector<size_t>::iterator current_abs_offset = abs_offsets.begin();
+  std::vector<size_t>::iterator current_rel_offset = rel_offsets.begin();
+
+  std::vector<size_t>::iterator end_abs_offset = abs_offsets.end();
+  std::vector<size_t>::iterator end_rel_offset = rel_offsets.end();
+
+  for (int section_id = 0;
+       section_id < SectionHeaderCount();
+       section_id++) {
+
+    const Elf32_Shdr *section_header = SectionHeader(section_id);
+
+    if (!ParseSimpleRegion(file_offset,
+                           section_header->sh_offset,
+                           program))
+      return false;
+    file_offset = section_header->sh_offset;
+
+    switch (section_header->sh_type) {
+      case SHT_REL:
+        if (!ParseRelocationSection(section_header, program))
+          return false;
+        file_offset = section_header->sh_offset + section_header->sh_size;
+        break;
+      case SHT_PROGBITS:
+        if (!ParseProgbitsSection(section_header,
+                                  &current_abs_offset, end_abs_offset,
+                                  &current_rel_offset, end_rel_offset,
+                                  program))
+          return false;
+        file_offset = section_header->sh_offset + section_header->sh_size;
+        break;
+      case SHT_NOBITS:
+        // Fall through
+      case SHT_INIT_ARRAY:
+        // Fall through
+      case SHT_FINI_ARRAY:
+        while (current_abs_offset != end_abs_offset &&
+               *current_abs_offset >= section_header->sh_offset &&
+               *current_abs_offset <
+               (section_header->sh_offset + section_header->sh_size)) {
+          // Skip any abs_offsets appear in the unsupported INIT_ARRAY section
+          VLOG(1) << "Skipping relocation entry for unsupported section: " <<
+            section_header->sh_type;
+          current_abs_offset++;
+        }
+        break;
+      default:
+        if (current_abs_offset != end_abs_offset &&
+               *current_abs_offset >= section_header->sh_offset &&
+               *current_abs_offset <
+               (section_header->sh_offset + section_header->sh_size))
+          VLOG(1) << "Relocation address in unrecognized ELF section: " << \
+            section_header->sh_type;
+      break;
+    }
+  }
+
+  // Rest of the file past the last section
+  if (!ParseSimpleRegion(file_offset,
+                         length(),
+                         program))
+    return false;
+
+  // Make certain we consume all of the relocations as expected
+  return (current_abs_offset == end_abs_offset);
+}
+
+CheckBool DisassemblerElf32::ParseProgbitsSection(
+    const Elf32_Shdr *section_header,
+    std::vector<size_t>::iterator* current_abs_offset,
+    std::vector<size_t>::iterator end_abs_offset,
+    std::vector<size_t>::iterator* current_rel_offset,
+    std::vector<size_t>::iterator end_rel_offset,
+    AssemblyProgram* program) {
+
+  // Walk all the bytes in the file, whether or not in a section.
+  size_t file_offset = section_header->sh_offset;
+  size_t section_end = section_header->sh_offset + section_header->sh_size;
+
+  Elf32_Addr origin = section_header->sh_addr;
+  size_t origin_offset = section_header->sh_offset;
+  if (!program->EmitOriginInstruction(origin))
+    return false;
+
+  while (file_offset < section_end) {
+
+    if (*current_abs_offset != end_abs_offset &&
+        file_offset > **current_abs_offset)
+      return false;
+
+    while (*current_rel_offset != end_rel_offset &&
+           file_offset > **current_rel_offset) {
+      (*current_rel_offset)++;
+    }
+
+    size_t next_relocation = section_end;
+
+    if (*current_abs_offset != end_abs_offset &&
+        next_relocation > **current_abs_offset)
+      next_relocation = **current_abs_offset;
+
+    // Rel offsets are heuristically derived, and might (incorrectly) overlap
+    // an Abs value, or the end of the section, so +3 to make sure there is
+    // room for the full 4 byte value.
+    if (*current_rel_offset != end_rel_offset &&
+        next_relocation > (**current_rel_offset + 3))
+      next_relocation = **current_rel_offset;
+
+    if (next_relocation > file_offset) {
+      if (!ParseSimpleRegion(file_offset, next_relocation, program))
+        return false;
+
+      file_offset = next_relocation;
+      continue;
+    }
+
+    if (*current_abs_offset != end_abs_offset &&
+        file_offset == **current_abs_offset) {
+
+      const uint8* p = OffsetToPointer(file_offset);
+      RVA target_rva = Read32LittleEndian(p);
+
+      if (!program->EmitAbs32(program->FindOrMakeAbs32Label(target_rva)))
+        return false;
+      file_offset += sizeof(RVA);
+      (*current_abs_offset)++;
+      continue;
+    }
+
+    if (*current_rel_offset != end_rel_offset &&
+        file_offset == **current_rel_offset) {
+
+      const uint8* p = OffsetToPointer(file_offset);
+      uint32 relative_target = Read32LittleEndian(p);
+      // This cast is for 64 bit systems, and is only safe because we
+      // are working on 32 bit executables.
+      RVA target_rva = (RVA)(origin + (file_offset - origin_offset) +
+                             4 + relative_target);
+
+      if (!program->EmitRel32(program->FindOrMakeRel32Label(target_rva)))
+        return false;
+      file_offset += sizeof(RVA);
+      (*current_rel_offset)++;
+      continue;
+    }
+  }
+
+  // Rest of the section (if any)
+  return ParseSimpleRegion(file_offset, section_end, program);
+}
+
+CheckBool DisassemblerElf32::ParseSimpleRegion(
+    size_t start_file_offset,
+    size_t end_file_offset,
+    AssemblyProgram* program) {
+
+  const uint8* start = OffsetToPointer(start_file_offset);
+  const uint8* end = OffsetToPointer(end_file_offset);
+
+  const uint8* p = start;
+
+  while (p < end) {
+    if (!program->EmitByteInstruction(*p))
+      return false;
+    ++p;
+  }
+
+  return true;
+}
+
+CheckBool DisassemblerElf32::ParseAbs32Relocs() {
+  abs32_locations_.clear();
+
+  // Loop through sections for relocation sections
+  for (int section_id = 0; section_id < SectionHeaderCount(); section_id++) {
+    const Elf32_Shdr *section_header = SectionHeader(section_id);
+
+    if (section_header->sh_type == SHT_REL) {
+
+      Elf32_Rel *relocs_table = (Elf32_Rel *)SectionBody(section_id);
+
+      int relocs_table_count = section_header->sh_size /
+                               section_header->sh_entsize;
+
+      // Elf32_Word relocation_section_id = section_header->sh_info;
+
+      // Loop through relocation objects in the relocation section
+      for (int rel_id = 0; rel_id < relocs_table_count; rel_id++) {
+        RVA rva;
+
+        // Quite a few of these conversions fail, and we simply skip
+        // them, that's okay.
+        if (RelToRVA(relocs_table[rel_id], &rva))
+          abs32_locations_.push_back(rva);
+      }
+    }
+  }
+
+  std::sort(abs32_locations_.begin(), abs32_locations_.end());
+  return true;
+}
+
+CheckBool DisassemblerElf32::ParseRel32RelocsFromSections() {
+
+  rel32_locations_.clear();
+
+  // Loop through sections for relocation sections
+  for (int section_id = 0;
+       section_id < SectionHeaderCount();
+       section_id++) {
+
+    const Elf32_Shdr *section_header = SectionHeader(section_id);
+
+    if (section_header->sh_type != SHT_PROGBITS)
+      continue;
+
+    if (!ParseRel32RelocsFromSection(section_header))
+      return false;
+  }
+
+  std::sort(rel32_locations_.begin(), rel32_locations_.end());
+  return true;
+}
+
+}  // namespace courgette