Courgette: Add static method QuickDetect() to optimize program detection.

courgette/disassembler_elf_32.cc

 // 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 <iterator>
 #include <utility>
 
@@ skipping 25 matching lines @@
 
 DisassemblerElf32::Elf32RvaVisitor_Rel32::Elf32RvaVisitor_Rel32(
     const std::vector<std::unique_ptr<TypedRVA>>& rva_locations)
     : VectorRvaVisitor<std::unique_ptr<TypedRVA>>(rva_locations) {
 }
 
 RVA DisassemblerElf32::Elf32RvaVisitor_Rel32::Get() const {
   return (*it_)->rva() + (*it_)->relative_target();
 }
 
-DisassemblerElf32::DisassemblerElf32(const void* start, size_t length)
+DisassemblerElf32::DisassemblerElf32(const uint8_t* start, size_t length)
     : Disassembler(start, length),
       header_(nullptr),
       section_header_table_size_(0),
       program_header_table_(nullptr),
       program_header_table_size_(0),
-      default_string_section_(nullptr) {
-}
+      default_string_section_(nullptr) {}
 
 RVA DisassemblerElf32::FileOffsetToRVA(FileOffset offset) const {
   // File offsets can be 64-bit values, but we are dealing with 32-bit
   // executables and so only need to support 32-bit file sizes.
   uint32_t offset32 = static_cast<uint32_t>(offset);
 
   // Visit section headers ordered by file offset.
   for (Elf32_Half section_id : section_header_file_offset_order_) {
     const Elf32_Shdr* section_header = SectionHeader(section_id);
     // These can appear to have a size in the file, but don't.
@@ skipping 203 matching lines @@
     name->clear();
   } else {
     if (string_pos >= default_string_section_size_)
       return false;
     // Safe because string section must terminate with null.
     *name = default_string_section_ + string_pos;
   }
   return true;
 }
 
+bool DisassemblerElf32::QuickDetect(const uint8_t* start,

[huangs, 2016/06/13 18:30:28]

NIT:
// static

Also, move to Line 218 to match .h file ordering?

[etiennep, 2016/06/14 21:16:37]

Done.

+                                    size_t length,
+                                    e_machine_values elf_em) {
+  if (length < sizeof(Elf32_Ehdr))
+    return false;
+
+  const Elf32_Ehdr* header = reinterpret_cast<const 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 false;
+
+  if (header->e_type != ET_EXEC && header->e_type != ET_DYN)
+    return false;
+  if (header->e_machine != elf_em)
+    return false;
+  if (header->e_version != 1)
+    return false;
+  if (header->e_shentsize != sizeof(Elf32_Shdr))
+    return false;
+
+  return true;
+}
+
 CheckBool DisassemblerElf32::RVAsToFileOffsets(
     const std::vector<RVA>& rvas,
     std::vector<FileOffset>* file_offsets) {
   file_offsets->clear();
   file_offsets->reserve(rvas.size());
   for (RVA rva : rvas) {
     FileOffset file_offset = RVAToFileOffset(rva);
     if (file_offset == kNoFileOffset)
       return false;
     file_offsets->push_back(file_offset);
@@ skipping 312 matching lines @@
     if (!ParseRel32RelocsFromSection(section_header))
       return false;
   }
   if (!found_rel32)
     VLOG(1) << "Warning: Found no rel32 addresses. Missing .text section?";
 
   return true;
 }
 
 }  // namespace courgette