commit f3ac6dd441fc6432c51296c12da99829cf2f1ed8
author huangs <huangs@chromium.org> Wed Mar 22 06:52:24 2017
committer Commit bot <commit-bot@chromium.org> Wed Mar 22 06:52:24 2017
tree 53aaead791a5ca6cd6bfb42410cb7e323bf91aa0
parent a1a68a07774705b75a7cff019c42d3edebf1d04d

[Courgette] Fix ELF reference sorting.

This CL addresses 2 reference sorting issues in DisassemblerElf32:

(1) Bug fix: In ParseFile(), |abs32_locations_| (RVAs) is translated to
    |abs_offsets| (file offsets), but we sort |abs32_locations_|, which
    is redundant. Actually we should sort |abs_offsets|.
(2) Cleanup: |rel32_relocations_| stores rel32 references sorted by
    RVA, but in ParseFile() we re-sort these in offset order. Previously
    Disassemble() optimizes away redundant sorts, but this makes the
    code less robust. We de-optimize this a little potentially redundant
    sort-by-RVA, to assert that |rel32_locations_| is sorted by RVA
    outside of ParseFile().

This CL also makes Disassemble() more uniform, to prepare for
refactoring in a follow-up. Meanwhile, DisassemblerWin32 does not
experience issue since it assumes RVA order is same as file offset
order (this assumption has not has not caused problems so far).

BUG=660980

Review-Url: https://codereview.chromium.org/2744373004
Cr-Original-Commit-Position: refs/heads/master@{#458650}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c615c911eea856986f8daaab73b7f30860234009

disassembler_elf_32.cc

diff --git a/disassembler_elf_32.cc b/disassembler_elf_32.cc
index e305b4c..e35a3af 100644
--- a/disassembler_elf_32.cc
+++ b/disassembler_elf_32.cc
@@ -181,13 +181,6 @@
     return false;
   }
 
-  // Finally sort rel32 locations.
-  std::sort(rel32_locations_.begin(),
-            rel32_locations_.end(),
-            TypedRVA::IsLessThanByRVA);
-  DCHECK(rel32_locations_.empty() ||
-         rel32_locations_.back()->rva() != kUnassignedRVA);
-
   program->DefaultAssignIndexes();
   return true;
 }
@@ -384,6 +377,11 @@
   if (!found_rel32)
     VLOG(1) << "Warning: Found no rel32 addresses. Missing .text section?";
 
+  std::sort(rel32_locations_.begin(), rel32_locations_.end(),
+            TypedRVA::IsLessThanByRVA);
+  DCHECK(rel32_locations_.empty() ||
+         rel32_locations_.back()->rva() != kUnassignedRVA);
+
   return true;
 }
 
@@ -418,15 +416,18 @@
   // Walk all the bytes in the file, whether or not in a section.
   FileOffset file_offset = 0;
 
-  std::vector<FileOffset> abs_offsets;
-
   // File parsing follows file offset order, and we visit abs32 and rel32
   // locations in lockstep. Therefore we need to extract and sort file offsets
-  // of all abs32 and rel32 locations.
+  // of all abs32 and rel32 locations. For abs32, we copy the offsets to a new
+  // array.
+  std::vector<FileOffset> abs_offsets;
   if (!RVAsToFileOffsets(abs32_locations_, &abs_offsets))
     return false;
-  std::sort(abs32_locations_.begin(), abs32_locations_.end());
+  std::sort(abs_offsets.begin(), abs_offsets.end());
 
+  // For rel32, TypedRVA (rather than raw offset) is stored, so sort-by-offset
+  // is performed in place to save memory. At the end of function we will
+  // sort-by-RVA.
   if (!RVAsToFileOffsets(&rel32_locations_))
     return false;
   std::sort(rel32_locations_.begin(),
@@ -496,6 +497,10 @@
   if (!ParseSimpleRegion(file_offset, length(), receptor))
     return false;
 
+  // Restore original rel32 location order and sort by RVA order.
+  std::sort(rel32_locations_.begin(), rel32_locations_.end(),
+            TypedRVA::IsLessThanByRVA);
+
   // Make certain we consume all of the relocations as expected
   return (current_abs_offset == end_abs_offset);
 }