Add 64-bit absolute address support to courgette.

Turns out, courgette never really understood 64-bit addresses, and they were all being truncated to 32-bit values. This worked fine, as the high 32-bit part was just serialized as byte data, but would have broken for a 64-bit PE image that straddled the 32-bit boundary.

This CL adds a new op code for ABS64 to ensure that 64-bit math is used when assembling them, but re-uses the existing abs32 streams (since RVA are always 32-bit).  This always reduces the size of the patch, but only by a tiny amount, since the four bytes in the absolute addresses no longer need to be stored separately.

This also fixes static cast by reading the 8-byte absolute address from 64-bit binaries.

This change is virtually size neutral.  Against test binaries (64-bit chrome.dll 40.0.2214.115->43.0.2317.0) the uncompressed patch sizes were:

before: 10,948,152
after: 10,925,425 (0.2% reduction)

BUG=419996
TEST=courgette_unittests

Review URL: https://codereview.chromium.org/629643002

Cr-Commit-Position: refs/heads/master@{#320449}

1 files changed, 5 insertions, 6 deletions

diff --git a/courgette/disassembler_win32_x64.cc b/courgette/disassembler_win32_x64.cc
index 626bd35..73ad0b4 100644
--- a/courgette/disassembler_win32_x64.cc
+++ b/courgette/disassembler_win32_x64.cc
@@ -10,6 +10,7 @@
 
 #include "base/basictypes.h"
 #include "base/logging.h"
+#include "base/numerics/safe_conversions.h"
 
 #include "courgette/assembly_program.h"
 #include "courgette/courgette.h"
@@ -568,15 +569,13 @@ CheckBool DisassemblerWin32X64::ParseFileRegion(
       ++abs32_pos;
 
     if (abs32_pos != abs32_locations_.end() && *abs32_pos == current_rva) {
-      uint32 target_address = Read32LittleEndian(p);
-      // TODO(wfh): image_base() can be larger than 32 bits, so this math can
-      // underflow.  Figure out the right solution here.
-      RVA target_rva = target_address - static_cast<uint32>(image_base());
+      uint64 target_address = Read64LittleEndian(p);
+      RVA target_rva = base::checked_cast<RVA>(target_address - image_base());
       // TODO(sra): target could be Label+offset.  It is not clear how to guess
       // which it might be.  We assume offset==0.
-      if (!program->EmitAbs32(program->FindOrMakeAbs32Label(target_rva)))
+      if (!program->EmitAbs64(program->FindOrMakeAbs32Label(target_rva)))
         return false;
-      p += 4;
+      p += 8;
       continue;
     }