Fix potential overwriting of debug jumps of following code.

src/x64/assembler-x64.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 898 matching lines @@
   positions_recorder()->WriteRecordedPositions();
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;
   // Opcode: FF /2 m64.
   emit_optional_rex_32(op);
   emit(0xFF);
   emit_operand(0x2, op);
 }
 
 
+void Assembler::call(Address target) {

[Kevin Millikin (Chromium), 2011/02/04 11:34:54]

Since this function is not entirely safe, the comment from the header should be
repeated here (to guard against someone checking the .cc file, seeing it's
implemented, and using it).

I wonder if we just give it a RelocInfo::Mode so it would generally work?

[Lasse Reichstein, 2011/02/04 12:32:13]

Comment moved.

The RelocInfo::Mode is a little tricky, since we (so far only) use the
instruction during patching, where relocinfo doesn't work anyway.
Suggestions welcome.
Using RelocInfo::INTERNAL_REFERENCE seems the correct thing, but it's used for
absolute references, not relative.

[Kevin Millikin (Chromium), 2011/02/04 12:58:24]

To be clear, I thought the comment should be duplicated so that it occurs in
both places.

[Lasse Reichstein, 2011/02/04 13:04:11]

My bad. That was indeed what I did, but not what I wrote that I had done.

+  positions_recorder()->WriteRecordedPositions();
+  EnsureSpace ensure_space(this);
+  last_pc_ = pc_;
+  // 1110 1000 #32-bit disp.
+  emit(0xE8);
+  Address source = pc_ + 4;
+  intptr_t displacement = target - source;
+  ASSERT(is_int32(displacement));
+  emitl(static_cast<int32_t>(displacement));
+}
+
+
 void Assembler::clc() {
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;
   emit(0xF8);
 }
 
 void Assembler::cdq() {
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;
   emit(0x99);
@@ skipping 2160 matching lines @@
   // specially coded on x64 means that it is a relative 32 bit address, as used
   // by branch instructions.
   return (1 << rmode_) & kApplyMask;
 }
 
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64