Print stop message.

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
===================================================================
--- runtime/vm/assembler_x64.cc	(revision 3058)
+++ runtime/vm/assembler_x64.cc	(working copy)
@@ -9,9 +9,13 @@
 #include "vm/heap.h"
 #include "vm/memory_region.h"
 #include "vm/runtime_entry.h"
+#include "vm/stub_code.h"
 
 namespace dart {
 
+DEFINE_FLAG(bool, print_stop_message, true, "Print stop message.");
+
+
 void Assembler::InitializeMemoryWithBreakpoints(uword data, int length) {
   memset(reinterpret_cast<void*>(data), Instr::kBreakPointInstruction, length);
 }
@@ -1302,10 +1306,15 @@
 
 
 void Assembler::Stop(const char* message) {
+  int64_t message_address = reinterpret_cast<int64_t>(message);
+  if (FLAG_print_stop_message) {
+    pushq(Immediate(message_address));
+    call(&StubCode::PrintStopMessageLabel());
+    popq(RAX);

[Ivan Posva, 2012/01/09 17:26:42]

This kills the content of RAX.

How about:
pushq(RAX);
movq(RAX, Immediate(message_address));
call(&StubCode::PrintStopMessageLabel());
popq(RAX);

And the stub expects the parameter value in RAX?

[regis, 2012/01/10 00:09:16]

Done. Using RDI instead of RAX and also preserving TMP, which is used by the
pseudo call instruction.

+  }
   // Emit the lower half and the higher half of the message address as immediate
   // operands in the test rax instructions, followed by the int3 instruction.
   // Execution can be resumed with the 'cont' command in gdb.
-  int64_t message_address = reinterpret_cast<int64_t>(message);
   testl(RAX, Immediate(Utils::Low32Bits(message_address)));
   testl(RAX, Immediate(Utils::High32Bits(message_address)));
   int3();