Uses an object pool on x64

runtime/vm/debugger_x64.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/debugger.h"
 
 #include "vm/cpu.h"
@@ skipping 24 matching lines @@
   ASSERT(num_actual_args > 0);
   // Stack pointer points to last argument that was pushed on the stack.
   uword closure_addr = sp() + ((num_actual_args - 1) * kWordSize);
   return reinterpret_cast<RawObject*>(
              *reinterpret_cast<uword*>(closure_addr));
 }
 
 
 void CodeBreakpoint::PatchFunctionReturn() {
   uint8_t* code = reinterpret_cast<uint8_t*>(pc_ - 13);
-  // movq %rbp,%rsp
-  ASSERT((code[0] == 0x48) && (code[1] == 0x89) && (code[2] == 0xec));
-  ASSERT(code[3] == 0x5d);  // popq %rbp
-  ASSERT(code[4] == 0xc3);  // ret
-  // Next 8 bytes are nop instructions
-  ASSERT((code[5] == 0x90) && (code[6] == 0x90) &&
-         (code[7] == 0x90) && (code[8] == 0x90) &&
-         (code[9] == 0x90) && (code[10] == 0x90) &&
-         (code[11] == 0x90) && (code[12] == 0x90));
-         // Smash code with call instruction and relative target address.
+  ASSERT((code[0] == 0x4c) && (code[1] == 0x8b) && (code[2] == 0x7d) &&
+         (code[3] == 0xf0));  // movq r15,[rbp-0x10]
+  ASSERT((code[4] == 0x48) && (code[5] == 0x89) &&
+         (code[6] == 0xec));  // mov rsp, rbp
+  ASSERT(code[7] == 0x5d);  // pop rbp
+  ASSERT(code[8] == 0xc3);  // ret
+  ASSERT((code[9] == 0x90) && (code[10] == 0x90) && (code[11] == 0x90) &&
+         (code[12] == 0x90));  // nops
+  // Smash code with call instruction and relative target address.
   uword stub_addr = StubCode::BreakpointReturnEntryPoint();
   code[0] = 0x49;
   code[1] = 0xbb;
   *reinterpret_cast<uword*>(&code[2]) = stub_addr;
   code[10] = 0x41;
   code[11] = 0xff;
   code[12] = 0xd3;
   CPU::FlushICache(pc_ - 13, 13);
 }
 
 
 void CodeBreakpoint::RestoreFunctionReturn() {
   uint8_t* code = reinterpret_cast<uint8_t*>(pc_ - 13);
   ASSERT((code[0] == 0x49) && (code[1] == 0xbb));
-  code[0] = 0x48;  // movq %rbp,%rsp
-  code[1] = 0x89;
-  code[2] = 0xec;
-  code[3] = 0x5d;  // popq %rbp
-  code[4] = 0xc3;  // ret
-  code[5] = 0x90;  // nop
-  code[6] = 0x90;  // nop
-  code[7] = 0x90;  // nop
-  code[8] = 0x90;  // nop
-  code[9] = 0x90;  // nop
+  code[0] = 0x4c;  // movq r15,[rbp-0x10]

[Florian Schneider, 2013/09/04 09:39:47]

I know it was this way before, but wouldn't it be much nicer if we used our own
assembler to emit this code?

[zra, 2013/09/04 21:00:41]

Yes. Perhaps for another CL.

+  code[1] = 0x8b;
+  code[2] = 0x7d;
+  code[3] = 0xf0;
+  code[4] = 0x48;  // mov rsp, rbp
+  code[5] = 0x89;
+  code[6] = 0xec;
+  code[7] = 0x5d;  // pop rbp
+  code[8] = 0xc3;  // ret
+  code[9] = 0x90;
   code[10] = 0x90;  // nop
   code[11] = 0x90;  // nop
   code[12] = 0x90;  // nop
   CPU::FlushICache(pc_ - 13, 13);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64