X64: Exit frame should use x64 ABI callee-save registers.

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
===================================================================
--- src/x64/codegen-x64.cc	(revision 2348)
+++ src/x64/codegen-x64.cc	(working copy)
@@ -6030,7 +6030,7 @@
   // rbx: pointer to C function  (C callee-saved).
   // rbp: frame pointer  (restored after C call).
   // rsp: stack pointer  (restored after C call).
-  // rdi: number of arguments including receiver.
+  // r14: number of arguments including receiver (C callee-saved).
   // r15: pointer to the first argument (C callee-saved).
   //      This pointer is reused in LeaveExitFrame(), so it is stored in a
   //      callee-saved register.
@@ -6058,11 +6058,11 @@
   // Call C function.
 #ifdef __MSVC__
   // MSVC passes arguments in rcx, rdx, r8, r9
-  __ movq(rcx, rdi);  // argc.
+  __ movq(rcx, r14);  // argc.
   __ movq(rdx, r15);  // argv.
 #else  // ! defined(__MSVC__)
   // GCC passes arguments in rdi, rsi, rdx, rcx, r8, r9.
-  // First argument is already in rdi.
+  __ movq(rdi, r14);  // argc.
   __ movq(rsi, r15);  // argv.
 #endif
   __ call(rbx);
@@ -6204,10 +6204,9 @@
 void CEntryStub::GenerateBody(MacroAssembler* masm, bool is_debug_break) {
   // rax: number of arguments including receiver
   // rbx: pointer to C function  (C callee-saved)
-  // rbp: frame pointer  (restored after C call)
+  // rbp: frame pointer of calling JS frame (restored after C call)
   // rsp: stack pointer  (restored after C call)
-  // rsi: current context (C callee-saved)
-  // rdi: caller's parameter pointer pp  (C callee-saved)
+  // rsi: current context (restored)
 
   // NOTE: Invocations of builtins may return failure objects
   // instead of a proper result. The builtin entry handles
@@ -6221,16 +6220,16 @@
   // Enter the exit frame that transitions from JavaScript to C++.
   __ EnterExitFrame(frame_type);
 
-  // rax: result parameter for PerformGC, if any (setup below).
-  //      Holds the result of a previous call to GenerateCore that
-  //      returned a failure. On next call, it's used as parameter
-  //      to Runtime::PerformGC.
+  // rax: Holds the context at this point, but should not be used.
+  //      On entry to code generated by GenerateCore, it must hold
+  //      a failure result if the collect_garbage argument to GenerateCore
+  //      is true.  This failure result can be the result of code
+  //      generated by a previous call to GenerateCore.  The value
+  //      of rax is then passed to Runtime::PerformGC.
   // rbx: pointer to builtin function  (C callee-saved).
-  // rbp: frame pointer  (restored after C call).
-  // rsp: stack pointer  (restored after C call).
-  // rdi: number of arguments including receiver (destroyed by C call).
-  //      The rdi register is not callee-save in Unix 64-bit ABI, so
-  //      we must treat it as volatile.
+  // rbp: frame pointer of exit frame  (restored after C call).
+  // rsp: stack pointer (restored after C call).
+  // r14: number of arguments including receiver (C callee-saved).
   // r15: argv pointer (C callee-saved).
 
   Label throw_out_of_memory_exception;