Implements a new API to set a function entry hook for profiling.

src/arm/code-stubs-arm.cc

Index: src/arm/code-stubs-arm.cc
diff --git a/src/arm/code-stubs-arm.cc b/src/arm/code-stubs-arm.cc
index 169a032fb030c242448f4d491174348cc892a5ad..6f95889bfbb65f0c20d3e87a9f9744ab3f4444fd 100644
--- a/src/arm/code-stubs-arm.cc
+++ b/src/arm/code-stubs-arm.cc
@@ -7513,6 +7513,34 @@ void StoreArrayLiteralElementStub::Generate(MacroAssembler* masm) {
   __ Ret();
 }
 
+
+void ProfileEntryHookStub::Generate(MacroAssembler* masm) {
+  __ stop("foo");
+
+  // Save volatile registers, note that lr is already saved by the caller,
+  // so we need to save an odd number here to keep the stack aligned.
+  __ Push(lr, r1, r0);

[danno, 2012/07/10 09:37:13]

In general, you can't make guarantees about stack alignment within generated
code. We align on the way into C code in the CEntryStub, but since you don't use
that, you will actually have to handle both cases, the aligned and unaligned,
here if you expect the callee to have an aligned stack. 

[Sigurður Ásgeirsson, 2012/07/11 14:50:34]

Done.

+
+  // TODO(siggi): Grab a timer somehow into r2/r3.
+
+  // Our return address, lr, points three instructions (12 bytes) into the
+  // function. Grab that for the first argument to the hook.
+  __ sub(r0, lr, Operand(0xC));

[danno, 2012/07/10 09:37:13]

Define constants for this.

[Sigurður Ásgeirsson, 2012/07/11 14:50:34]

Done.

+  // The caller's return address is 12 bytes up on the stack. Grab that
+  // for the second argument to the hook.
+  __ add(r1, sp, Operand(0x0C));

[danno, 2012/07/10 09:37:13]

Is it possible to use an existing constant in frames-arm.h for this?

[Sigurður Ásgeirsson, 2012/07/11 14:50:34]

This stub is called pre-frame generation, and doesn't itself create a regular
stack frame - added a constant.

+
+  ApiFunction dispatcher(
+      reinterpret_cast<Address>(V8::GetFunctionEntryHookDispatcher()));

[danno, 2012/07/10 09:37:13]

If you really need the dispatcher for ARM only, then it should just be part of
the ARM implementation and not exposed through the API. I am not sure why you
need the indirect dispatch, I think you can just use:

mov(pc, target_reg, LeaveCC, al);?

[Sigurður Ásgeirsson, 2012/07/11 14:50:34]

This is for the simulator.
The simulator only forwards to functions that are tagged as an external
reference, and I couldn't figure a clean way to hook into that to dispatch
straight to the entry hook function.

The dispatcher function is in internal::V8 - I gather this is the
interface/implementation layer between the API and the internals?

I didn't notice any other data members in that namespace/class, but it would be
simpler and perhaps cleaner to declare the function pointer in that namespace
and to manipulate and access it directly?

+  __ mov(ip, Operand(ExternalReference(&dispatcher,
+                                       ExternalReference::BUILTIN_CALL,
+                                       masm->isolate())));
+  __ Call(ip);
+  __ Pop(lr, r1, r0);
+  
+  __ Ret();
+}
+
 #undef __
 
 } }  // namespace v8::internal