Hello all.
I can't understand how the next construction works.
We have two builtins - JSEntryTrampoline and Call
They are called sequentially.
First we build frame in JSEntryTrampoline:
// Current stack contents:
// [rsp + 2 * kPointerSize ... ] : Internal frame
// [rsp + kPointerSize] : function
// [rsp] : receiver
// Current register contents:
// rax : argc
// rbx : argv
// rsi : context
// rdi : function
// rdx : new.target
// Check if we have enough stack space to push all arguments.
// Expects argument count in rax. Clobbers rcx, r11.
Generate_CheckStackOverflow(masm, kRaxIsUntaggedInt);
// Copy arguments to the stack in a loop.
// Register rbx points to array of pointers to handle locations.
// Push the values of these handles.
Label loop, entry;
__ Set(rcx, 0); // Set loop variable to 0.
__ jmp(&entry, Label::kNear);
__ bind(&loop);
__ movp(kScratchRegister, Operand(rbx, rcx, times_pointer_size, 0));
__ Push(Operand(kScratchRegister, 0)); // dereference handle
__ addp(rcx, Immediate(1));
__ bind(&entry);
__ cmpp(rcx, rax);
__ j(not_equal, &loop);
// Invoke the builtin code.
Handle<Code> builtin = is_construct
? masm->isolate()->builtins()->Construct()
: masm->isolate()->builtins()->Call();
__ Call(builtin, RelocInfo::CODE_TARGET);
// Exit the internal frame. Notice that this also removes the empty
// context and the function left on the stack by the code
// invocation.
}
// TODO(X64): Is argument correct? Is there a receiver to remove?
__ ret(1 * kPointerSize); // Remove receiver.
}
The stack is :
arg N - 1
arg N - 2
...
arg 0
receiver
new_target
Ok, we call the Call built next:
void Builtins::Generate_Call(MacroAssembler* masm, ConvertReceiverMode mode,
TailCallMode tail_call_mode) {
// ----------- S t a t e -------------
// -- rax : the number of arguments (not including the receiver)
// -- rdi : the target to call (can be any Object)
// -----------------------------------
StackArgumentsAccessor args(rsp, rax);
Label non_callable, non_function, non_smi;
__ JumpIfSmi(rdi, &non_callable);
__ bind(&non_smi);
__ CmpObjectType(rdi, JS_FUNCTION_TYPE, rcx);
__ j(equal, masm->isolate()->builtins()->CallFunction(mode, tail_call_mode
),
RelocInfo::CODE_TARGET);
__ CmpInstanceType(rcx, JS_BOUND_FUNCTION_TYPE);
__ j(equal, masm->isolate()->builtins()->CallBoundFunction(tail_call_mode
),
RelocInfo::CODE_TARGET);
// Check if target has a [[Call]] internal method.
__ testb(FieldOperand(rcx, Map::kBitFieldOffset),
Immediate(1 << Map::kIsCallable));
__ j(zero, &non_callable);
__ CmpInstanceType(rcx, JS_PROXY_TYPE);
__ j(not_equal, &non_function);
// 0. Prepare for tail call if necessary.
if (tail_call_mode == TailCallMode::kAllow) {
PrepareForTailCall(masm, rax, rbx, rcx, r8);
}
// 1. Runtime fallback for Proxy [[Call]].
__ PopReturnAddressTo(kScratchRegister);
__ Push(rdi);
__ PushReturnAddressFrom(kScratchRegister);
// Increase the arguments size to include the pushed function and the
// existing receiver on the stack.
__ addp(rax, Immediate(2));
// Tail-call to the runtime.
__ JumpToExternalReference(
ExternalReference(Runtime::kJSProxyCall, masm->isolate()));
// 2. Call to something else, which might have a [[Call]] internal method
(if
// not we raise an exception).
__ bind(&non_function);
// Overwrite the original receiver with the (original) target.
__ movp(args.GetReceiverOperand(), rdi);
// Let the "call_as_function_delegate" take care of the rest.
__ LoadNativeContextSlot(Context::CALL_AS_FUNCTION_DELEGATE_INDEX, rdi);
__ Jump(masm->isolate()->builtins()->CallFunction(
ConvertReceiverMode::kNotNullOrUndefined, tail_call_mode),
RelocInfo::CODE_TARGET);
// 3. Call to something that is not callable.
__ bind(&non_callable);
{
FrameScope scope(masm, StackFrame::INTERNAL);
__ Push(rdi);
__ CallRuntime(Runtime::kThrowCalledNonCallable);
}
}
It's pretty simple.
After several checks we can rich this lines:
// 1. Runtime fallback for Proxy [[Call]].
__ PopReturnAddressTo(kScratchRegister);
__ Push(rdi);
__ PushReturnAddressFrom(kScratchRegister);
// Increase the arguments size to include the pushed function and the
// existing receiver on the stack.
What? The pop function will return arg N - 1. Why this should be a return
address?
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