Hi,
I have been working on the MIPS port of v8, and I have a little
question.
I am working with the JavaScript shell, and follow the ARM port code.
My shell can compile any arithmetic operation an return with success.
I am working on calls to JS functions. For now I just compile a script
with a dummy function returning one of its arguments:
myfunc(p1, p2) { return p2; }
myfunc(2,5);
I have an issue with v8 not jumping to the right place in the
CodeGenerator::VisitCall(Call* node) function.
The VisitCall code layout is as follow:
Handle<Code> stub = ComputeCallInitialize(arg_count, in_loop);
[...]
frame_->CallCodeObject(stub, RelocInfo::CODE_TARGET_CONTEXT, arg_count
+ 1);
[...]
I generate and copy correctly some code through the
ComputeCallInitialize call:
At the stub location_ property address I can find a Code object, with
my actual code beginning at a (Code::kHeaderSize - kHeapObjectTag)
offset.
Through CallCodeObject I end up on a call to MacroAssembler::Call
(Handle<Code> code, RelocInfo::Mode rmod,[...]).
void MacroAssembler::Call(Handle<Code> code, RelocInfo::Mode rmode,
Condition cond, Register r1, const Operand&
r2) {
ASSERT(RelocInfo::IsCodeTarget(rmode));
Call(reinterpret_cast<intptr_t>(code.location(), rmode, cond, r1,
r2);
}
This does not work for me and I can't understand how it does on ARM.
The code is at *(code.location()) + code_offset; and here it seems to
me we will end up jumping to code.location() instead.
When I look at the ARM MacroAssembler::Call(intptr_t target,
RelocInfo::Mode rmode, [...]) I see
mov ra, pc
mov pc, target => mov pc, code.location()
Maybe the solution lies in the commentary saying "Emit a ldr<cond> pc,
[pc + offset of target in constant pool].", but I can't undersand
where we do with a constant pool offset.
I think the intptr_t type target also indicates that target is a
pointer to the actual address, but I still can't see when we get the
actual code address to jump to.
Debugging gives me the following:
stub.location_ = 0x6e34e8
*stub = 0x2ce79a21 and the generated code is thus at 0x2ce79a40 (I
can read it in memory)
With the ARM version of the code it seems I jump to 0x6e34e8 and I
meet an illegal instruction.
By patching the code to go to *(code.location()) + code_offset I reach
the generated code (generated by CallIC::Generate through the
ComputeCallInitialize call).
Thanks for your help.
Alexandre
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