Request for review (XXS): -XX:+TraceBytecodes does not work with -XX:+UseCompressedOops

[Coleen Phillimore]

Volker, Thank you for fixing this.  It looks good to me.   I can check 
it in this contribution, pending additional comments.

Coleen

On 12/16/2011 12:20 PM, Volker Simonis wrote:
> Hi,
>
> I've just realized that -XX:+TraceBytecodes does not work anymore if
> -XX:+UseCompressedOops is set.
>
> This is because TemplateInterpreterGenerator::trace_bytecode() uses
> 'r12' which holds the heap base for temporary saving the 'sp' before
> calling the Interpreter::trace_code() template:
>
>    __ mov(r12, rsp); // remember sp (can only use r12 if not using call_VM)
>    __ andptr(rsp, -16); // align stack as required by ABI
>    __ call(RuntimeAddress(Interpreter::trace_code(t->tos_in())));
>    __ mov(rsp, r12); // restore sp
>    __ reinit_heapbase();
>
> Notice that the comment explicitly mentions that 'r12' can only be
> used if 'call_VM' will not be used subsequently.
>
> But this is exactly what Interpreter::trace_code() does:
>
>
> address TemplateInterpreterGenerator::generate_trace_code(TosState state) {
> ...
>    __ call_VM(noreg,...
>
> void MacroAssembler::call_VM(Register oop_result,
> ...
>    call_VM_helper(oop_result, entry_point, 3, check_exceptions);
>
> void MacroAssembler::call_VM_helper(Register oop_result, address
> entry_point, int number_of_arguments, bool check_exceptions) {
> ...
>    call_VM_base(oop_result, noreg, rax, entry_point,
> number_of_arguments, check_exceptions);
>
> void MacroAssembler::call_VM_base(Register oop_result,
> ...
>    LP64_ONLY(if (UseCompressedOops) verify_heapbase("call_VM_base");)
>
>
> This finally leads to a call to 'verify_heapbase()' which will fail
> because 'r12' has been overwritten.
>
> The proposed fix is trivial: don't do the check if we are running with
> -XX:+TraceBytecodes:
>
> diff -r 86cbe939f0c7 src/cpu/x86/vm/assembler_x86.cpp
> --- a/src/cpu/x86/vm/assembler_x86.cpp  Mon Sep 19 12:18:46 2011 -0700
> +++ b/src/cpu/x86/vm/assembler_x86.cpp  Fri Dec 16 18:01:31 2011 +0100
> @@ -5967,7 +5967,7 @@
>     assert(number_of_arguments>= 0   , "cannot have negative number of
> arguments");
>     LP64_ONLY(assert(java_thread == r15_thread, "unexpected register"));
>   #ifdef ASSERT
> -  LP64_ONLY(if (UseCompressedOops) verify_heapbase("call_VM_base");)
> +  LP64_ONLY(if (UseCompressedOops&&  !TraceBytecodes)
> verify_heapbase("call_VM_base");)
>   #endif // ASSERT
>
>     assert(java_thread != oop_result  , "cannot use the same register
> for java_thread&  oop_result");
>
> For your convenience I've also attached the patch as a file to this message.
>
> Regards,
> Volker