Hi,
On Sat, 2009-10-24 at 10:12 +0100, Richard Sandiford wrote:
> Thanks for the patch.
[...]
> > How about this patch, I think it does what you suggest.
> >
> > When we pass -pg -mmcount-raloc, the address of the return address
> > relative to sp is passed in $12 to _mcount. If the return address is
> > not saved, $12 will be zero. I think this will work as registers are
> > never saved with an offset of zero. $12 is a temporary register that is
> > not part of the ABI.
>
> Hmm, well, the suggestion was to pass a pointer rather than an offset,
> but both you and Wu Zhangjin seem to prefer the offset. Is there a
> reason for that? I suggested a pointer because
>
> (a) they're more C-like
> (b) they're just as quick and easy to compute
> (c) MIPS doesn't have indexed addresses (well, except for a few
> special cases) so the callee is going to have to compute the
> pointer at some stage anyway
>
Agree with you.
if not with -fno-omit-frame-pointer, we also need to calculate the frame
pointer, and then plus it with the offset. with pointer, we can get it
directly, but it may need a more instruction(lui..., addiu...) for
loading the pointer. of course, at last, the pointer will save more time
for us :-)
so, David, could you please use pointer instead? and then I will test it
asap(cloning the latest gcc currently). thanks!
> (It sounds from Wu Zhangjin's reply like he'd alread suggested the
> offset thing before I sent my message. If so, sorry for not using
> that earlier message as context.)
>
It doesn't matter, Seems at that time, you were not added in the CC
list, but added by David Daney later.
> > + if (TARGET_RALOC)
> > + {
> > + /* If TARGET_RALOC load $12 with the offset of the ra save
> > + location. */
> > + if (mips_raloc_in_delay_slot_p())
> > + emit_small_ra_offset = 1;
> > + else
> > + {
> > + if (Pmode == DImode)
> > + fprintf (file, "\tdli\t%s,%d\t\t# offset of ra\n", reg_names[12],
> > + cfun->machine->frame.ra_fp_offset);
> > + else
> > + fprintf (file, "\tli\t%s,%d\t\t# offset of ra\n", reg_names[12],
> > + cfun->machine->frame.ra_fp_offset);
> > + }
> > + }
>
> We shouldn't need to do the delay slot dance. With either the pointer
> ((D)LA) or offset ((D)LI) approach, the macro won't use $at, so we can
> insert the new code immediately before the jump, leaving the assembler
> to fill the delay slot. This is simpler and should mean that the delay
> slot gets filled more often in the multi-insn-macro cases.
>
> Looks good otherwise, but I'd be interested in other suggestions for
> the option name. I kept misreading "raloc" as a typo for "reloc".
>
The same misreading to me, what about -mmcount-ra-loc? add one "-", or
-mcount-ra-location?
BTW: Just made dynamic function tracer for MIPS support module tracing
with the help of -mlong-calls. after some more tests, I will send it as
-v5 revision later. hope the -v6 revision work with this new feature of
gcc from David Daney.
Regards,
Wu Zhangjin
