Re: Mips profiling

["Kris Warkentin" <kewarken at qnx dot com>]

Replying to myself with some more observations - it seems that profiled code
on mips when compiled with optimization level -O2 is invalid.  I've verified
it on QNX6 (2.95.3) and Irix (3.0.1).  As near as I can tell from my
preliminary analysis, somewhere along the line the ra register is getting
clobbered and we wind up executing instructions off in the wild blue yonder.

cheers,

Kris
----- Original Message -----
From: "Kris Warkentin" <kewarken@qnx.com>
To: <gcc@gcc.gnu.org>
Sent: Thursday, March 21, 2002 10:29 AM
Subject: Mips profiling


> I've been looking at the following chunk of code from
gcc/config/mips/mips.h
> and something is puzzling me.  The bit about 'mcount pops 2 words from
> stack' seems wrong.  I believe the first four arguments to a function in
> mips will be passed in registers and the stack won't be involved.  If I
read
> this correctly, we're leaking 8 bytes of stack memory per function call.
> The other question would be 'why don't we have something in the branch
delay
> slot of jal _mcount'?  Wouldn't this cause problems depending on what this
> code was inserted before?  Or did removing the '.set noreorder' which used
> to be in front of '.set noat' take care of this?
>
> cheers,
>
> Kris
>
> /* Output assembler code to FILE to increment profiler label # LABELNO
>    for profiling a function entry.  */
>
> #define FUNCTION_PROFILER(FILE, LABELNO)    \
> {         \
>   if (TARGET_MIPS16)       \
>     sorry ("mips16 function profiling");    \
>   fprintf (FILE, "\t.set\tnoat\n");     \
>   fprintf (FILE, "\tmove\t%s,%s\t\t# save current return address\n", \
>     reg_names[GP_REG_FIRST + 1], reg_names[GP_REG_FIRST + 31]); \
>   fprintf (FILE,       \
>     "\t%s\t%s,%s,%d\t\t# _mcount pops 2 words from  stack\n", \
>     TARGET_64BIT ? "dsubu" : "subu",    \
>     reg_names[STACK_POINTER_REGNUM],    \
>     reg_names[STACK_POINTER_REGNUM],    \
>     Pmode == DImode ? 16 : 8);     \
>   fprintf (FILE, "\tjal\t_mcount\n");                                   \
>   fprintf (FILE, "\t.set\tat\n");     \
> }
>
>
>
>