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Re: [patch] fix profiling in glibc for Linux/MIPS

Subject: Re: [patch] fix profiling in glibc for Linux/MIPS
From: Thiemo Seufer <>
Date: Fri, 27 Jul 2001 04:21:55 +0200
In-reply-to: <>
User-agent: Mutt/1.3.18i
Daniel Jacobowitz wrote:
> > Maybe I'm missing something, but both the old and the new code
> > add 8 byte more to sp than they subtracted before. How is this
> > supposed to work?
> It's supposed to do that, according to GCC.  Build something with -S
> -pg and look at it.

Well, I don't have a 32bit compiler here ATM, only a highly
experimental 64bit one. :-)  But I found in the GCC Code this
snippet in /config/mips.mips.h:

/* 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\tnoreorder\n");                                \
  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, "\tjal\t_mcount\n");                                   \
  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, "\t.set\treorder\n");                                  \
  fprintf (FILE, "\t.set\tat\n");                                       \

This means, 8 byte is indeed ok for 32bit targets, a 64bit one
would differ by 16 byte (and won't work with the code you've
changed anyway).

Nevertheless, IHMO it would be a good idea to support both targets.

> > Why do you save and restore $6, $7, seemingly without using them?
> Because they were already there; I was trying to keep this patch
> minimal.  My MIPS assembly knowledge, as I said, is a little scanty.

Hm, and I have too little knowledge about the profiler to give
helpful advice here.


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