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

[Daniel Jacobowitz <dan@debian.org>]

On Fri, Jul 27, 2001 at 02:48:20AM +0200, Thiemo Seufer wrote:
> Daniel Jacobowitz wrote:
> > _mcount was doing awful things to its caller's stack frame.
> 
> 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.

> [snip]
> > I think this is close enough; it only adds
> > one instruction.  Is this OK?
> 
> 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.

> > Do I need a "nop" after the subu?
> 
> It works here since it is expanded in an
> 
> 	addiu $29,$29,-40
> 
> which is executed in one cycle. The usual suspects for hazards
> to be NOPed are load/store insns and branches.

Ahh, OK.  I see.

> [snip]
> > +        "sw $31,20($29);" \
> >          "move $5,$31;" \
> >          "jal __mcount;" \
> >          "move $4,$1;" \
>             ^
> Some stylistic issue: In ".set noreorder" assembly it helps to
> indent the insns in a branch delay slot by one blank to avoid
> confusion about their non-sequential nature.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer