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SubjectRe: glibc-2.1 upgrade headaches. Any ideas??
On Sun, Mar 07, 1999 at 02:09:17PM +1100, CaT wrote:
> I've been happily doing it for a while with -O2 optimisation and
> -march=pentiumpro and haven't had a single kernel crash.
>
> I'd use -O6 but I can't find any info on what the hell this does
> as far as optimisation goes.

The biggest you can go to currently is -O3, I believe. Anything beyond that
turns on the same flags.

>
> And is -fomit-frame-pointer a workaround for a bug in some implimentations
> of -O2 (I compiled X without it and it's working fine. Hasn't crashed) or
> is it something the kernel needs? And, what exactly does this do? I've read
> the manpage but what that has doesn't mean much to me. I wish there was
> info on not just what an optimisation flag does but also how it might effect
> performance and what sideeffects it might have. (this is probably real hard
> to do but it would be way useful. I don't mind long compile times as long
> as runtime performance is imporved)
From the gcc manual:

`-fomit-frame-pointer'
Don't keep the frame pointer in a register for functions that
don't need one. This avoids the instructions to save, set up and
restore frame pointers; it also makes an extra register available
in many functions. *It also makes debugging impossible on some
machines.*

This option is never turned on by default (on i386), so the kernel Makefile
turns it on.

Obviously, it should improve run-time performance, unless the gcc code
optimizer is so buggy that it generates faster code with less registers
available ;)

-- arvind

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