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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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