On Tue, 9 May 2000, Tigran Aivazian wrote:
> On Tue, 9 May 2000, Alan Modra wrote:
>
> > On Tue, 9 May 2000, Keith Owens wrote:
> >
> > > Why does kernel/Makefile set -fno-omit-frame-pointer for sched.c.
> > > AFAICT there are no comments in the code or the Makefile about this.
> >
> > Because switch_to in include/asm-i386/system.h breaks rather badly
> > otherwise.
>
> why not put this explanation in the Makefile next to it and send to Linus,
> please?
Because it's wrong :-( I should have checked exactly what gcc does before
firing off that email.
gcc can generate code that accesses parameters like prev->tss.esp
indexed from registers other than %esp, since switch_to is passed
prev, next, and last in registers. If this were not so, gcc might
access task_struct fields via %esp in the asm, which breaks as %esp is
altered by the pushes.
Hmm, actually I don't think there's anything to prohibit gcc from using
%esp anyway. Maybe I should rewrite switch_to to make sure of this.
Regards, Alan Modra
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