On Sun, 13 Dec 1998, Andi Kleen wrote:
> In muc.lists.linux-kernel, you wrote:
> >
> >--YiEDa0DAkWCtVeE4
> >Content-Type: text/plain; charset=us-ascii
> >
> >Hello penguinoids,
> >
> >I have wrote a small patch against 2.1.131-ac9 which implements the
> >promised enhanced support for the new egcs/pgcc i386 target submodel
> >options such as -mpentium, -mpentiumpro, -march=pentium and
> >-march=pentiumpro.
>
> Suggested options for PPro/egcs 1.1:
>
> -O2 -march=pentiumpro -mpentiumpro -fno-gcse
>
> and remove the -malign-* options, because egcs does now a better job
> at that. -fno-gcse is needed to prevent code bloat and excessive spill
> code on x86 (the global CSE pass does not seem to be well tuned for
> register starved machines like the x86 yet). Also it is less risky, because
> GCSE does a lot of code movement, which might uncover locking bugs (this
> applies if you want a working kernel, if you want to uncover bugs it looks
> different ;)
>
> The problem is that gcc 2.7.2 does not understand these new options,
> so the Makefiles have to know which compiler version is being used.
> Now using a CONFIG_* option to select the kernel compiler is rather
> ugly, because the kernel makefile could just check for that itself. For
> that something like autoconf would be needed to determine the characteristics
> of the compilation host (not of the target, because the kernel might be
> cross compiled).
>
> Alternatives are cheap hacks like:
>
> Makefile.pre
>
> #if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8)
>
> ifdef CONFIG_M686
> ARCH_CFLAGS := -fno-gcse -mpentiumpro -march=pentiumpro -DCPU=686
> endif
>
> ... other processors
>
> #else /* GCC 2.7.x */
>
> ifdef CONFIG_M686
> # the bug of -fno-strength-reduce is fixed in 2.7.x minor releases,
> # so in theory we could test for that too.
> ARCH_CFLAGS := -fno-strength-reduce -m486 -DCPU=686 -malign-loops=2 ....
> endif
>
> #endif
>
>
> Real makefile:
>
> Makefile.cflags: arch/$(ARCH)/Makefile.pre
> $(MAKE) -f arch/$(ARCH)/Makefile Makefile.cflags
> include arch/$(ARCH)/Makefile.cflags
>
>
> -Andi
> >
>
> -
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