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    SubjectRe: [PATCH] Support new egcs/pgcc -mpentium(pro) options
    On Sun, 13 Dec 1998, Andi Kleen wrote:

    > Suggested options for PPro/egcs 1.1:
    >
    > -O2 -march=pentiumpro -mpentiumpro -fno-gcse

    Euhm, read the docs. -march=pentiumpro IMPLIES -mpentiumpro, that is why
    I haven't put that in as well. I did not know about the no-gcse thing,
    however.

    > 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 ;)

    Besides the -fno-gcse, you should really have a closer look at my patch.
    These -malign/-m options are only used if enabled in the config and
    should default to off...

    > 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.

    ...to circumvent this.

    > 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 would prevent the user from deciding for himself IF he wants to use
    these new options.

    > 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).

    Surely, the thing that matters is the compiling host. If the host does
    not support a target feature, we can't have it.

    > Alternatives are cheap hacks like:
    >
    > Makefile.pre
    >
    > #if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8)

    Am I missing something here? How can a Makefile know about the compiler?

    I am just wondering if this construct can be used to pass the compiler
    version to the *config scripts which then could disable the new -m
    directives in turn.

    > 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.

    I don't care for 2.6 and older gcc any more. 2.7.2.x are stable.

    --
    Matthias Andree
    --- How to obtain PGP public key
    <mandree@dosis.uni-dortmund.de> <<< /finger/ this
    <m_andree@line.org> <<< mail, subject "SEND PGP-PUBLIC-KEY"


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