> 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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