Re: [gentoo-user] CFLAGs for kernel compilation

[Andrew Savchenko]

On Thu, 30 Apr 2015 20:11:52 +0200 Volker Armin Hemmann wrote:
> Am 30.04.2015 um 19:45 schrieb Andrew Savchenko:
> > Hi,
> >
> > On Thu, 30 Apr 2015 18:26:22 +0200 Volker Armin Hemmann wrote:
> >> That simple. The kernel is too important and the people programming it
> >> know what they are doing. Don't set anything. It is retarded.
> >>> - I don't like invoking 'CFLAGS="-O2 -march=foo"make'
> >>> - I don't want to set CFLAGS as a persistent environment variable.
> >>> - I don't want to modify the kernel Makefile
> >>>
> >>> Does it actually make sense to set an optimization level and -march?
> >> no
> > While I completely agree with you that kernel CFLAGS should not be
> > randomly tampered with, I can't agree that -march itself is useless.
> > Tests and results are available here:
> > https://github.com/graysky2/kernel_gcc_patch
> >
> > Optimization is a very powerful tool if taken with care. Of course
> > it may lead to a disastrous result if mindlessly used.
> >
> > Best regards,
> > Andrew Savchenko
>
> if your mail client or browser is miscompiled, it is crashy, but worst
> case, a bunch of emails or bookmarks are lost.
>
> If the kernel fucks up, it might write across partition boundaries and
> destroy ALL your data. Or writes garbage instead of data.
>
> Don't f* with the kernel.

That's why we have tests. Follow the link above. As for a personal
experience: we have kernels with this patch and gcc native
optimization in production for several years. Results are fine
(no kernel related issues).

In order not to crash kernel, do not add -ffast-math there. You
need to have some understanding before touching such stuff.

Best regards,
Andrew Savchenko