Re: loader breaks with -O2 optimizations

On 10/31/07, Kris Kennaway <kris_at_freebsd.org> wrote:
> Stephan F. Yaraghchi wrote:
> > After making world on a freshly installed 7.0-BETA1
> > the system does not boot anymore due to a broken loader:
> >
> >
> > FreeBSD/i386 bootstrap loader, Revision 1.1
> > (root_at_bigblue, Tue Oct 30 11:26:32 CET 2007)
> > Can't work out which disk we are booting from.
> > Guessed BIOS device 0xffffffff not found by probes defaulting to disk0:
> >
> > panic: free: guard1 fail_at_ 0x6ded4 from
> > /usr/src/sys/boot/i386/loader/../../common/module.c:959
> >
> > --> Press a key on the console to reboot <--
> >
> >
> > I found out that the following line in my make.conf causes
> > the problem:
> >
> > CFLAGS= -O2 -funroll-loops -pipe
> >
> >
> > After changing down to -O1 and making /usr/src/sys/boot again
> > the systems behaves properly at boot.
> >
> > Is this behavior intended?
>
> Maybe, what happens if you use just -O2 -pipe? -funroll-loops is not an
> appropriate thing to be using globally anyway, unless your intention is
> to randomly make some code slower.
>
> Kris
>

Hi Kris,

I tried all possible combinations of these switches -- only -O2 led to
the described
behaviour.

Anyway, it's very interesting to hear that adding these optimizations
to make.conf
is not recommended, even that -funroll-loops is possibly slowing down
certain code.

I'm sure many people use it since it's a common tuning tip found on the web.
I read about it in Dru Lavigne's "BSD Hacks" (O'Reilly)...


-- 
Stephan



www.deine-stimme-gegen-armut.de