Re: loader breaks with -O2 optimizations
- From: Kris Kennaway <kris@xxxxxxxxxxx>
- Date: Wed, 31 Oct 2007 22:31:38 +0100
Stephan F. Yaraghchi wrote:
On 10/31/07, Kris Kennaway <kris@xxxxxxxxxxx> wrote:Stephan F. Yaraghchi wrote:After making world on a freshly installed 7.0-BETA1Maybe, what happens if you use just -O2 -pipe? -funroll-loops is not an
the system does not boot anymore due to a broken loader:
FreeBSD/i386 bootstrap loader, Revision 1.1
(root@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@ 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?
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.
Presumably you mean -O2 -funroll-loops, not -O2. Or are you saying the latter also breaks the loader?
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)...
Yes, unfortunately it's bogus advice. What does she say this option is good for?
Kris
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