make.conf says -O3 but kernel compiles with -O2

Biker

My CFLAGS in make.conf contains "-O3". The full bootstrap process compiled with "-O3".

Still, the kernel compile insists on using "-O2".

'tis "working as designed"?

If so, why?

If not, how do I correct this?

Gus

dberkholz · Posted: Thu Jun 19, 2003 8:00 pm Post subject:

The kernel has its own set of CFLAGS.

DrkPlague · Tux's lil' helper Joined: 04 Jun 2003 Posts: 107

this is done for a reason. certain things such as the kernal and heavily used libs like glibc specify their own cflags to achieve what they consider to be optimal performance.

Also, i am pretty sure that specifying -O3 on kernel would prevent ANY debugging of programs, which is probably a bad idea. my advice is that the flags were put there for a reason and unless you are a kernel dev, don't touch them.
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qubex · Posted: Fri Jun 20, 2003 11:16 am Post subject:

Yeah, messing with kernel optimizations is bad, m'kay? If you try and optimize your kernel with -O3, you're bad, m'kay? :roll:

Seriously though, your kernel is the foundation of your system - why mess with it's stability? How's that stupid christian children's song go - the wise man built his house upon the mid optimized but quick and rock solid kernel, the foolish man built his house upon a highly optimized but memory-leaky and flaky kernel. Wait - maybe it doesn't go like that.. But then again, I'm not a christian (and I think you get the point.)

And -O3 *shouldn't* stop you from debugging, that's generally in the hands of -fomit-frame-pointer, but I could be wrong in this case.

M

DigitalP1mp · Posted: Fri Jun 20, 2003 1:16 pm Post subject: What's it all mean Bazil?

What's the -02 and the -03 all about. I'm at the point where I need to set my flags now and want to set them correctly. I have an AMD k-6-2 with a 400 mhZ processor.
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bsolar · Bodhisattva Joined: 12 Jan 2003 Posts: 2764

darket · n00b Joined: 19 Mar 2003 Posts: 43

the kernel might be using O2 instead of O3 because O3 increases the size of the binary, AFAIK. Or I'm completely off ;-)

For the K6-2: I would use -Os, because that uses all optimizations from O2 without a few to get a small binary - which appears to be better, because of the small on-die cache (L1 only) and the rather slow onboard-L2-Cache. Apart from that, look there:
http://www.freehackers.org/gentoo/gccflags/flag_gcc3.html

DrkPlague · Tux's lil' helper Joined: 04 Jun 2003 Posts: 107

yes -fomit-frame-pointer completely kills debugging, but -finline-functions (added by -O3) on the kernel and glibc REALLY reak havok on debugging since most function calls made to the kernel or glibc are near impossible to trace.

For those who don't understand what -O does, here it is strait from the horses mouth: