Passing gcc flags into custom kernel

brodo · 02-01-2006, 05:20 PM

How to inject "-Os -march=pentium3 -fomit-frame-pointer -pipe" gcc flags settings into kernel being custom compiled ?

Do I need to edit every Makefile in /usr/src/linux*** ?

I do it while compiling other software just by inserting these flags at CFLAGS declarations.

mdarby · 02-01-2006, 07:35 PM

Code:

export CFLAGS="-Os -march=pentium3 -fomit-frame-pointer -pipe"
export CXXFLAGS="-Os -march=pentium3 -fomit-frame-pointer -pipe"

brodo · 02-02-2006, 03:33 AM

Is it enough to run from bash these 2 export commands before running "make" ?

What if there will be another CFLAGS= declaration inside Makefile(s) processed later ? Will my hand declaraion be overwritten ?

mdarby · 02-02-2006, 05:52 AM

The above export commands will append what's already in the makefile, IIRC.
I have the statements in my ~/.bashrc with no ill effects...

KMcD · 02-02-2006, 07:59 AM

I have flags like the above in my .profile (and .bashrc) and they are over-ridden by the Makefile. You'll have to edit the Makefile I believe, at least that's how I changed it.

(On kernel 2.6.x there is the option for -Os, enabling that will do.)

cnd · 03-04-2012, 09:09 AM

I had to manually edit the 2 makefiles in this folder:-

/usr/src/redhat/BUILD/kernel-2.6.32/linux-2.6.32.x86_64/arch/x86

to get the thing to pick up those changes, prior to building like this:-

cd /usr/src/redhat/SPECS/;rpmbuild -bb --target `uname -m` kernel.spec

the3dfxdude · 03-04-2012, 09:32 AM

Set the following config options. It's better to do it this way, so you can keep a record of the config file. There's no reason to edit the Makefiles, or set CC on your own.

General setup -> Check "Optimize for size" (CONFIG_CC_OPTIMIZE_FOR_SIZE)
Processor type and features -> Processor family -> Check "Pentium-III/Celeron(Coppermine)/Xeon" (CONFIG_MPENTIUMIII)
Kernel hacking -> Uncheck "Compile the kernel with frame pointers" (CONFIG_FRAME_POINTER=n)

-pipe doesn't affect the quality of the compiled code.

narz · 03-05-2012, 03:17 AM

Quote:

Originally Posted by cnd

I had to manually edit the 2 makefiles in this folder:-

/usr/src/redhat/BUILD/kernel-2.6.32/linux-2.6.32.x86_64/arch/x86

to get the thing to pick up those changes, prior to building like this:-

cd /usr/src/redhat/SPECS/;rpmbuild -bb --target `uname -m` kernel.spec

You bumped a 6 year old Slackware thread to give Redhat advice?

cnd · 03-05-2012, 04:03 AM

@narz Why are you wasting everyones time with your stupid comment?

I obviously had my reasons, and you'd have to be pretty dim not to figure it out: This is the top google result for this issue, and the advice doesn't work for modern distros.

If you actually want to optimize your kernel for your running CPU, my response now tells people how to do that, which is to mod the -mtune=native parm into those 2 makefiles.

Do not reply. Go on. I dare you. Prove you're not a troll, and try not to reply.

55020 · 03-05-2012, 05:10 AM

Quote:

Originally Posted by cnd

This is the top google result for this issue, and the advice doesn't work for modern distros.

And, uh, what proportion of modern distros does your advice work for? the3dfxdude's advice works properly, for all distros, and the fact that the options are right there in the standard kernel menus for all to see is why nobody worries about this any more.

Allocation of stupidity is left as an exercise for the reader.

narz · 03-05-2012, 06:39 AM

Quote:

Originally Posted by cnd

@narz Why are you wasting everyones time with your stupid comment?

I obviously had my reasons, and you'd have to be pretty dim not to figure it out: This is the top google result for this issue, and the advice doesn't work for modern distros.

If you actually want to optimize your kernel for your running CPU, my response now tells people how to do that, which is to mod the -mtune=native parm into those 2 makefiles.

Do not reply. Go on. I dare you. Prove you're not a troll, and try not to reply.

Wow you're serious?? Like 55020 mentioned, the3dfxdude tells you exactly how to do all this on modern distros. You don't have to edit any makefiles. Try and relax.

unSpawn · 03-05-2012, 10:09 AM

Now now, there there. All quiet again... (Closed)