Gentoo compile flags

This page gives an introduction to Gentoo compile flags.

About compile flags in Gentoo

One strength of Gentoo is the ability to use global flags for code optimizing. This is done through the file /etc/make.conf (man page). Since the Pentium Mobile (Centrino) used in some Thinkpads supports the mmx and sse extensions of the insturuction set, using compile flags can speedup programs quite a bit. To use optimized code, you have to adjust the USE (Gentoo Handbook) variable, which contains the libraries and extensions you want to use and the CFLAGS variable, which contains compiler flags, that portage passes along to gcc.

If you want to set specific flags for only one package, you can also use the file /etc/portage/package.use instead of the USE variable in make.conf.

Which flags to use

Gentoo has a separate wiki page for deciding which CFLAGS are right for you. Use your model's page here at ThinkWiki to figure out your processor family, then look it up on that page for the proper CFLAGS. That page may assume that you're using GCC version 4.2, but this is the case on all reasonably modern systems.

Additionally, it may help to include some of the following USE flags:

USE="mmx sse sse2 ssse3"

Run the command "cat /proc/cpuinfo" and look through the "flags" section to see which your CPU supports; only include those in your global USE flag.

Example files

These are the make.conf and package.use files used for a T40P:

make.conf

USE="X mmx mmx2 sse sse2 qt kde -gpm -gtk -gtk2 -gnome -arts -alsa -cups -java -esd -v4l -v4l1 -samba -ipv6 -directfb -lirc -svga"
CFLAGS="-O2 -march=pentium4 -pipe -fomit-frame-pointer"
CHOST="i686-pc-linux-gnu"
CXXFLAGS="${CFLAGS}"
MAKEOPTS="-j2"

package.use

sys-libs/glibc userlocales
app-laptop/tpb xosd
media-video/mplayer dvd xanim divx4linux network xvid live
media-libs/xine-lib dvd

This is the make.conf files used for a 64-bit T61 (with Intel X3100 graphics):

make.conf

CFLAGS="-march=nocona -O2 -pipe"
CXXFLAGS="${CFLAGS}"
MAKEOPTS="-j5"
CHOST="x86_64-pc-linux-gnu"
VIDEO_CARDS="vesa vga i810"
ALSA_CARDS="hda-intel" 
INPUT_DEVICES="keyboard mouse evdev synaptics"

Other portage features

There are lots of other great features in portage (the Gentoo package managing system). If you want to use Gentoo, you should read the docs on gentoo.org and the man pages of portage and make.conf.

Gentoo compile flags