>> No nothing crazy: >> CFLAGS="-Os -pipe -mtune=i686" > > i686? That's not amd64. You need something 64bit. Just use march=native > instead of mtune=i686.
Wait, what! I could swear I was reading march=native just a few minutes ago. mtune=i686 on amd64 just doesn't seem right, but it should compile. # echo | gcc -dM -E - -march=native /usr/libexec/gcc/x86_64-pc-linux-gnu/4.5.3/cc1 -E -quiet -v - -D_FORTIFY_SOURCE=2 -mtune=i686 -march=x86-64 gcc sets the correct march even if you set the wrong mtune. But as Michael says, just use march=native and you should be fine.
