On Sun, Mar 22, 2015 at 10:03 AM, Mike Gilbert <flop...@gentoo.org> wrote: > On Sat, Mar 21, 2015 at 3:52 PM, Fernando Rodriguez > <frodriguez.develo...@outlook.com> wrote: >> On Saturday, March 21, 2015 8:46:10 AM Mike Gilbert wrote: >>> On Thu, Mar 19, 2015 at 12:20 AM, Walter Dnes <waltd...@waltdnes.org> wrote: >>> > CFLAGS="-O2 -march=atom -mno-cx16 -msahf -mmovbe -mno-aes -mno-pclmul - >> mno-popcnt -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi -mno-bmi2 - >> mno-tbm -mno-avx -mno-avx2 -mno-sse4.2 -mno-sse4.1 -mno-lzcnt -mno-rtm -mno- >> hle -mno-rdrnd -mno-f16c -mno-fsgsbase -mno-rdseed -mno-prfchw -mno-adx >> -mfxsr >> -mno-xsave -mno-xsaveopt --param l1-cache-size=24 --param l1-cache-line- >> size=64 --param l2-cache-size=512 -mtune=atom -fstack-protector -mfpmath=sse >> - >> fomit-frame-pointer -pipe -fno-unwind-tables -fno-asynchronous-unwind-tables" >>> > >>> > Is that correct (assuming that's my output)? >>> > >>> >>> I should warn you against including all of those -mno-xxx flags. This >>> has been known to break the build process for packages like chromium, >>> which always wants to build with SSE4 support and toggles it off at >>> runtime. Passing -mno-sse4.1 causes a build failure as it tries to use >>> macros that are not defined. >>> >> >> Isn't it possible that removing it for all packages would cause a more subtle >> problem with another faulty ebuild (like a program crashing due to an illegal >> instruction)? > > Passing -march=atom should be sufficient to ensure that you don't get > any illegal instructions. The -mno-XXX flags are redundant, and MOSTLY > harmless. > > In the case of chromium, the build system adds -msse4.1 for specific > files (just the ones using SSE4.1 instructons). When you have > -mno-sse4.1, this takes precedence and the build fails.
To put it another way: back in the day before gcc -march=native, nobody would have told you to put a bunch of -mno-xxx flags in your global CFLAGS. They would have told you to find the -march setting most appropriate for your processor.
