Re: [gentoo-user] Will a 64-bit-no-multilib machine cross-compile 32-bit code?

[Mike Gilbert <floppym@gentoo.org>]

On Sat, Mar 21, 2015 at 3:52 PM, Fernando Rodriguez
<frodriguez.developer@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 <waltdnes@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.