Re: [gentoo-user] Lowest common denominator compile

[Grant]

>>> Now I'm running into "trap invalid opcode" errors on the older
>>> systems.  Can I disable some of the newer CPU instruction sets on the
>>> master laptop when compiling to hopefully generate binaries that will
>>> work on the older systems?
>>
>>   Yes.  You need to find out CPU_FLAGS_X86 and "-march=" values the
>> machines have, and use that in make.conf.  Run the commands...
>>
>> cpuinfo2cpuflags-x86
>> gcc -c -Q -march=native --help=target | grep march=
>>
>> ...on the target machines.  This will tell you what "native" is and
>> what CPU_FLAGS_X86 values to use.
>>
>> https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/x86-Options.html#x86-Options
>> lists available "march=" options, and what instruction sets they support.
>> E.g. my old core2 desktop shows...
>>
>> [d531][waltdnes][~] cpuinfo2cpuflags-x86
>> CPU_FLAGS_X86="mmx mmxext sse sse2 sse3 ssse3"
>>
>> [d531][waltdnes][~] gcc -c -Q -march=native --help=target | grep march=
>>   -march=                               core2
>>
>>
>>   Unless the laptops are really old, you can probably get away with...
>> CFLAGS="-O2 march=core2 -mfpmath=sse -fopenmp -fomit-frame-pointer -pipe -fno-unwind-tables -fno-asynchronous-unwind-tables"
>>
>> booby trap 1) Unless all machines are Intel "Atom" family, do *NOT* use
>> a "march=" that implements the "movbe" instruction.
>>
>> booby trap 2) If you throw in any AMD-based machines proceed with care.
>>
>>   Can you post the output of...
>> gcc -c -Q -march=native --help=target | grep march=
>> ...for all the target machines?
>
>
> Let's see how -mtune=native goes and resort to the above if necessary.
> It doesn't look too bad though.


emerge -e world has finished and pushed and -mtune=native seems to
have solved the issue for now.

- Grant