Re: [gentoo-user] Lowest common denominator compile

[Grant <emailgrant@gmail.com>]

>> 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.

Thanks,
Grant