[gentoo-user] CFLAGS for both AMD64 and Intel?

[gentoo-user] CFLAGS for both AMD64 and Intel?

[Manuel McLure]

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Here's the situation. I have a system that's been running for many years
with an Athlon 5050e processor. The system is built with

CFLAGS="-march=k8-sse3 -O2 -pipe -msse3"
CPU_FLAGS_X86="3dnow 3dnowext mmx mmxext sse sse2 sse3"

I have the possibility of upgrading the system to a first-generation Intel
Core i5 which should give a nice speed boost, but of course the Intel chip
doesn't understand 3dnow or 3dnowext, so I'll have to do a system rebuild
before I switch out the motherboard/processor. It seems pretty obvious that
I have to take "3dnow 3dnowext" out of CPU_FLAGS_X86, but what CFLAGS would
be recommended for a system that will still run with the AMD processor but
won't fall over when I switch to the Intel processor? Once I have the Intel
in place I can rebuild with options more suited for that chip, but I want
to make sure I don't end up in a catch-22 situation.

-- 
Manuel A. McLure WW1FA <manuel@mclure.org> <http://www.mclure.org>
...for in Ulthar, according to an ancient and significant law,
no man may kill a cat.                       -- H.P. Lovecraft

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Re: [gentoo-user] CFLAGS for both AMD64 and Intel?

[Mike Gilbert]

On Sun, Dec 3, 2017 at 2:23 AM, Manuel McLure <manuel@mclure.org> wrote:
> Here's the situation. I have a system that's been running for many years
> with an Athlon 5050e processor. The system is built with
>
> CFLAGS="-march=k8-sse3 -O2 -pipe -msse3"
> CPU_FLAGS_X86="3dnow 3dnowext mmx mmxext sse sse2 sse3"
>
> I have the possibility of upgrading the system to a first-generation Intel
> Core i5 which should give a nice speed boost, but of course the Intel chip
> doesn't understand 3dnow or 3dnowext, so I'll have to do a system rebuild
> before I switch out the motherboard/processor. It seems pretty obvious that
> I have to take "3dnow 3dnowext" out of CPU_FLAGS_X86, but what CFLAGS would
> be recommended for a system that will still run with the AMD processor but
> won't fall over when I switch to the Intel processor? Once I have the Intel
> in place I can rebuild with options more suited for that chip, but I want to
> make sure I don't end up in a catch-22 situation.

I would go with just "-O2 -pipe" for maximum compatibility. Remove the
-march option altogether, and add it back once the system is running
on the Intel chip.

Re: [gentoo-user] CFLAGS for both AMD64 and Intel?

[Walter Dnes]

On Sat, Dec 02, 2017 at 11:23:10PM -0800, Manuel McLure wrote
> Here's the situation. I have a system that's been running for many years
> with an Athlon 5050e processor. The system is built with
> 
> CFLAGS="-march=k8-sse3 -O2 -pipe -msse3"
> CPU_FLAGS_X86="3dnow 3dnowext mmx mmxext sse sse2 sse3"
> 
> I have the possibility of upgrading the system to a first-generation
> Intel Core i5 which should give a nice speed boost, but of course the
> Intel chip doesn't understand 3dnow or 3dnowext, so I'll have to do
> a system rebuild before I switch out the motherboard/processor. It
> seems pretty obvious that I have to take "3dnow 3dnowext" out of
> CPU_FLAGS_X86, but what CFLAGS would be recommended for a system
> that will still run with the AMD processor but won't fall over when
> I switch to the Intel processor? Once I have the Intel in place I
> can rebuild with options more suited for that chip, but I want to
> make sure I don't end up in a catch-22 situation.

https://gcc.gnu.org/onlinedocs/gcc-6.4.0/gcc/x86-Options.html#x86-Options
lists what instruction sets gcc expects for any "-march=<whatever>"

  I would suggest rebuilding with...

CFLAGS="-march=nocona -O2 -pipe"
CPU_FLAGS_X86="mmx sse sse2 sse3"

  nocona was the first Intel cpu to support AMD64 instructions, and it's
the newest Intel that does not exceed your AMD.  The next Intel cpu, the
"core2" supports ssse3 which your AMD does not (count the "s"'s... very
carefully; sse3 != ssse3).

-- 
Walter Dnes <waltdnes@waltdnes.org>
I don't run "desktop environments"; I run useful applications

Re: [gentoo-user] CFLAGS for both AMD64 and Intel?

[Manuel McLure]

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On Sun, Dec 3, 2017 at 12:08 AM, Walter Dnes <waltdnes@waltdnes.org> wrote:

>
> https://gcc.gnu.org/onlinedocs/gcc-6.4.0/gcc/x86-Options.html#x86-Options
> lists what instruction sets gcc expects for any "-march=<whatever>"
>
>   I would suggest rebuilding with...
>
> CFLAGS="-march=nocona -O2 -pipe"
> CPU_FLAGS_X86="mmx sse sse2 sse3"
>
>   nocona was the first Intel cpu to support AMD64 instructions, and it's
> the newest Intel that does not exceed your AMD.  The next Intel cpu, the
> "core2" supports ssse3 which your AMD does not (count the "s"'s... very
> carefully; sse3 != ssse3).
>
>
Thanks! I have successfully rebuilt the system with "-march=nocona -O2
-pipe" (and switched to gcc 6.4.0/profile 17 while I was at it) and
everything seems to be running fine. Hopefully I can pick up a micro-ATX
LGA1156 motherboard for cheap and can do the processor upgrade soon.

-- 
Manuel A. McLure WW1FA <manuel@mclure.org> <http://www.mclure.org>
...for in Ulthar, according to an ancient and significant law,
no man may kill a cat.                       -- H.P. Lovecraft

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