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Date: Sun, 11 Jun 2017 17:45:37 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] s390x: Add single instruction math functions
On Sun, Jun 11, 2017 at 06:45:00PM +0200, Szabolcs Nagy wrote:
> * Rich Felker <dalias@...c.org> [2017-06-11 11:04:38 -0400]:
> > On Sun, Jun 11, 2017 at 12:19:55PM +0200, Szabolcs Nagy wrote:
> > > * Rich Felker <dalias@...c.org> [2017-06-10 22:20:44 -0400]:
> > > > On Sat, Jun 10, 2017 at 05:48:05PM -0400, David Edelsohn wrote:
> > > > > When I worked with Bobby Bingham to create the s390x port of Musl, I
> > > > > said that he could assume newer processors. Also, I don't believe
> > > > > that LLVM supports the earlier processors. I believe that he assumed
> > > > > some more recent instructions in other parts of the code.
> > > >
> > > > That seems doubtful; the amount of asm in musl is minimal and unlikely
> > > > to benefit from later ISA levels; all the instructions I see look like
> > > > very basic stuff that would always have been available.
> > > >
> > > > Now, what likely is accurate is your claim that nobody is using musl
> > > > on lower ISA levels, so maybe it doesn't matter.
> > >
> > > well i am using s390x musl with lower isa level for compile tests
> > >
> > > and it seems gas rejects unrecognized opcodes so the new inline
> > > asm does not compile for me.
> > >
> > > i think either musl configure should make sure the cc targets
> > > the right isa level or the code should handle it with ifdefs
> >
> > Do you know the right predefined macros to check the ISA level? David,
> > any objection to including the #if/#ifdef since at least someone seems
> > to want ability to build for minimum ISA level?
> >
>
> i see no diff between
>
> s390x-linux-musl-gcc -E -dM -
>
> and
>
> s390x-linux-musl-gcc -E -dM -march=z196 -
>
> so it's not possible to tell at compile time, but the asm
> is different so configure can detect it:
>
> $ s390x-linux-musl-gcc -S -xc /dev/null -o -
> .machinemode zarch
> .machine "z900"
> .ident "GCC: (GNU) 6.3.0"
> .section .note.GNU-stack,"",@progbits
> $ s390x-linux-musl-gcc -S -xc /dev/null -o - -march=z196
> .machinemode zarch
> .machine "z196"
> .ident "GCC: (GNU) 6.3.0"
> .section .note.GNU-stack,"",@progbits
That's... bleh. This should probably be fixed on the gcc side...
Rich
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