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Message-ID: <CAGWvnym2NQCpFrWvBEk=bwx18CSuh8RbQdmoGWhFXAgXfD7_nQ@mail.gmail.com>
Date: Sun, 18 Jun 2017 13:12:15 -0400
From: David Edelsohn <dje.gcc@...il.com>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] s390x: Add single instruction math functions
How can we move forward with this patch?
I would prefer to avoid the __ARCH__ complexity until there is a clear
user requirement.
Thanks, David
On Wed, Jun 14, 2017 at 7:44 PM, Rich Felker <dalias@...c.org> wrote:
> On Mon, Jun 12, 2017 at 09:28:52AM -0400, David Edelsohn wrote:
>> >> The following IBM table of supported and tested systems
>> >>
>> >> https://www-03.ibm.com/systems/z/os/linux/resources/testedplatforms.html
>> >>
>> >> shows that RHEL 7 and SLES 12 require at least z196, and Ubuntu 16.04
>> >> requires at least zEC12.
>> >>
>> >> I can't find any official hardware requirements description for Alpine
>> >> Linux. I tend to doubt that user would run it on older hardware,
>> >> especially hardware no longer supported by other, modern Linux
>> >> distributions.
>> >>
>> >> Building musl libc on older hardware is a nice accomplishment, but
>> >> investing effort and complexity to maintain support probably isn't
>> >> useful to any musl libc user and probably isn't a productive use of
>> >> developer resources.
>> >>
>> >> I will continue to inquire if there is a simple technique to accomplish this.
>>
>> Apparently GCC 7.1 added architecture macros.
>>
>> As Tuan referenced, Alpine Linux also requires z196 as the minimum
>> architecture level. I believe that it would be better for s390-musl
>> to default to z196 ISA than musl to require GCC 7.1.
>
> I agree we shouldn't "require GCC 7.1", but using the macros does not
> imply such a requirement. For example:
>
> #if __ARCH__ >= 10
>
> would only use the asm on z196+ (if I got the number right) with GCC
> 7.1+ (no asm on older compilers), whereas:
>
> #if __ARCH__ >= 10 || !defined(__ARCH__)
>
> would use the asm on z196+ or on compilers too old to provide __ARCH__
> (and building for a more minimal baseline ISA would not be supported
> on such compilers unless you manually add -D__ARCH__=5 or whatever to
> CFLAGS).
>
> I'm fine with waiting to add those pp conditionals until if/when
> someone actually wants to use the lower baseline ISA, if you don't
> want to do it now. I am hesitant to add new ISA-forcing logic to
> configure, though (see the other reply on that). Would it be bad to
> have the build fail with low default -march? If so, maybe the
> configure logic could check for !defined(__ARCH__) and then do a
> compile test to define __ARCH__ on its own, and we could use the above
> logic?
>
> Rich
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