Re: [PATCH] s390x: Add single instruction math functions

[Szabolcs Nagy <nsz@port70.net>]

* David Edelsohn <dje.gcc@gmail.com> [2017-06-11 22:46:09 -0400]:

> On Sun, Jun 11, 2017 at 6:19 AM, Szabolcs Nagy <nsz@port70.net> wrote:
> > * Rich Felker <dalias@libc.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
> 
> I have asked the IBM toolchain team how to distinguish the
> architecture level at compile time, or at least distinguish support
> for the FP rounding instruction.
> 
> Are you actually running s390x musl on a system earlier than z196
> architecture level?  The public IBM LinuxONE Cloud is running on a z13
> system, many generations newer than even z196.
> 

no, i only have a cross compiler, but since the toolchain build script
uses default settings i get z900 arch, if that's not good then gcc
config default should be fixed for musl.

> 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.
> 
> Thanks, David