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

[David Edelsohn <dje.gcc@gmail.com>]

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.

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