Date: Mon, 12 Jun 2017 09:28:52 -0400 From: David Edelsohn <dje.gcc@...il.com> To: musl@...ts.openwall.com Subject: Re: [PATCH] s390x: Add single instruction math functions On Mon, Jun 12, 2017 at 5:03 AM, Szabolcs Nagy <nsz@...t70.net> wrote: > * David Edelsohn <dje.gcc@...il.com> [2017-06-11 22:46:09 -0400]: > >> On Sun, Jun 11, 2017 at 6:19 AM, Szabolcs Nagy <nsz@...t70.net> 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 >> >> 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. 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. Thanks, David
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