Date: Wed, 14 Jun 2017 19:44:26 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH] s390x: Add single instruction math functions 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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