From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/9579 Path: news.gmane.org!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: long double on powerpc64 Date: Fri, 11 Mar 2016 14:04:35 +0100 Message-ID: <20160311130434.GE29662@port70.net> References: <20160311031636.GA3851@gordon.members.linode.com> <20160311041759.GU9349@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1457701540 18477 80.91.229.3 (11 Mar 2016 13:05:40 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 11 Mar 2016 13:05:40 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-9592-gllmg-musl=m.gmane.org@lists.openwall.com Fri Mar 11 14:05:36 2016 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1aeMl6-0001fN-AV for gllmg-musl@m.gmane.org; Fri, 11 Mar 2016 14:05:36 +0100 Original-Received: (qmail 26148 invoked by uid 550); 11 Mar 2016 13:04:47 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 26087 invoked from network); 11 Mar 2016 13:04:46 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Xref: news.gmane.org gmane.linux.lib.musl.general:9579 Archived-At: * Justin Cormack [2016-03-11 11:19:22 +0000]: > On 11 March 2016 at 04:17, Rich Felker wrote: > > On Thu, Mar 10, 2016 at 09:16:36PM -0600, Bobby Bingham wrote: > >> I've been working on a PPC64 port of musl lately. I've made some good > >> progress, and it's time to decide what to do about the long double type. > >> > >> The PPC64 ELFv2 ABI [1] calls for a 128 bit long double. It allows an > >> implementation to choose to use either IEEE quad, or IBM double double, > >> with IEEE quad being preferred. > >> > >> On the compiler side, it looks like things are a bit of a mess. > >> > >> Clang only supports IBM double double on PPC64, AFAICS, and therefore > >> won't work for us currently. > >> > >> GCC support is more complicated. It supports both 128 bit variants, as > >> well as supporting (and defaulting to) a 64 bit long double. To get a > >> 128 bit long double, you must build gcc with --with-long-double-128 or > >> pass -mlong-double-128, and even then you get IBM double double. To get > >> IEEE quad, you must additionally pass -mlong-double-128, though there > >> are whispers that the default may change in gcc 7 [2]. > >> > >> The final piece of bad news is that gcc can't successfully build musl on > >> PPC64 with IEEE quad long double. It chokes on even trivial code using > >> long double complex [3]. So only 64 bit long double is usable for now. > >> > >> The good news is that gcc's predefined macros are sufficient to detect > >> which long double variant is in use. My current thinking is that we can > >> support both 64 bit long and IEEE quad as two powerpc64 subarchs, even > >> if we can only implement 64 bit for now. Because it looks like the > >> future direction is for IEEE quad to become the default, I think that > >> should be the suffix-less subarch, and the 64 bit long double subarch > >> should have a -ld64 suffix or similar. > > > > My leaning would be to just go with ld64 if nobody has their act > > together for quad support, but let's see what people who want to use > > powerpc64 think about it. The only option that's not on the table is > > IBM double-double (because it's incompatible with musl's assumption of > > IEEE semantics; math-savvy people in the musl community already know > > this of course but I'm repeating it for the sake of possible > > newcomers). > > I think it would be a mistake to only support ld64, I think Bobby's approach > of two architectures is probably better, and maybe look to retire ld64 > eventually. > if long double is 64bit then the 128bit hw floats cannot be used with musl, because we don't want library support for __float128. note that the glibc position is that for __float128 support the minimum required gcc version has to change to gcc-7 because it is abi and libc needs complex support (which will not be in gcc-6 yet). https://gcc.gnu.org/ml/gcc-patches/2015-12/msg02222.html https://sourceware.org/ml/libc-alpha/2016-03/msg00193.html the problem with -ld64 suffix is that gcc-6 already has hardcoded dynamic linker names (i don't think we can change that now, before the gcc-6 release). so i'd leave the dynlinker name as is, use 64bit ld for now and rediscuss the issue when ieee128 long double works in gcc-7