From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 25067 invoked from network); 7 Aug 2020 15:22:49 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 7 Aug 2020 15:22:49 -0000 Received: (qmail 11690 invoked by uid 550); 7 Aug 2020 15:22:47 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 11669 invoked from network); 7 Aug 2020 15:22:46 -0000 Date: Fri, 7 Aug 2020 11:22:33 -0400 From: Rich Felker To: "Gamble, Bradley" , "musl@lists.openwall.com" Message-ID: <20200807152231.GA3265@brightrain.aerifal.cx> References: <1596795338498.26196@ncipher.com> <20200807104600.GB879655@port70.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200807104600.GB879655@port70.net> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] Support for PowerPC64 devices lacking AltiVec extentions On Fri, Aug 07, 2020 at 12:46:00PM +0200, Szabolcs Nagy wrote: > * Gamble, Bradley [2020-08-07 10:15:38 +0000]: > > I was initially encountering exceptions with longjmp()/setjmp() > > due to the use of lvx/stvx instructions to store and restore > > vector registers. These vector registers are AltiVec-specific and > > are not required for devices that do not have the AltiVec > > extentions, so simply removing them was enough to allow musl to > > function properly on e5500 devices. > > > > I initially considered whether a compile-time check in the > > configure script was possible, however I believe this has to be a > > run-time check to query whether the processor supports AltiVec > > extentions and to conditionally store/restore the registers if it > > does. I see that Arm targets use __hwcap for platform-specific > > functionality, and in hwcap.h for PowerPC64 there is a > > "PPC_FEATURE_HAS_ALTIVEC" definition. > > > > Would this be the correct way to detect this platform-specific behavior? > > __hwcap is the right check (e.g. used in the arm setjmp) > > it works if the missing altivec does not affect the call abi > of standard c functions (otherwise fixing setjmp/longjmp alone > will not help: a separate build of libc is needed targetting > your system's call abi). I believe we determined that lack of altivec does not affect ABI, at least not without use of 128-bit long double (which we don't do; musl's long double on powerpc64 is 64-bit). So based on what I remember of past discussions, I think it's fine to just add the branch on __hwcap. Rich