From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Thu, 17 Aug 2017 09:15:47 +0200 (CEST) Received: from localhost.localdomain ([127.0.0.1]:58514 "EHLO linux-mips.org" rhost-flags-OK-OK-OK-FAIL) by eddie.linux-mips.org with ESMTP id S23992241AbdHQHPhm80Ne (ORCPT ); Thu, 17 Aug 2017 09:15:37 +0200 Received: from h7.dl5rb.org.uk (localhost [127.0.0.1]) by h7.dl5rb.org.uk (8.15.2/8.14.8) with ESMTP id v7H7FZ49000607; Thu, 17 Aug 2017 09:15:35 +0200 Received: (from ralf@localhost) by h7.dl5rb.org.uk (8.15.2/8.15.2/Submit) id v7H7FYAf000606; Thu, 17 Aug 2017 09:15:34 +0200 Date: Thu, 17 Aug 2017 09:15:34 +0200 From: Ralf Baechle To: Thomas Petazzoni Cc: Matthew Fortune , linux-mips@linux-mips.org, Waldemar Brodkorb Subject: Re: undefined reference to `__multi3' when building with gcc 7.x Message-ID: <20170817071534.GH13257@linux-mips.org> References: <20170803225547.6caa602b@windsurf.lan> <20170804000556.GC30597@linux-mips.org> <20170804151920.GA11317@linux-mips.org> <20170804174151.2eea9af3@windsurf.lan> <20170804222500.GA11675@linux-mips.org> <20170805135649.152b0739@windsurf> <20170807083448.GA20713@linux-mips.org> <20170813224602.25043e8a@windsurf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170813224602.25043e8a@windsurf> User-Agent: Mutt/1.8.3 (2017-05-23) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 59605 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Sun, Aug 13, 2017 at 10:46:02PM +0200, Thomas Petazzoni wrote: > Date: Sun, 13 Aug 2017 22:46:02 +0200 > From: Thomas Petazzoni > To: Ralf Baechle > Cc: Matthew Fortune , > linux-mips@linux-mips.org, Waldemar Brodkorb > Subject: Re: undefined reference to `__multi3' when building with gcc 7.x > Content-Type: text/plain; charset=US-ASCII > > Hello, > > On Mon, 7 Aug 2017 10:34:48 +0200, Ralf Baechle wrote: > > > > > Chances are it's something specific to MIPS64 R6. Before trying your > > > > config file I also tried a number of other defconfigs and all built > > > > well. > > > > > > > > Here's a test case which generates a reference to __multi3: > > > > > > > > unsigned long func(unsigned long a, unsigned long b) > > > > { > > > > return a > (~0UL) / b; > > > > } > > > > > > > > GCC rearanges above statement to: > > > > > > > > return (unsigned __int128)a * (unsigned __int128) b > 0xffffffff; > > > > > > And this is normal/expected ? > > > > Without consideration of performance, It's certainly is valid code. And > > with that I can't drop the issue as a GCC code generation bug. > > > > However it seems GCC itself doesn't seem to have a __multi3 in its > > libgcc2 - which indeed would be a GCC issue - at least none I was easily > > able to find with grep so I'm adding Matthew Fortune to cc in the hope he > > can shed some light on this. > > Indeed, I don't see __multi3 implemented in libgcc in the source code, > but it's probably because it's tricky to see its implementation, > as it really is there: > > $ ./bin/mips64el-linux-readelf -a ./mips64el-buildroot-linux-uclibc/sysroot/lib/libgcc_s.so.1 | grep multi3 > 1747: 00011700 100 FUNC GLOBAL DEFAULT 11 __multi3@@GCC_3.0 > 5511: 00011700 100 FUNC GLOBAL DEFAULT 11 __multi3 > 000435e4 -32236(gp) 00011700 00011700 FUNC 11 __multi3 > > Objdump says: > > 00011700 <__multi3>: > 11700: 0006103e dsrl32 v0,a2,0x0 > 11704: 7c89f803 dext a5,a0,0x0,0x20 > 11708: 0004403e dsrl32 a4,a0,0x0 > 1170c: 7ccaf803 dext a6,a2,0x0,0x20 > 11710: 012a589c dmul a7,a5,a6 > 11714: 010a509c dmul a6,a4,a6 > 11718: 0122489c dmul a5,a5,v0 > 1171c: 0102409c dmul a4,a4,v0 > 11720: 012a482d daddu a5,a5,a6 > 11724: 000b103e dsrl32 v0,a7,0x0 > 11728: 0049102d daddu v0,v0,a5 > 1172c: 184a0003 bgeuc v0,a6,1173c <.L2> > 11730: 24090001 li a5,1 > 11734: 0009483c dsll32 a5,a5,0x0 > 11738: 0109402d daddu a4,a4,a5 I happened to have a GCC build dir around so I greped for __multi3 and found it hiding in muldi3.o. Maybe that'obvious for those in the know, not me :) Also that .o file contained MIPS III code and I was able to get GCC to emit a reference to __multi3 for MIPS III or MIPS64R1 targets, so version of __multi3 even seems unused. Ralf