From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757565AbcBDLDr (ORCPT ); Thu, 4 Feb 2016 06:03:47 -0500 Received: from mx2.suse.de ([195.135.220.15]:55997 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965729AbcBDLC2 (ORCPT ); Thu, 4 Feb 2016 06:02:28 -0500 Date: Thu, 4 Feb 2016 12:02:24 +0100 From: Petr Mladek To: AKASHI Takahiro Cc: Torsten Duwe , Jiri Kosina , Steven Rostedt , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH v6 1/9] ppc64 (le): prepare for -mprofile-kernel Message-ID: <20160204110224.GD731@pathway.suse.cz> References: <20160125170459.14DB7692CE@newverein.lst.de> <20160125170723.D2CCE692CE@newverein.lst.de> <56B1AAE5.10500@linaro.org> <20160203112449.GA27247@lst.de> <56B31A7C.2050803@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56B31A7C.2050803@linaro.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2016-02-04 18:31:40, AKASHI Takahiro wrote: > Jiri, Torsten > > Thank you for your explanation. > > On 02/03/2016 08:24 PM, Torsten Duwe wrote: > >On Wed, Feb 03, 2016 at 09:55:11AM +0100, Jiri Kosina wrote: > >>On Wed, 3 Feb 2016, AKASHI Takahiro wrote: > >>>those efforts, we are proposing[1] a new *generic* gcc option, -fprolog-add=N. > >>>This option will insert N nop instructions at the beginning of each function. > > > >>The interesting part of the story with ppc64 is that you indeed want to > >>create the callsite before the *most* of the prologue, but not really :) > > > >I was silently assuming that GCC would do this right on ppc64le; add the NOPs > >right after the TOC load. Or after TOC load and LR save? ... > > On arm/arm64, link register must be saved before any function call. So anyhow > we will have to add something, 3 instructions at the minimum, like: > save lr > branch _mcount > restore lr > > ... > > ... So, it is similar to PPC that has to handle LR as well. > >>The part of the prologue where TOC pointer is saved needs to happen before > >>the fentry/profiling call. > > > >Yes, any call, to any profiler/tracer/live patcher is potentially global > >and needs the _new_ TOC value. The code below is generated for PPC64LE with -mprofile-kernel using: $> gcc --version gcc (SUSE Linux) 6.0.0 20160121 (experimental) [trunk revision 232670] Copyright (C) 2016 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 0000000000000050 : 50: 00 00 4c 3c addis r2,r12,0 50: R_PPC64_REL16_HA .TOC. 54: 00 00 42 38 addi r2,r2,0 54: R_PPC64_REL16_LO .TOC.+0x4 58: a6 02 08 7c mflr r0 5c: 01 00 00 48 bl 5c 5c: R_PPC64_REL24 _mcount 60: a6 02 08 7c mflr r0 64: 10 00 01 f8 std r0,16(r1) 68: a1 ff 21 f8 stdu r1,-96(r1) 6c: 00 00 22 3d addis r9,r2,0 6c: R_PPC64_TOC16_HA .toc 70: 00 00 82 3c addis r4,r2,0 70: R_PPC64_TOC16_HA .rodata.str1.8 74: 00 00 29 e9 ld r9,0(r9) 74: R_PPC64_TOC16_LO_DS .toc 78: 00 00 84 38 addi r4,r4,0 78: R_PPC64_TOC16_LO .rodata.str1.8 7c: 00 00 a9 e8 ld r5,0(r9) 80: 01 00 00 48 bl 80 80: R_PPC64_REL24 seq_printf 84: 00 00 00 60 nop 88: 00 00 60 38 li r3,0 8c: 60 00 21 38 addi r1,r1,96 90: 10 00 01 e8 ld r0,16(r1) 94: a6 03 08 7c mtlr r0 98: 20 00 80 4e blr And the same function compiled using: $> gcc --version gcc (SUSE Linux) 4.8.5 Copyright (C) 2015 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 0000000000000050 : 50: 00 00 4c 3c addis r2,r12,0 50: R_PPC64_REL16_HA .TOC. 54: 00 00 42 38 addi r2,r2,0 54: R_PPC64_REL16_LO .TOC.+0x4 58: a6 02 08 7c mflr r0 5c: 10 00 01 f8 std r0,16(r1) 60: 01 00 00 48 bl 60 60: R_PPC64_REL24 _mcount 64: a6 02 08 7c mflr r0 68: 10 00 01 f8 std r0,16(r1) 6c: a1 ff 21 f8 stdu r1,-96(r1) 70: 00 00 42 3d addis r10,r2,0 70: R_PPC64_TOC16_HA .toc 74: 00 00 82 3c addis r4,r2,0 74: R_PPC64_TOC16_HA .rodata.str1.8 78: 00 00 2a e9 ld r9,0(r10) 78: R_PPC64_TOC16_LO_DS .toc 7c: 00 00 84 38 addi r4,r4,0 7c: R_PPC64_TOC16_LO .rodata.str1.8 80: 00 00 a9 e8 ld r5,0(r9) 84: 01 00 00 48 bl 84 84: R_PPC64_REL24 seq_printf 88: 00 00 00 60 nop 8c: 00 00 60 38 li r3,0 90: 60 00 21 38 addi r1,r1,96 94: 10 00 01 e8 ld r0,16(r1) 98: a6 03 08 7c mtlr r0 9c: 20 00 80 4e blr Please, note that are used either 3 or 4 instructions before the mcount location depending on the compiler version. Best Regards, Petr