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Message-ID: <CAKTCnznB8WQGbuJkek7nhnXW6FSBR+Mk__jeNfpgfpTf8G9MMA@mail.gmail.com> Date: Fri, 5 Feb 2016 15:40:27 +1100 From: Balbir Singh <bsingharora@...il.com> To: Petr Mladek <pmladek@...e.com> Cc: AKASHI Takahiro <takahiro.akashi@...aro.org>, Jiri Kosina <jikos@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Steven Rostedt <rostedt@...dmis.org>, Torsten Duwe <duwe@....de>, live-patching@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org Subject: Re: [PATCH v6 1/9] ppc64 (le): prepare for -mprofile-kernel On Thu, Feb 4, 2016 at 10:02 PM, Petr Mladek <pmladek@...e.com> wrote: > 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 >> <prologue> >> ... >> <body> >> ... > > 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 <cmdline_proc_show>: > 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 <cmdline_proc_show+0xc> > 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 <cmdline_proc_show+0x30> > 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 <cmdline_proc_show>: > 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 <cmdline_proc_show+0x10> > 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 <cmdline_proc_show+0x34> > 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. Thanks Petr For big endian builds I saw Dump of assembler code for function alloc_pages_current: 0xc000000000256f00 <+0>: mflr r0 0xc000000000256f04 <+4>: std r0,16(r1) 0xc000000000256f08 <+8>: bl 0xc000000000009e5c <.mcount> 0xc000000000256f0c <+12>: mflr r0 The offset is 8 bytes. Your earlier patch handled this by adding 16, I suspect it needs revisiting Balbir
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