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From: Jiri Kosina <jikos@kernel.org>
To: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Torsten Duwe <duwe@lst.de>, Steven Rostedt <rostedt@goodmis.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	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
Date: Wed, 3 Feb 2016 09:55:11 +0100 (CET)	[thread overview]
Message-ID: <alpine.LNX.2.00.1602030952220.22727@cbobk.fhfr.pm> (raw)
In-Reply-To: <56B1AAE5.10500@linaro.org>

On Wed, 3 Feb 2016, AKASHI Takahiro wrote:

> > The gcc switch -mprofile-kernel, available for ppc64 on gcc > 4.8.5,
> > allows to call _mcount very early in the function, which low-level
> > ASM code and code patching functions need to consider.
> > Especially the link register and the parameter registers are still
> > alive and not yet saved into a new stack frame.
> 
> I'm thinking of implementing live patch support *for arm64*, and as part of
> 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.
> So we have to initialize those codes at the boot time to later utilize
> them for FTRACE_WITH_REGS. Other than that, it will work similarly
> with -mfentry on x86 (and -mprofile-kernel?).
> 
> I'm totally unfamiliar with ppc architecture, but just wondering
> whether this option will also be useful for other architectures.

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 :) 
The part of the prologue where TOC pointer is saved needs to happen before 
the fentry/profiling call.

I don't think this will be an issue on ARM64, but it definitely is 
something that should be taken into account in case the gcc option is 
meant to be really generic.

Thanks,

-- 
Jiri Kosina
SUSE Labs

  reply	other threads:[~2016-02-03  8:55 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-25 15:38 [PATCH v6 0/9] ftrace with regs + live patching for ppc64 LE (ABI v2) Torsten Duwe
2016-01-25 15:26 ` [PATCH v6 1/9] ppc64 (le): prepare for -mprofile-kernel Torsten Duwe
2016-01-27 10:19   ` Michael Ellerman
2016-01-27 10:44     ` Torsten Duwe
2016-01-28  4:26       ` Michael Ellerman
2016-01-28  4:26         ` Michael Ellerman
2016-01-28 11:50         ` Torsten Duwe
2016-01-27 12:58     ` Alan Modra
2016-01-27 13:45       ` Torsten Duwe
2016-01-28  3:39       ` Michael Ellerman
2016-01-28  3:39         ` Michael Ellerman
2016-02-03  7:23   ` AKASHI Takahiro
2016-02-03  8:55     ` Jiri Kosina [this message]
2016-02-03 11:24       ` Torsten Duwe
2016-02-04  9:31         ` AKASHI Takahiro
2016-02-04 11:02           ` Petr Mladek
2016-02-05  4:40             ` Balbir Singh
2016-02-05 10:22               ` Petr Mladek
2016-02-04 21:47           ` Jiri Kosina
2016-01-25 15:27 ` [PATCH v6 2/9] ppc64le FTRACE_WITH_REGS implementation Torsten Duwe
2016-01-25 15:29 ` [PATCH v6 3/9] ppc use ftrace_modify_all_code default Torsten Duwe
2016-01-25 15:29 ` [PATCH v6 4/9] ppc64 ftrace_with_regs configuration variables Torsten Duwe
2016-01-25 15:30 ` [PATCH v6 5/9] ppc64 ftrace_with_regs: spare early boot and low level Torsten Duwe
2016-01-25 15:31 ` [PATCH v6 6/9] ppc64 ftrace: disable profiling for some functions Torsten Duwe
2016-01-25 15:31 ` [PATCH v6 7/9] ppc64 ftrace: disable profiling for some files Torsten Duwe
2016-01-25 15:33 ` [PATCH v6 8/9] Implement kernel live patching for ppc64le (ABIv2) Torsten Duwe
2016-01-26 10:50   ` Miroslav Benes
2016-01-26 12:48     ` Petr Mladek
2016-01-26 13:56       ` Torsten Duwe
2016-02-02 12:12       ` Petr Mladek
2016-02-02 15:45         ` Torsten Duwe
2016-02-02 16:47           ` Petr Mladek
2016-02-02 20:39             ` Jiri Kosina
2016-01-26 14:00     ` Torsten Duwe
2016-01-26 14:14       ` Miroslav Benes
2016-01-27  1:53         ` Jessica Yu
2016-02-02 13:46   ` [PATCH v6 8/9] " Denis Kirjanov
2016-02-10 18:03     ` Torsten Duwe
2016-01-25 15:33 ` [PATCH v6 9/9] Enable LIVEPATCH to be configured on ppc64le and add livepatch.o if it is selected Torsten Duwe
2016-01-27 10:51 ` [PATCH v6 0/9] ftrace with regs + live patching for ppc64 LE (ABI v2) Balbir Singh
2016-01-27 12:19   ` Torsten Duwe
2016-01-28  2:41     ` Balbir Singh
2016-01-28  3:31       ` Michael Ellerman
2016-01-28 11:19         ` Torsten Duwe

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