From: AKASHI Takahiro <takahiro.akashi@linaro.org>
To: Torsten Duwe <duwe@lst.de>, Jiri Kosina <jikos@kernel.org>
Cc: 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: Thu, 4 Feb 2016 18:31:40 +0900 [thread overview]
Message-ID: <56B31A7C.2050803@linaro.org> (raw)
In-Reply-To: <20160203112449.GA27247@lst.de>
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>
...
>> 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.
I don't want to bother you, but for my better understandings, could you show me
an example of asm instructions for a function prologue under -mprofile-kernel, please?
-Takahiro AKASHI
> This proposal, if implemented in a too naive fashion, will worsen the problem
> we currently discuss: a few NOPs _never_ cause any global reference. GCC might
> be even more inclined to not load a new TOC value. That change would need to be
> fairly smart on ppc64le.
>
> Torsten
>
next prev parent reply other threads:[~2016-02-04 9:31 UTC|newest]
Thread overview: 42+ 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 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
2016-02-03 7:23 ` AKASHI Takahiro
2016-02-03 8:55 ` Jiri Kosina
2016-02-03 11:24 ` Torsten Duwe
2016-02-04 9:31 ` AKASHI Takahiro [this message]
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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