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From: Petr Mladek <pmladek@suse.com>
To: Torsten Duwe <duwe@lst.de>
Cc: Miroslav Benes <mbenes@suse.cz>,
	Steven Rostedt <rostedt@goodmis.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	anton@samba.org, Jiri Kosina <jkosina@suse.cz>,
	linuxppc-dev@lists.ozlabs.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	live-patching@vger.kernel.org
Subject: Re: [PATCH v6 8/9] Implement kernel live patching for ppc64le (ABIv2)
Date: Tue, 2 Feb 2016 17:47:14 +0100	[thread overview]
Message-ID: <20160202164714.GU3305@pathway.suse.cz> (raw)
In-Reply-To: <20160202154523.GF32095@lst.de>

On Tue 2016-02-02 16:45:23, Torsten Duwe wrote:
> On Tue, Feb 02, 2016 at 01:12:24PM +0100, Petr Mladek wrote:
> > 
> > Hmm, the size of the offset is not a constant. In particular, leaf
> > functions do not set TOC before the mcount location.
> 
> To be slightly more precise, a leaf function that additionally uses
> no global data. No global function calls, no global data access =>
> no need to load the TOC.

Thanks for explanation.
 
> > The result is that kernel crashes when trying to trace leaf function
> 
> The trampoline *requires* a proper TOC pointer to find the remote function
> entry point. If you jump onto the trampoline with the TOC from the caller's
> caller you'll grab some address from somewhere and jump into nirvana.

The dmesg messages suggested someting like this.


> > By other words, it seems that the code generated with -mprofile-kernel
> > option has been buggy in all gcc versions.
> 
> Either that or we need bigger trampolines for everybody.
> 
> Michael, should we grow every module trampoline to always load R2,
> or fix GCC to recognise the generated bl _mcount as a global function call?
> Anton, what do you think?

BTW: Is the trampoline used also for classic probes? If not, we might need
a trampoline for them as well.

Note that TOC is not set only when the problematic functions are
compiled with --mprofile-kernel. I still see the TOC stuff when
compiling only with -pg.


Best Regards,
Petr

  reply	other threads:[~2016-02-02 16:47 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
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 [this message]
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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