From: Torsten Duwe <duwe@lst.de>
To: Petr Mladek <pmladek@suse.com>
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 16:45:23 +0100 [thread overview]
Message-ID: <20160202154523.GF32095@lst.de> (raw)
In-Reply-To: <20160202121224.GS3305@pathway.suse.cz>
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.
> For example, the code generated for int_to_scsilun() looks like:
>
>
> 00000000000002d0 <int_to_scsilun>:
> 2d0: a6 02 08 7c mflr r0
> 2d4: 10 00 01 f8 std r0,16(r1)
> 2d8: 01 00 00 48 bl 2d8 <int_to_scsilun+0x8>
> 2d8: R_PPC64_REL24 _mcount
[...]
> The above code is generated from kernel-4.5-rc1 sources using
>
> $> gcc --version
> gcc (SUSE Linux) 4.8.5
>
> But I get similar code also with
>
> $> gcc-6 --version
> gcc-6 (SUSE Linux) 6.0.0 20160121 (experimental) [trunk revision 232670]
>
>
> 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.
> 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?
Torsten
next prev parent reply other threads:[~2016-02-02 15:45 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
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 [this message]
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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