From: Petr Mladek <pmladek@suse.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Torsten Duwe <duwe@lst.de>, Steven Rostedt <rostedt@goodmis.org>,
Michael Ellerman <mpe@ellerman.id.au>,
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 13:12:24 +0100 [thread overview]
Message-ID: <20160202121224.GS3305@pathway.suse.cz> (raw)
In-Reply-To: <20160126124853.GL3305@pathway.suse.cz>
On Tue 2016-01-26 13:48:53, Petr Mladek wrote:
> On Tue 2016-01-26 11:50:25, Miroslav Benes wrote:
> >
> > [ added Petr to CC list ]
> >
> > On Mon, 25 Jan 2016, Torsten Duwe wrote:
> >
> > > * create the appropriate files+functions
> > > arch/powerpc/include/asm/livepatch.h
> > > klp_check_compiler_support,
> > > klp_arch_set_pc
> > > arch/powerpc/kernel/livepatch.c with a stub for
> > > klp_write_module_reloc
> > > This is architecture-independent work in progress.
> > > * introduce a fixup in arch/powerpc/kernel/entry_64.S
> > > for local calls that are becoming global due to live patching.
> > > And of course do the main KLP thing: return to a maybe different
> > > address, possibly altered by the live patching ftrace op.
> > >
> > > Signed-off-by: Torsten Duwe <duwe@suse.de>
> >
> > Hi,
> >
> > I have a few questions...
> >
> > We still need Petr's patch from [1] to make livepatch work, right? Could
> > you, please, add it to this patch set to make it self-sufficient?
> >
> > Second, what is the situation with mcount prologue between gcc < 6 and
> > gcc-6? Are there only 12 bytes in gcc-6 prologue? If yes, we need to
> > change Petr's patch to make it more general and to be able to cope with
> > different prologues. This is unfortunate. Either way, please mention it
> > somewhere in a changelog.
>
> I am going to update the extra patch. There is an idea to detect the
> offset during build by scrips/recordmcount. This tool looks for the
> ftrace locations. The offset should always be a constant that depends
> on the used architecture, compiler, and compiler flags.
>
> The tool is called post build. We might need to pass the constant
> as a symbol added to the binary. The tool already adds some symbols.
Hmm, the size of the offset is not a constant. In particular, leaf
functions do not set TOC before the mcount location.
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
2dc: a6 02 08 7c mflr r0
2e0: 10 00 01 f8 std r0,16(r1)
2e4: e1 ff 21 f8 stdu r1,-32(r1)
2e8: 00 00 20 39 li r9,0
2ec: 00 00 24 f9 std r9,0(r4)
2f0: 04 00 20 39 li r9,4
2f4: a6 03 29 7d mtctr r9
2f8: 00 00 40 39 li r10,0
2fc: 02 c2 68 78 rldicl r8,r3,56,8
300: 78 23 89 7c mr r9,r4
304: ee 51 09 7d stbux r8,r9,r10
308: 02 00 4a 39 addi r10,r10,2
30c: 01 00 69 98 stb r3,1(r9)
310: 02 84 63 78 rldicl r3,r3,48,16
314: e8 ff 00 42 bdnz 2fc <int_to_scsilun+0x2c>
318: 20 00 21 38 addi r1,r1,32
31c: 10 00 01 e8 ld r0,16(r1)
320: a6 03 08 7c mtlr r0
324: 20 00 80 4e blr
328: 00 00 00 60 nop
32c: 00 00 42 60 ori r2,r2,0
Note that non-leaf functions starts with
0000000000000330 <scsi_set_sense_information>:
330: 00 00 4c 3c addis r2,r12,0
330: R_PPC64_REL16_HA .TOC.
334: 00 00 42 38 addi r2,r2,0
334: R_PPC64_REL16_LO .TOC.+0x4
338: a6 02 08 7c mflr r0
33c: 10 00 01 f8 std r0,16(r1)
340: 01 00 00 48 bl 340 <scsi_set_sense_information+0x10>
340: R_PPC64_REL24 _mcount
The above code is generated from kernel-4.5-rc1 sources 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.
But I get similar code also with
$> gcc-6 --version
gcc-6 (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.
The result is that kernel crashes when trying to trace leaf function
from modules. The mcount location is replaced with a call (branch)
that does not work without the TOC stuff.
By other words, it seems that the code generated with -mprofile-kernel
option has been buggy in all gcc versions.
I am curious that nobody found this earlier. Do I something wrong,
please?
Best Regards,
Petr
next prev parent reply other threads:[~2016-02-02 12:12 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 [this message]
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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