From: Balbir Singh <bsingharora@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Torsten Duwe <duwe@lst.de>, Michael Ellerman <mpe@ellerman.id.au>,
Jiri Kosina <jkosina@suse.cz>, Miroslav Benes <mbenes@suse.cz>,
Jessica Yu <jeyu@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
live-patching@vger.kernel.org
Subject: Re: [PATCH v8 8/8] livepatch: Detect offset for the ftrace location during build
Date: Sat, 13 Feb 2016 12:33:00 +1100 [thread overview]
Message-ID: <1455327180.16012.14.camel@gmail.com> (raw)
In-Reply-To: <20160212164517.GO12548@pathway.suse.cz>
On Fri, 2016-02-12 at 17:45 +0100, Petr Mladek wrote:
> On Sat 2016-02-13 03:13:29, Balbir Singh wrote:
> > On Thu, 2016-01-28 at 16:32 +0100, Torsten Duwe wrote:
> > > From: Petr Mladek <pmladek@suse.com>
> > >
> > > Livepatch works on x86_64 and s390 only when the ftrace call
> > > is at the very beginning of the function. But PPC is different.
> > > We need to handle TOC and save LR there before calling the
> > > global ftrace handler.
> > >
> > > Now, the problem is that the extra operations have different
> > > length on PPC depending on the used gcc version. It is
> > > 4 instructions (16 bytes) before gcc-6 and only 3 instructions
> > > (12 bytes) with gcc-6.
> > >
> > > This patch tries to detect the offset a generic way during
> > > build. It assumes that the offset of the ftrace location
> > > is the same for all functions. It modifies the existing
> > > recordmcount tool that is able to find read mcount locations
> > > directly from the object files. It adds an option -p
> > > to print the first found offset.
> > >
> > > The recordmcount tool is then used in the kernel/livepatch
> > > subdirectory to generate a header file. It defines
> > > a constant that is used to compute the ftrace location
> > > from the function address.
> > >
> > > Finally, we have to enable the C implementation of the
> > > recordmcount tool to be used on PPC and S390. It seems
> > > to work fine there. It should be more reliable because
> > > it reads the standardized elf structures. The old perl
> > > implementation uses rather complex regular expressions
> > > to parse objdump output and is therefore much more tricky.
> >
> > I'm still missing something, I'm getting offset as 8
> >
> > When I run, I get
> >
> > scripts/recordmcount -p kernel/livepatch/core.o
> > #define KLP_FTRACE_LOCATION 8
> >
> > scripts/recordmcount -p kernel/livepatch/ftrace-test.o
> > #define KLP_FTRACE_LOCATION 8
> >
> > My sample fails as well, since the expected offset is 16.
> > I guess the script is being run against a not so good
> > test.
>
> I guess that you used a broken gcc and cheated the check
> to pass the compilation. Did you, please?
>
> The test used to detect the offset is using a minimalistic
> function is is afftected by the gcc bug.
>
> The patch below might be used to cheat the offset check as well.
>
> Torsten, please mention this somewhere if you, just by chance,
> send a new version of the patchset.
>
> From f6a438a3f2f60cc1acc859b41d0cc9259c9a331e Mon Sep 17 00:00:00 2001
> From: root <root@c79.arch.suse.de>
> Date: Tue, 2 Feb 2016 15:35:06 +0100
> Subject: [PATCH 2/2] livepatch: Make sure the TOC is handled when detecting
> ftrace location
>
> There seems to be a bug in gcc on PPC. It does not handle TOC
> if the function does not access global variables or functions
> by default. But it should when profiling is enabled.
>
Yep.. Please see see http://marc.info/?l=linux-kernel&m=145518015816435&w=2
and my question at http://marc.info/?l=linuxppc-embedded&m=145518330317496&w=2
> This patch works around this problem by adding a call
> to a global function.
>
> This patch is for testing only!
> ---
> kernel/livepatch/ftrace-test.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/kernel/livepatch/ftrace-test.c b/kernel/livepatch/ftrace-test.c
> index 22f0c54bf7b3..a3b7aabb67e5 100644
> --- a/kernel/livepatch/ftrace-test.c
> +++ b/kernel/livepatch/ftrace-test.c
> @@ -1,6 +1,9 @@
> /* Sample code to figure out mcount location offset */
> +#include
> +
>
> int test(int a)
> {
> + printk("%d\n", a);
> return ++a;
> }
This is much better, I see the offset of 16.
Balbir Singh
next prev parent reply other threads:[~2016-02-13 1:33 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-10 17:29 [PATCH v8 0/8] ftrace with regs + live patching for ppc64 LE (ABI v2) Torsten Duwe
2016-01-28 15:32 ` [PATCH v8 8/8] livepatch: Detect offset for the ftrace location during build Torsten Duwe
2016-02-12 16:13 ` Balbir Singh
2016-02-12 16:45 ` Petr Mladek
2016-02-13 1:33 ` Balbir Singh [this message]
2016-02-16 5:47 ` Kamalesh Babulal
2016-02-16 8:23 ` Torsten Duwe
2016-02-16 10:30 ` Kamalesh Babulal
2016-02-16 10:39 ` Torsten Duwe
2016-02-16 13:57 ` Petr Mladek
2016-02-17 3:08 ` Michael Ellerman
2016-02-23 17:00 ` Torsten Duwe
2016-02-24 6:37 ` Balbir Singh
2016-02-24 6:55 ` Balbir Singh
2016-02-24 9:23 ` Torsten Duwe
2016-02-24 11:22 ` Balbir Singh
2016-02-24 7:51 ` Kamalesh Babulal
2016-02-10 16:21 ` [PATCH v8 1/8] ppc64 (le): prepare for -mprofile-kernel Torsten Duwe
2016-02-17 10:55 ` Michael Ellerman
2016-02-17 11:30 ` Torsten Duwe
2016-02-17 11:39 ` Michael Ellerman
2016-02-10 16:22 ` [PATCH v8 2/8] ppc64le FTRACE_WITH_REGS implementation Torsten Duwe
2016-02-10 16:22 ` [PATCH v8 3/8] ppc use ftrace_modify_all_code default Torsten Duwe
2016-02-10 16:25 ` [PATCH v8 4/8] ppc64 ftrace_with_regs configuration variables Torsten Duwe
2016-02-11 7:48 ` Balbir Singh
2016-02-11 8:39 ` Kamalesh Babulal
2016-02-11 9:35 ` Balbir Singh
2016-02-11 13:00 ` Murali Sampath
2016-02-11 13:00 ` Murali Sampath
2016-02-11 8:42 ` Torsten Duwe
2016-02-11 9:34 ` Balbir Singh
2016-02-15 10:27 ` Michael Ellerman
2016-02-15 12:56 ` Jiri Kosina
2016-02-15 14:04 ` Torsten Duwe
2016-02-15 22:21 ` Torsten Duwe
2016-02-16 4:53 ` Balbir Singh
2016-02-16 10:09 ` Michael Ellerman
2016-02-16 10:35 ` Torsten Duwe
2016-02-10 16:27 ` [PATCH v8 5/8] ppc64 ftrace_with_regs: disable profiling for some files Torsten Duwe
2016-02-10 16:34 ` [PATCH v8 6/8] Implement kernel live patching for ppc64le (ABIv2) Torsten Duwe
2016-02-11 9:01 ` Miroslav Benes
2016-02-10 16:36 ` [PATCH v8 7/8] Enable LIVEPATCH to be configured on ppc64le and add livepatch.o if it is selected Torsten Duwe
2016-02-11 6:18 ` [PATCH v8 0/8] ftrace with regs + live patching for ppc64 LE (ABI v2) Balbir Singh
2016-02-11 8:38 ` Torsten Duwe
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