From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Wang Nan <wangnan0@huawei.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
brendan.d.gregg@gmail.com, bblanco@plumgrid.com
Subject: Re: perf test BPF failing on f24: fix
Date: Tue, 2 Aug 2016 23:15:34 -0300 [thread overview]
Message-ID: <20160803021534.GE14639@kernel.org> (raw)
In-Reply-To: <20160802210331.GA20688@ast-mbp.thefacebook.com>
Em Tue, Aug 02, 2016 at 02:03:33PM -0700, Alexei Starovoitov escreveu:
> On Tue, Aug 02, 2016 at 04:51:02PM -0300, Arnaldo Carvalho de Melo wrote:
> > Hi Wang,
> >
> > Something changed and a function used in a perf test for BPF is
> > not anymore appearing on vmlinux, albeit still available on
> > /proc/kallsyms:
> >
> > # readelf -wi /lib/modules/4.7.0+/build/vmlinux | grep -w sys_epoll_wait
> > #
> >
> > But:
> >
> > [root@jouet ~]# grep -i sys_epoll_wait /proc/kallsyms
> > ffffffffbd295b50 T SyS_epoll_wait
> > ffffffffbd295b50 T sys_epoll_wait
> > [root@jouet ~]#
> >
> > I noticed that it is some sort of aliasing so I checked the other
> > variant:
> >
> > [root@jouet ~]# readelf -wi /lib/modules/4.7.0+/build/vmlinux | grep -w SyS_epoll_wait
> > <2bc9b85> DW_AT_name : (indirect string, offset: 0xe7524): SyS_epoll_wait
> > [root@jouet ~]#
> >
> > Trying to use perf probe also produces the same resuls I notice when
> > running the perf test that is failing:
> >
> > [root@jouet ~]# perf probe sys_epoll_wait
> > Failed to find debug information for address ffffffffbd295b50
> > Probe point 'sys_epoll_wait' not found.
> > Error: Failed to add events.
> > [root@jouet ~]# perf probe SyS_epoll_wait
> > Added new events:
> > probe:SyS_epoll_wait (on SyS_epoll_wait)
> > probe:SyS_epoll_wait_1 (on SyS_epoll_wait)
> > probe:SyS_epoll_wait_2 (on SyS_epoll_wait)
>
> that change will break all sorts of scripts that relying on syscalls to start
> with sys_
Is there a promise that internal kernel functions will not change names?
> I guess we can workaround in user space, but what was the motivation to
> disable kprobe attach on sys_* while it's still in kallsyms?
Was it disabled? What I noticed whas that the sys_epoll_wait wasn't
present in the DWARF info present in the vmlinux file, which would be
good for others to confirm, which I'll check on other machines here at
home, tomorrow.
- Arnaldo
> >
> > You can now use it in all perf tools, such as:
> >
> > perf record -e probe:SyS_epoll_wait_2 -aR sleep 1
> >
> > [root@jouet ~]#
> >
> > So I am changing the BPF perf test to use the CamelCase notation alias:
> >
> > Failing (with sys_epoll_wait):
> >
> > [root@jouet ~]# perf test BPF
> > 37: Test BPF filter :
> > 37.1: Test basic BPF filtering : FAILED!
> > 37.2: Test BPF prologue generation : Skip
> > 37.3: Test BPF relocation checker : Skip
> > [root@jouet ~]#
> >
> > Changing to (SyS_epoll_wait):
> >
> > [root@jouet ~]# perf test BPF
> > 37: Test BPF filter :
> > 37.1: Test basic BPF filtering : Ok
> > 37.2: Test BPF prologue generation : Ok
> > 37.3: Test BPF relocation checker : Ok
> > [root@jouet ~]#
> >
> > I'm adding a fix that just makes it use SyS_epoll_wait.
> >
> > - Arnaldo
next prev parent reply other threads:[~2016-08-03 2:16 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-02 19:51 perf test BPF failing on f24: fix Arnaldo Carvalho de Melo
2016-08-02 21:03 ` Alexei Starovoitov
2016-08-03 2:15 ` Arnaldo Carvalho de Melo [this message]
2016-08-03 2:57 ` Alexei Starovoitov
2016-08-03 2:41 ` Wangnan (F)
2016-08-03 3:41 ` Wangnan (F)
2016-08-03 8:19 ` Wangnan (F)
2016-08-03 14:45 ` Masami Hiramatsu
2016-08-03 20:04 ` Arnaldo Carvalho de Melo
2016-08-04 6:32 ` Masami Hiramatsu
2016-08-04 12:48 ` Arnaldo Carvalho de Melo
2016-08-04 19:36 ` Arnaldo Carvalho de Melo
2016-08-04 21:47 ` Arnaldo Carvalho de Melo
2016-08-05 9:45 ` Masami Hiramatsu
2016-08-05 14:35 ` Arnaldo Carvalho de Melo
2016-08-05 15:55 ` Arnaldo Carvalho de Melo
2016-08-06 10:29 ` Masami Hiramatsu
2016-08-08 19:33 ` Arnaldo Carvalho de Melo
2016-08-09 19:17 ` [tip:perf/urgent] perf probe: Adjust map->reloc offset when finding kernel symbol from map tip-bot for Masami Hiramatsu
2016-08-03 23:08 ` perf test BPF failing on f24: fix Masami Hiramatsu
2016-08-04 1:50 ` Wangnan (F)
2016-08-04 8:47 ` Masami Hiramatsu
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