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Date: Mon, 26 Oct 2015 15:18:39 +0800
From: "Wangnan (F)" <wangnan0@huawei.com>
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To: Arnaldo Carvalho de Melo <acme@kernel.org>
CC: <ast@plumgrid.com>, <brendan.d.gregg@gmail.com>, <a.p.zijlstra@chello.nl>,
        <daniel@iogearbox.net>, <dsahern@gmail.com>, <hekuang@huawei.com>,
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        <masami.hiramatsu.pt@hitachi.com>, <namhyung@kernel.org>,
        <paulus@samba.org>, <linux-kernel@vger.kernel.org>, <pi3orama@163.com>,
        <xiakaixu@huawei.com>
Subject: Re: [PATCH 05/31] perf record: Load eBPF object into kernel
References: <1444826502-49291-1-git-send-email-wangnan0@huawei.com> <1444826502-49291-6-git-send-email-wangnan0@huawei.com> <20151023165840.GI27006@kernel.org> <20151024002708.GJ27006@kernel.org>
In-Reply-To: <20151024002708.GJ27006@kernel.org>
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Hi Arnaldo,

On 2015/10/24 8:27, Arnaldo Carvalho de Melo wrote:
> libbpf: load bpf program failed: Invalid argument
> libbpf: -- BEGIN DUMP LOG ---
> libbpf:
>
> libbpf: -- END LOG --
> libbpf: failed to load program 'fork=_do_fork'
> libbpf: failed to load object '/tmp/foo.o'
> bpf: load objects failed
> event syntax error: '/tmp/foo.o'
>                       \___ Invalid argument: Are you root and runing a CONFIG_BPF_SYSCALL kernel?
>
> (add -v to see detail)
> Run 'perf list' for a list of valid events
>
>   Usage: perf record [<options>] [<command>]
>      or: perf record [<options>] -- <command> [<options>]
>
>      -e, --event <event>   event selector. use 'perf list' to list available events
> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> Opening /sys/kernel/debug/tracing//uprobe_events write=1
> Parsing probe_events: p:perf_bpf_probe/fork _text+638512
> Group:perf_bpf_probe Event:fork probe:p
> Writing event: -:perf_bpf_probe/fork
> [acme@felicio linux]$ uname -a
> Linux felicio.ghostprotocols.net 4.3.0-rc6+ #1 SMP Fri Oct 23 16:40:25 BRT 2015 x86_64 x86_64 x86_64 GNU/Linux
> [acme@felicio linux]$
>
Please have a look at patch [1]. With that patch kernel will dump 
something into
log buffer. In your case, you will see:

root@sandybridge:~# /tmp/perf record -e /tmp/test_config_base.o ls
libbpf: load bpf program failed: Invalid argument
libbpf: -- BEGIN DUMP LOG ---
libbpf:
Kernel version mismatch: 0x40400 != 0x40300

libbpf: -- END LOG --
libbpf: failed to load program 'func_write=sys_write'
libbpf: failed to load object '/tmp/test_config_base.o'
event syntax error: '/tmp/test_config_base.o'
                      \___ Invalid argument: Are you root and runing a 
CONFIG_BPF_SYSCALL kernel?

(add -v to see detail)
Run 'perf list' for a list of valid events
...

And I'd like to improve the error message output by perf.

Do you want me to send a patch for fixing this problem or modifying 
existing patches
in my git tree?

Thank you.

[1] 
http://lkml.kernel.org/r/1445843588-143137-1-git-send-email-wangnan0@huawei.com