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Date: Wed, 27 May 2015 09:50:21 -0300
From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Richard Weinberger <richard@nod.at>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Ahern <dsahern@gmail.com>, namhyung@kernel.org,
        Jiri Olsa <jolsa@redhat.com>, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH perf/core 1/2] [RESEND] perf probe: Show the error reason
 comes from invalid DSO
Message-ID: <20150527125021.GR17970@kernel.org>
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Em Wed, May 27, 2015 at 05:37:18PM +0900, Masami Hiramatsu escreveu:
> Show the reason of error when dso__load* failed. This shows
> when user gives wrong kernel image or wrong path.
 
> Without this, perf probe shows an obscure message.
>   ----
>   $ perf probe -k ~/kbin/linux-3.x86_64/vmlinux -L vfs_read
>   Failed to find path of kernel module.
>     Error: Failed to show lines.
>   ----
 
> With this, perf shows appropriate error message.
>   ----
>   $ perf probe -k ~/kbin/linux-3.x86_64/vmlinux -L vfs_read
>   Failed to find the path for kernel: Mismatching build id
>     Error: Failed to show lines.
>   ----
> And
>   ----
>   $ perf probe -k /non-exist/kernel/vmlinux -L vfs_read
>   Failed to find the path for kernel: No such file or directory
>     Error: Failed to show lines.
>   ----

Its better than before, and I am applying it.

But please consider to change the message further, because when one
specifies the vmlinux file to use with -k/--vmlinux, the tool is not
trying to "find the path for kernel", it is trying to use a specific
vmlinux file.

I.e. the messages above are good if we do:

  perf probe -L vfs_read

Here it _will_ try to find the path, as none was given.

So, when -k/--vmlinux is used, I suggest that the message be:

  $ perf probe -k ~/kbin/linux-3.x86_64/vmlinux -L vfs_read
  The kernel file "~/kbin/linux-3.x86_64/vmlinux" could not be used: Mismatching build id
    Error: Failed to show lines.

And:

  $ perf probe -k /non-exist/kernel/vmlinux -L vfs_read
  The kernel file "/non-exist/kernel/vmlinux" could not be used: No such file or directory
    Error: Failed to show lines.

Thanks!

- Arnaldo