linux-kernel - Re: [PATCH 1/3] perf probe: Set retprobe flag when probe in address-based alternative mode

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Date:	Mon, 13 Apr 2015 11:42:41 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	He Kuang <hekuang@...wei.com>
Cc:	masami.hiramatsu.pt@...achi.com, a.p.zijlstra@...llo.nl,
	mingo@...hat.com, namhyung@...nel.org, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] perf probe: Set retprobe flag when probe in
 address-based alternative mode

Em Mon, Apr 13, 2015 at 11:39:03AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Apr 13, 2015 at 07:41:28PM +0800, He Kuang escreveu:
> > Perf probe misses to set retprobe flag back when falling back to
> > address-based alternative mode.
 
> Humm, noticed one other problem, but not with your patch, about this message:
 
> "Could not open debuginfo. Try to use symbols."
 
> That is really not clear, specially that "try to use symbols" :-)
 
> [root@...andy ~]# ls -la /root/.debug/.build-id/dd/32e51921ede0fd46f034091b7f6a0f2e01ebda
> lrwxrwxrwx. 1 root root 86 Apr 10 18:02 /root/.debug/.build-id/dd/32e51921ede0fd46f034091b7f6a0f2e01ebda -> ../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda
> [root@...andy ~]# ls -la /root/.debug/.build-id/dd/../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda 
> -rwxr-xr-x. 1 root root 22698661 Apr 10 18:02 /root/.debug/.build-id/dd/../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda
> [root@...andy ~]# ls -la /root/.debug/.build-id/dd/../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda
 
> I.e. it managed to read the debuginfo, its just that it has no symbols in it :-)
 
> Anyway, digression ended.

Interesting is that when testing your next patch I see:

  [root@...andy linux]#  perf probe -s ./kernel_src/ --add='fs/super.c;s->s_count=1;'
  The /root/.debug/.build-id/dd/32e51921ede0fd46f034091b7f6a0f2e01ebda file has no debug information.
  Rebuild with CONFIG_DEBUG_INFO=y, or install an appropriate debuginfo package.
    Error: Failed to add events.
  [root@...andy linux]# 

Much, much clear message about that debuginfo file :-)

But then, to test your [2/3] patch I'll have to figure out how to setup the
environment so that I can match your results, shouldn't be hard, but would
save reviewing time if you stated it in the commit log message.

- Arnaldo
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