linux-kernel - Re: [PATCH -tip perf/probes 00/10] x86 insn decoder bugfixes

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Message-ID: <4AE9FA43.1040803@redhat.com>
Date:	Thu, 29 Oct 2009 13:25:39 -0700
From:	Josh Stone <jistone@...hat.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jim Keniston <jkenisto@...ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jason Baron <jbaron@...hat.com>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip perf/probes 00/10] x86 insn decoder bugfixes

On 10/29/2009 01:10 PM, Masami Hiramatsu wrote:
> Masami Hiramatsu wrote:
>> Ingo Molnar wrote:
>>> Another problem i noticed is that a vmlinux without DEBUG_INFO will fail
>>> in this way:
>>>
>>>    aldebaran:~/linux/linux>   perf probe schedule
>>>      Fatal: Failed to call dwarf_init(). Maybe, not a dwarf file.
>>
>> Ah, really? I think I broke need_dwarf logic somehow...
> 
> Hmm, I've found that is for searching (implicitly) inlined symbols,
> this means "the behavior is by (bad) design" :-(
> 
> I think it should be search the symbol in Elf (or kallsyms) first,
> and only if it fails, use Dwarf for searching the symbol again.
> 
> Or, it may be enough that just trying to setup probe and if it fails
> use Dwarf. This way doesn't require any vmlinux access.

Just beware that functions can exist in the symbol table and as inlines
at the same time.  For example, we've seen compat_sys_recvmsg get
inlined into compat_sys_socketcall, while it's still compiled as a
standalone function too.  So if you have the dwarf, you should still try
to see if inlined versions exist.

Josh
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