linux-kernel - Re: [PATCH] perf: fix a segfault problem.

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Message-ID: <20150313112046.GA28773@danjae.skbroadband>
Date:	Fri, 13 Mar 2015 20:20:46 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	acme@...nel.org, jolsa@...nel.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, lizefan@...wei.com, pi3orama@....com
Subject: Re: [PATCH] perf: fix a segfault problem.

On Fri, Mar 13, 2015 at 06:07:34PM +0800, Wang Nan wrote:
> On 2015/3/13 17:46, Namhyung Kim wrote:
> > On Fri, Mar 13, 2015 at 08:41:32AM +0000, Wang Nan wrote:
> >> Without this patch, perf report cause segfault if pass "" as '-t':
> >>
> >>   $ perf report -t ""
> >>
> >>     # To display the perf.data header info, please use --header/--header-only options.
> >>     #
> >>     # Samples: 37  of event 'syscalls:sys_enter_write'
> >>     # Event count (approx.): 37
> >>     #
> >>     # Children    SelfCommand   Shared Object         Symbol
> >>     Segmentation fault
> >>
> >> This patch avoid the segfault by checking empty string for
> >> 'symbol_conf.field_sep'.
> > 
> > What about resetting it to NULL if empty string was given?
> > 
> 
> In fact I'm not very clear why we need such 'symbol_conf.field_sep', so I'm
> not sure whether '-t ""' is totally meanless or not.
> 
> -t option replaces a group of character with '.' and appends them after a field.
> With -t 'abc' I get something like:
> 
>  #
>  # OverheadabcCommand   abcShared Object    abcSymbol
>   100.00%abcb.beltr.ceabc[kernel.k.llsyms]abc[k] 0xffffffff810118f0
>   ...
> 
> Hard to read...
> 
> I read docs and your commit messages, but still not understand the option. Could you
> please explain the goal and usage of that option again?

Well, I'm not the person who wrote the doc and introduced this
option. ;-)

Anyway AFAIK it's to generate a CSV file so usual value would be ','.
To reduce possible confusion due to the separation character in the
original output, it replaces the character during the generation.

Thanks,
Namhyung
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