linux-kernel - Re: [PATCH 1/2] perf tools: fix handling of zero-length symbols.

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Date:	Mon, 9 May 2016 10:51:24 -0700
From:	Chris Phlipot <cphlipot0@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	adrian.hunter@...el.com, peterz@...radead.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf tools: fix handling of zero-length symbols.


> On May 9, 2016, at 10:06 AM, Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> wrote:
> 
> Em Sat, May 07, 2016 at 02:16:59AM -0700, Chris Phlipot escreveu:
>> This change introduces a fix to symbols__find, so that it is able to find
>> symbols of length zero (where start==end)
>> 
>> The current code has the following problem:
>> -The current implementation of symbols__find is unable to find any symbols
>> of length zero.
>> -The db-export framework explicitly creates zero length symbols at
>> locations where no symbol currently exists.
>> 
>> The combination of the two above behaviors results in behavior similar to
>> the example below.
> 
> Ok, but you made the unlikely case be the first test, how about this one
> liner instead?
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 415c4f6d98fd..7a0917569fb3 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -301,7 +301,7 @@ static struct symbol *symbols__find(struct rb_root *symbols, u64 ip)
> 
>        if (ip < s->start)
>            n = n->rb_left;
> -        else if (ip >= s->end)
> +        else if (ip > s->end || (ip == s->end && ip != s->start)
>            n = n->rb_right;
>        else
>            return s;
> 
> 

I agree. This looks like a better fix.

>> +++ b/tools/perf/util/symbol.c
>> @@ -299,7 +299,9 @@ static struct symbol *symbols__find(struct rb_root *symbols, u64 ip)
>>    while (n) {
>>        struct symbol *s = rb_entry(n, struct symbol, rb_node);
>> 
>> -        if (ip < s->start)
>> +        if (ip == s->start && s->start == s->end)
>> +            return s;
>> +        else if (ip < s->start)
>>            n = n->rb_left;
>>        else if (ip >= s->end)
>>            n = n->rb_right;
>> -- 
>> 2.7.4