linux-kernel - Re: [PATCH v2] perf tools: fix off-by-one error in maps

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Message-ID: <CABPqkBSMapWzo5k7WXpt8Ejtdvk_znX1P6xV0eYRpK7rcTjjZw@mail.gmail.com>
Date:	Tue, 7 Oct 2014 16:17:41 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH v2] perf tools: fix off-by-one error in maps

On Tue, Oct 7, 2014 at 4:00 PM, Arnaldo Carvalho de Melo
<acme@...hat.com> wrote:
> Em Tue, Oct 07, 2014 at 02:47:19PM +0900, Namhyung Kim escreveu:
>> On Mon, 6 Oct 2014 10:35:32 +0200, Stephane Eranian wrote:
>> > This patch fixes off-by-one errors in the management of maps.
>> > A map is defined by start address and length as implemented by map__new():
>
>> > map__init(map, type, start, start + len, pgoff, dso);
>
>> > map->start = addr;
>> > map->end = end;
>
>> > Consequently, the actual address range is ]start; end[
>> > map->end is the first byte outside the range. This patch
>> > fixes two bugs where upper bound checking was off-by-one.
>
>> > In V2, we fix map_groups__fixup_overlappings() some more
>> > where map->start was off-by-one as reported by Jiri.
>
>> It seems we also need to fix maps__find():
>
>> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
>> index b7090596ac50..107a8c90785b 100644
>> --- a/tools/perf/util/map.c
>> +++ b/tools/perf/util/map.c
>> @@ -752,7 +752,7 @@ struct map *maps__find(struct rb_root *maps, u64 ip)
>>                 m = rb_entry(parent, struct map, rb_node);
>>                 if (ip < m->start)
>>                         p = &(*p)->rb_left;
>> -               else if (ip > m->end)
>> +               else if (ip >= m->end)
>>                         p = &(*p)->rb_right;
>>                 else
>>                         return m;
>
> I keep thinking that this change is making things unclear.
>
> I.e. the _start_ of a map (map->start) is _in_ the map, and the _end_
> of a map (map->end) is _in_ the map as well.
>
>         if (addr > m->end)
>
> is shorter than:
>
>         if (addr >= m->end)
>
> "start" and "end" should have the same rule applied, i.e. if one is in,
> the other is in as well.
>
It is okay but then we need to be consistent all across. This is not
the case today.
I mentioned the cases I ran into.

> Etc.
>
> - Arnaldo
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