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

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Message-ID: <20141007140050.GB2256@redhat.com>
Date:	Tue, 7 Oct 2014 11:00:50 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, jolsa@...hat.com,
	peterz@...radead.org, mingo@...e.hu, dsahern@...il.com
Subject: Re: [PATCH v2] perf tools: fix off-by-one error in maps

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.

Etc.

- Arnaldo
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