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

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Message-ID: <20141007151035.GC2256@redhat.com>
Date:	Tue, 7 Oct 2014 12:10:35 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Stephane Eranian <eranian@...gle.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

Em Tue, Oct 07, 2014 at 04:17:41PM +0200, Stephane Eranian escreveu:
> 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.

Ok, and provided a patch doing the way I thought was confusing, now its
my turn to use that info and come up with a patch, ok, will do that.

- Arnaldo
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