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[PATCH 07/15] perf symbols: Fix handling of zero-length symbols.

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From: Chris Phlipot <cphlipot0@gmail.com>

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.

1. addr_location is created for a sample, but symbol is unable to be
   resolved.

2. db export creates an "unknown" symbol of length zero at that address
   and inserts it into the dso.

3. A new sample comes in at the same address, but symbol__find is unable
   to find the zero length symbol, so it is still unresolved.

4. db export sees the symbol is unresolved, and allocated a duplicate
   symbol, even though it already did this in step 2.

This behavior continues every time an address without symbol information
is seen, which causes a very large number of these symbols to be
allocated.

The effect of this fix can be observed by looking at the contents of an
exported database before/after the fix (generated with
scripts/python/export-to-postgresql.py)

Ex.
BEFORE THE CHANGE:

  example_db=# select count(*) from symbols;
   count
  --------
   900213
  (1 row)

  example_db=# select count(*) from symbols where symbols.name='unknown';
   count
  --------
   897355
  (1 row)

  example_db=# select count(*) from symbols where symbols.name!='unknown';
   count
  -------
    2858
  (1 row)

AFTER THE CHANGE:

  example_db=# select count(*) from symbols;
   count
  -------
   25217
  (1 row)

  example_db=# select count(*) from symbols where name='unknown';
   count
  -------
   22359
  (1 row)

  example_db=# select count(*) from symbols where name!='unknown';
   count
  -------
    2858
  (1 row)

Signed-off-by: Chris Phlipot <cphlipot0@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1462612620-25008-1-git-send-email-cphlipot0@gmail.com
[ Moved the test to later in the rb_tree tests, as this not the likely case ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/symbol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 415c4f6d98fd..2946295ca502 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;
-- 
2.5.5

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[GIT PULL 00/15] perf/core improvements and fixes Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 09/15] perf probe: Check the return value of strbuf APIs Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 04/15] perf tools: Support reading from backward ring buffer Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 15/15] perf tools: Remove xrealloc and ALLOC_GROW Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 03/15] perf script: Fix incorrect python db-export error message Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 11/15] perf tools: Make alias handler to check return value of strbuf Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 14/15] perf help: Do not use ALLOC_GROW in add_cmd_list Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 07/15] perf symbols: Fix handling of zero-length symbols. Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 12/15] perf header: Make topology checkers to check return value of strbuf Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 05/15] perf tests: Add test to check backward ring buffer Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 01/15] perf callchain: Recording 'dwarf' callchains do not need DWARF unwinding support Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 06/15] perf evsel: Print state of perf_event_attr.write_backward Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 10/15] perf help: Make check_emacsclient_version to check strbuf APIs Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:20 +0200
  [PATCH 08/15] perf tools: Rewrite strbuf not to die() Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:30 +0200
  [PATCH 02/15] perf stat: Scale values by unit before metrics Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:30 +0200
  [PATCH 13/15] perf pmu: Make pmu_formats_string to check return value of strbuf Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-10 17:30 +0200
  Re: [GIT PULL 00/15] perf/core improvements and fixes Ingo Molnar <mingo@kernel.org> - 2016-05-10 22:30 +0200

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