perf symbols: Take into account symfs setting when reading file build ID

After commit 5baecbcd9c9a ("perf symbols: we can now read separate
debug-info files based on a build ID") and when --symfs option is used
perf failed to pick up symbols for file with the same name between host
and sysroot specified by --symfs option.  One can see message like this:

  bin/bash with build id 26f0062cb6950d4d1ab0fd9c43eae8b10ca42062 not found, continuing without symbols

It happens because code added by 5baecbcd9c9a opens files directly by
dso->long_name without symbol_conf.symfs consideration, which as result
picks one from the host. It reads its build ID and later even code finds
another proper file in directory pointed by --symfs perf ignores it
because build id mismatches.

Fix is to use __symbol__join_symfs to adjust file name according to
--symfs setting. If no --symfs passed the operation would noop and picks
the same host file as before.

Also note in latter tree after 5baecbcd9c9a commit additional check for
'!dso->has_build_id' was added, so to observe error condition 'perf
record' should run with --no-buildid, so perf.data itself would not have
build id for target binary in buildid perf section and 'perf report'
will pass '!dso->has_build_id' condition. Or target binary should not
have build id, but the same binary on host has build id, again
'!dso->has_build_id' will pass in this case and incorrect build id could
be read if --symfs is used.

Signed-off-by: Victor Kamensky <kamensky@cisco.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Chris Phlipot <cphlipot0@gmail.com>
Cc: Dima Kogan <dima@secretsauce.net>
Cc: He Kuang <hekuang@huawei.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: xe-linux-external@cisco.com
Fixes: 5baecbcd9c9a ("perf symbols: we can now read separate debug-info files based on a build ID")
Link: http://lkml.kernel.org/r/1486424908-17094-1-git-send-email-kamensky@cisco.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.c

@@ -1460,9 +1460,11 @@ int dso__load(struct dso *dso, struct map *map)
 	 * DSO_BINARY_TYPE__BUILDID_DEBUGINFO to work
 	 */
 	if (!dso->has_build_id &&
-	    is_regular_file(dso->long_name) &&
-	    filename__read_build_id(dso->long_name, build_id, BUILD_ID_SIZE) > 0)
+	    is_regular_file(dso->long_name)) {
+	    __symbol__join_symfs(name, PATH_MAX, dso->long_name);
+	    if (filename__read_build_id(name, build_id, BUILD_ID_SIZE) > 0)
 		dso__set_build_id(dso, build_id);
+	}
 
 	/*
 	 * Iterate over candidate debug images.