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[PATCH 11/11] perf report: Ensure the perf DSO mapping matches what libdw sees

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From: Milian Wolff <milian.wolff@kdab.com>

In some situations the libdw unwinder stopped working properly.  I.e.
with libunwind we see:

~~~~~
heaptrack_gui  2228 135073.400112:     641314 cycles:
	            e8ed _dl_fixup (/usr/lib/ld-2.25.so)
	           15f06 _dl_runtime_resolve_sse_vex (/usr/lib/ld-2.25.so)
	           ed94c KDynamicJobTracker::KDynamicJobTracker (/home/milian/projects/compiled/kf5/lib64/libKF5KIOWidgets.so.5.35.0)
	           608f3 _GLOBAL__sub_I_kdynamicjobtracker.cpp (/home/milian/projects/compiled/kf5/lib64/libKF5KIOWidgets.so.5.35.0)
	            f199 call_init.part.0 (/usr/lib/ld-2.25.so)
	            f2a5 _dl_init (/usr/lib/ld-2.25.so)
	             db9 _dl_start_user (/usr/lib/ld-2.25.so)
~~~~~

But with libdw and without this patch this sample is not properly
unwound:

~~~~~
heaptrack_gui  2228 135073.400112:     641314 cycles:
	            e8ed _dl_fixup (/usr/lib/ld-2.25.so)
	           15f06 _dl_runtime_resolve_sse_vex (/usr/lib/ld-2.25.so)
	           ed94c KDynamicJobTracker::KDynamicJobTracker (/home/milian/projects/compiled/kf5/lib64/libKF5KIOWidgets.so.5.35.0)
~~~~~

Debug output showed me that libdw found a module for the last frame
address, but it thinks it belongs to /usr/lib/ld-2.25.so. This patch
double-checks what libdw sees and what perf knows. If the mappings
mismatch, we now report the elf known to perf. This fixes the situation
above, and the libdw unwinder produces the same stack as libunwind.

Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20170602143753.16907-1-milian.wolff@kdab.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/unwind-libdw.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index b4c20124d2ee..da45c4be5fb3 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -39,6 +39,14 @@ static int __report_module(struct addr_location *al, u64 ip,
 		return 0;
 
 	mod = dwfl_addrmodule(ui->dwfl, ip);
+	if (mod) {
+		Dwarf_Addr s;
+
+		dwfl_module_info(mod, NULL, &s, NULL, NULL, NULL, NULL, NULL);
+		if (s != al->map->start)
+			mod = 0;
+	}
+
 	if (!mod)
 		mod = dwfl_report_elf(ui->dwfl, dso->short_name,
 				      dso->long_name, -1, al->map->start,
-- 
2.9.4

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[GIT PULL 00/11] perf/urgent fixes Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-06-06 21:30 +0200
  [PATCH 11/11] perf report: Ensure the perf DSO mapping matches what libdw sees Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-06-06 21:30 +0200
  [PATCH 01/11] perf annotate: Fix failure when filename has special chars Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-06-06 21:30 +0200
  [PATCH 05/11] perf header: Set proper module name when build-id event found Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-06-06 21:30 +0200
  [PATCH 06/11] perf symbols: Set module info when build-id event found Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-06-06 21:30 +0200
  [PATCH 08/11] perf test: Disable breakpoint signal tests for powerpc Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-06-06 21:30 +0200
  Re: [GIT PULL 00/11] perf/urgent fixes Ingo Molnar <mingo@kernel.org> - 2017-06-07 18:00 +0200

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