perf test: Avoid an msan warning in a copied stack.

This fix is for a failure that occurred in the DWARF unwind perf test.

Stack unwinders may probe memory when looking for frames.

Memory sanitizer will poison and track uninitialized memory on the
stack, and on the heap if the value is copied to the heap.

This can lead to false memory sanitizer failures for the use of an
uninitialized value.

Avoid this problem by removing the poison on the copied stack.

The full msan failure with track origins looks like:

==2168==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x559ceb10755b in handle_cfi elfutils/libdwfl/frame_unwind.c:648:8
    #1 0x559ceb105448 in __libdwfl_frame_unwind elfutils/libdwfl/frame_unwind.c:741:4
    #2 0x559ceb0ece90 in dwfl_thread_getframes elfutils/libdwfl/dwfl_frame.c:435:7
    #3 0x559ceb0ec6b7 in get_one_thread_frames_cb elfutils/libdwfl/dwfl_frame.c:379:10
    #4 0x559ceb0ec6b7 in get_one_thread_cb elfutils/libdwfl/dwfl_frame.c:308:17
    #5 0x559ceb0ec6b7 in dwfl_getthreads elfutils/libdwfl/dwfl_frame.c:283:17
    #6 0x559ceb0ec6b7 in getthread elfutils/libdwfl/dwfl_frame.c:354:14
    linux-sunxi#7 0x559ceb0ec6b7 in dwfl_getthread_frames elfutils/libdwfl/dwfl_frame.c:388:10
    linux-sunxi#8 0x559ceaff6ae6 in unwind__get_entries tools/perf/util/unwind-libdw.c:236:8
    linux-sunxi#9 0x559ceabc9dbc in test_dwarf_unwind__thread tools/perf/tests/dwarf-unwind.c:111:8
    linux-sunxi#10 0x559ceabca5cf in test_dwarf_unwind__compare tools/perf/tests/dwarf-unwind.c:138:26
    linux-sunxi#11 0x7f812a6865b0 in bsearch (libc.so.6+0x4e5b0)
    linux-sunxi#12 0x559ceabca871 in test_dwarf_unwind__krava_3 tools/perf/tests/dwarf-unwind.c:162:2
    linux-sunxi#13 0x559ceabca926 in test_dwarf_unwind__krava_2 tools/perf/tests/dwarf-unwind.c:169:9
    linux-sunxi#14 0x559ceabca946 in test_dwarf_unwind__krava_1 tools/perf/tests/dwarf-unwind.c:174:9
    linux-sunxi#15 0x559ceabcae12 in test__dwarf_unwind tools/perf/tests/dwarf-unwind.c:211:8
    linux-sunxi#16 0x559ceabbc4ab in run_test tools/perf/tests/builtin-test.c:418:9
    linux-sunxi#17 0x559ceabbc4ab in test_and_print tools/perf/tests/builtin-test.c:448:9
    linux-sunxi#18 0x559ceabbac70 in __cmd_test tools/perf/tests/builtin-test.c:669:4
    linux-sunxi#19 0x559ceabbac70 in cmd_test tools/perf/tests/builtin-test.c:815:9
    linux-sunxi#20 0x559cea960e30 in run_builtin tools/perf/perf.c:313:11
    linux-sunxi#21 0x559cea95fbce in handle_internal_command tools/perf/perf.c:365:8
    linux-sunxi#22 0x559cea95fbce in run_argv tools/perf/perf.c:409:2
    linux-sunxi#23 0x559cea95fbce in main tools/perf/perf.c:539:3

  Uninitialized value was stored to memory at
    #0 0x559ceb106acf in __libdwfl_frame_reg_set elfutils/libdwfl/frame_unwind.c:77:22
    #1 0x559ceb106acf in handle_cfi elfutils/libdwfl/frame_unwind.c:627:13
    #2 0x559ceb105448 in __libdwfl_frame_unwind elfutils/libdwfl/frame_unwind.c:741:4
    #3 0x559ceb0ece90 in dwfl_thread_getframes elfutils/libdwfl/dwfl_frame.c:435:7
    #4 0x559ceb0ec6b7 in get_one_thread_frames_cb elfutils/libdwfl/dwfl_frame.c:379:10
    #5 0x559ceb0ec6b7 in get_one_thread_cb elfutils/libdwfl/dwfl_frame.c:308:17
    #6 0x559ceb0ec6b7 in dwfl_getthreads elfutils/libdwfl/dwfl_frame.c:283:17
    linux-sunxi#7 0x559ceb0ec6b7 in getthread elfutils/libdwfl/dwfl_frame.c:354:14
    linux-sunxi#8 0x559ceb0ec6b7 in dwfl_getthread_frames elfutils/libdwfl/dwfl_frame.c:388:10
    linux-sunxi#9 0x559ceaff6ae6 in unwind__get_entries tools/perf/util/unwind-libdw.c:236:8
    linux-sunxi#10 0x559ceabc9dbc in test_dwarf_unwind__thread tools/perf/tests/dwarf-unwind.c:111:8
    linux-sunxi#11 0x559ceabca5cf in test_dwarf_unwind__compare tools/perf/tests/dwarf-unwind.c:138:26
    linux-sunxi#12 0x7f812a6865b0 in bsearch (libc.so.6+0x4e5b0)
    linux-sunxi#13 0x559ceabca871 in test_dwarf_unwind__krava_3 tools/perf/tests/dwarf-unwind.c:162:2
    linux-sunxi#14 0x559ceabca926 in test_dwarf_unwind__krava_2 tools/perf/tests/dwarf-unwind.c:169:9
    linux-sunxi#15 0x559ceabca946 in test_dwarf_unwind__krava_1 tools/perf/tests/dwarf-unwind.c:174:9
    linux-sunxi#16 0x559ceabcae12 in test__dwarf_unwind tools/perf/tests/dwarf-unwind.c:211:8
    linux-sunxi#17 0x559ceabbc4ab in run_test tools/perf/tests/builtin-test.c:418:9
    linux-sunxi#18 0x559ceabbc4ab in test_and_print tools/perf/tests/builtin-test.c:448:9
    linux-sunxi#19 0x559ceabbac70 in __cmd_test tools/perf/tests/builtin-test.c:669:4
    linux-sunxi#20 0x559ceabbac70 in cmd_test tools/perf/tests/builtin-test.c:815:9
    linux-sunxi#21 0x559cea960e30 in run_builtin tools/perf/perf.c:313:11
    linux-sunxi#22 0x559cea95fbce in handle_internal_command tools/perf/perf.c:365:8
    linux-sunxi#23 0x559cea95fbce in run_argv tools/perf/perf.c:409:2
    linux-sunxi#24 0x559cea95fbce in main tools/perf/perf.c:539:3

  Uninitialized value was stored to memory at
    #0 0x559ceb106a54 in handle_cfi elfutils/libdwfl/frame_unwind.c:613:9
    #1 0x559ceb105448 in __libdwfl_frame_unwind elfutils/libdwfl/frame_unwind.c:741:4
    #2 0x559ceb0ece90 in dwfl_thread_getframes elfutils/libdwfl/dwfl_frame.c:435:7
    #3 0x559ceb0ec6b7 in get_one_thread_frames_cb elfutils/libdwfl/dwfl_frame.c:379:10
    #4 0x559ceb0ec6b7 in get_one_thread_cb elfutils/libdwfl/dwfl_frame.c:308:17
    #5 0x559ceb0ec6b7 in dwfl_getthreads elfutils/libdwfl/dwfl_frame.c:283:17
    #6 0x559ceb0ec6b7 in getthread elfutils/libdwfl/dwfl_frame.c:354:14
    linux-sunxi#7 0x559ceb0ec6b7 in dwfl_getthread_frames elfutils/libdwfl/dwfl_frame.c:388:10
    linux-sunxi#8 0x559ceaff6ae6 in unwind__get_entries tools/perf/util/unwind-libdw.c:236:8
    linux-sunxi#9 0x559ceabc9dbc in test_dwarf_unwind__thread tools/perf/tests/dwarf-unwind.c:111:8
    linux-sunxi#10 0x559ceabca5cf in test_dwarf_unwind__compare tools/perf/tests/dwarf-unwind.c:138:26
    linux-sunxi#11 0x7f812a6865b0 in bsearch (libc.so.6+0x4e5b0)
    linux-sunxi#12 0x559ceabca871 in test_dwarf_unwind__krava_3 tools/perf/tests/dwarf-unwind.c:162:2
    linux-sunxi#13 0x559ceabca926 in test_dwarf_unwind__krava_2 tools/perf/tests/dwarf-unwind.c:169:9
    linux-sunxi#14 0x559ceabca946 in test_dwarf_unwind__krava_1 tools/perf/tests/dwarf-unwind.c:174:9
    linux-sunxi#15 0x559ceabcae12 in test__dwarf_unwind tools/perf/tests/dwarf-unwind.c:211:8
    linux-sunxi#16 0x559ceabbc4ab in run_test tools/perf/tests/builtin-test.c:418:9
    linux-sunxi#17 0x559ceabbc4ab in test_and_print tools/perf/tests/builtin-test.c:448:9
    linux-sunxi#18 0x559ceabbac70 in __cmd_test tools/perf/tests/builtin-test.c:669:4
    linux-sunxi#19 0x559ceabbac70 in cmd_test tools/perf/tests/builtin-test.c:815:9
    linux-sunxi#20 0x559cea960e30 in run_builtin tools/perf/perf.c:313:11
    linux-sunxi#21 0x559cea95fbce in handle_internal_command tools/perf/perf.c:365:8
    linux-sunxi#22 0x559cea95fbce in run_argv tools/perf/perf.c:409:2
    linux-sunxi#23 0x559cea95fbce in main tools/perf/perf.c:539:3

  Uninitialized value was stored to memory at
    #0 0x559ceaff8800 in memory_read tools/perf/util/unwind-libdw.c:156:10
    #1 0x559ceb10f053 in expr_eval elfutils/libdwfl/frame_unwind.c:501:13
    #2 0x559ceb1060cc in handle_cfi elfutils/libdwfl/frame_unwind.c:603:18
    #3 0x559ceb105448 in __libdwfl_frame_unwind elfutils/libdwfl/frame_unwind.c:741:4
    #4 0x559ceb0ece90 in dwfl_thread_getframes elfutils/libdwfl/dwfl_frame.c:435:7
    #5 0x559ceb0ec6b7 in get_one_thread_frames_cb elfutils/libdwfl/dwfl_frame.c:379:10
    #6 0x559ceb0ec6b7 in get_one_thread_cb elfutils/libdwfl/dwfl_frame.c:308:17
    linux-sunxi#7 0x559ceb0ec6b7 in dwfl_getthreads elfutils/libdwfl/dwfl_frame.c:283:17
    linux-sunxi#8 0x559ceb0ec6b7 in getthread elfutils/libdwfl/dwfl_frame.c:354:14
    linux-sunxi#9 0x559ceb0ec6b7 in dwfl_getthread_frames elfutils/libdwfl/dwfl_frame.c:388:10
    linux-sunxi#10 0x559ceaff6ae6 in unwind__get_entries tools/perf/util/unwind-libdw.c:236:8
    linux-sunxi#11 0x559ceabc9dbc in test_dwarf_unwind__thread tools/perf/tests/dwarf-unwind.c:111:8
    linux-sunxi#12 0x559ceabca5cf in test_dwarf_unwind__compare tools/perf/tests/dwarf-unwind.c:138:26
    linux-sunxi#13 0x7f812a6865b0 in bsearch (libc.so.6+0x4e5b0)
    linux-sunxi#14 0x559ceabca871 in test_dwarf_unwind__krava_3 tools/perf/tests/dwarf-unwind.c:162:2
    linux-sunxi#15 0x559ceabca926 in test_dwarf_unwind__krava_2 tools/perf/tests/dwarf-unwind.c:169:9
    linux-sunxi#16 0x559ceabca946 in test_dwarf_unwind__krava_1 tools/perf/tests/dwarf-unwind.c:174:9
    linux-sunxi#17 0x559ceabcae12 in test__dwarf_unwind tools/perf/tests/dwarf-unwind.c:211:8
    linux-sunxi#18 0x559ceabbc4ab in run_test tools/perf/tests/builtin-test.c:418:9
    linux-sunxi#19 0x559ceabbc4ab in test_and_print tools/perf/tests/builtin-test.c:448:9
    linux-sunxi#20 0x559ceabbac70 in __cmd_test tools/perf/tests/builtin-test.c:669:4
    linux-sunxi#21 0x559ceabbac70 in cmd_test tools/perf/tests/builtin-test.c:815:9
    linux-sunxi#22 0x559cea960e30 in run_builtin tools/perf/perf.c:313:11
    linux-sunxi#23 0x559cea95fbce in handle_internal_command tools/perf/perf.c:365:8
    linux-sunxi#24 0x559cea95fbce in run_argv tools/perf/perf.c:409:2
    linux-sunxi#25 0x559cea95fbce in main tools/perf/perf.c:539:3

  Uninitialized value was stored to memory at
    #0 0x559cea9027d9 in __msan_memcpy llvm/llvm-project/compiler-rt/lib/msan/msan_interceptors.cpp:1558:3
    #1 0x559cea9d2185 in sample_ustack tools/perf/arch/x86/tests/dwarf-unwind.c:41:2
    #2 0x559cea9d202c in test__arch_unwind_sample tools/perf/arch/x86/tests/dwarf-unwind.c:72:9
    #3 0x559ceabc9cbd in test_dwarf_unwind__thread tools/perf/tests/dwarf-unwind.c:106:6
    #4 0x559ceabca5cf in test_dwarf_unwind__compare tools/perf/tests/dwarf-unwind.c:138:26
    #5 0x7f812a6865b0 in bsearch (libc.so.6+0x4e5b0)
    #6 0x559ceabca871 in test_dwarf_unwind__krava_3 tools/perf/tests/dwarf-unwind.c:162:2
    linux-sunxi#7 0x559ceabca926 in test_dwarf_unwind__krava_2 tools/perf/tests/dwarf-unwind.c:169:9
    linux-sunxi#8 0x559ceabca946 in test_dwarf_unwind__krava_1 tools/perf/tests/dwarf-unwind.c:174:9
    linux-sunxi#9 0x559ceabcae12 in test__dwarf_unwind tools/perf/tests/dwarf-unwind.c:211:8
    linux-sunxi#10 0x559ceabbc4ab in run_test tools/perf/tests/builtin-test.c:418:9
    linux-sunxi#11 0x559ceabbc4ab in test_and_print tools/perf/tests/builtin-test.c:448:9
    linux-sunxi#12 0x559ceabbac70 in __cmd_test tools/perf/tests/builtin-test.c:669:4
    linux-sunxi#13 0x559ceabbac70 in cmd_test tools/perf/tests/builtin-test.c:815:9
    linux-sunxi#14 0x559cea960e30 in run_builtin tools/perf/perf.c:313:11
    linux-sunxi#15 0x559cea95fbce in handle_internal_command tools/perf/perf.c:365:8
    linux-sunxi#16 0x559cea95fbce in run_argv tools/perf/perf.c:409:2
    linux-sunxi#17 0x559cea95fbce in main tools/perf/perf.c:539:3

  Uninitialized value was created by an allocation of 'bf' in the stack frame of function 'perf_event__synthesize_mmap_events'
    #0 0x559ceafc5f60 in perf_event__synthesize_mmap_events tools/perf/util/synthetic-events.c:445

SUMMARY: MemorySanitizer: use-of-uninitialized-value elfutils/libdwfl/frame_unwind.c:648:8 in handle_cfi
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: clang-built-linux@googlegroups.com
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandeep Dasgupta <sdasgup@google.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201113182053.754625-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/x86/tests/dwarf-unwind.c

@@ -38,6 +38,13 @@ static int sample_ustack(struct perf_sample *sample,
 	stack_size = stack_size > STACK_SIZE ? STACK_SIZE : stack_size;
 
 	memcpy(buf, (void *) sp, stack_size);
+#ifdef MEMORY_SANITIZER
+	/*
+	 * Copying the stack may copy msan poison, avoid false positives in the
+	 * unwinder by removing the poison here.
+	 */
+	__msan_unpoison(buf, stack_size);
+#endif
 	stack->data = (char *) buf;
 	stack->size = stack_size;
 	return 0;