perf test: Initialize memory in dwarf-unwind

Avoid a false positive caused by assembly code in arch/x86.

In tests, zero the perf_event to avoid uninitialized memory uses.

Warnings were caught using clang with -fsanitize=memory.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>
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: Quentin Monnet <quentin@isovalent.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: clang-built-linux@googlegroups.com
Link: http://lore.kernel.org/lkml/20200530082015.39162-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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

@@ -55,6 +55,14 @@ int test__arch_unwind_sample(struct perf_sample *sample,
 		return -1;
 	}
 
+#ifdef MEMORY_SANITIZER
+	/*
+	 * Assignments to buf in the assembly function perf_regs_load aren't
+	 * seen by memory sanitizer. Zero the memory to convince memory
+	 * sanitizer the memory is initialized.
+	 */
+	memset(buf, 0, sizeof(u64) * PERF_REGS_MAX);
+#endif
 	perf_regs_load(buf);
 	regs->abi  = PERF_SAMPLE_REGS_ABI;
 	regs->regs = buf;

tools/perf/tests/dwarf-unwind.c

@@ -37,6 +37,7 @@ static int init_live_machine(struct machine *machine)
 	union perf_event event;
 	pid_t pid = getpid();
 
+	memset(&event, 0, sizeof(event));
 	return perf_event__synthesize_mmap_events(NULL, &event, pid, pid,
 						  mmap_handler, machine, true);
 }