[PATCH v1] perf string: Avoid undefined NULL+1

[Ian Rogers <irogers@google.com>]

While the value NULL+1 is never used it triggers a ubsan
warning. Restructure and comment the loop to avoid this.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/string.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/string.c b/tools/perf/util/string.c
index 308fc7ec88cc..c0e927bbadf6 100644
--- a/tools/perf/util/string.c
+++ b/tools/perf/util/string.c
@@ -254,11 +254,20 @@ char *strpbrk_esc(char *str, const char *stopset)
 
 	do {
 		ptr = strpbrk(str, stopset);
-		if (ptr == str ||
-		    (ptr == str + 1 && *(ptr - 1) != '\\'))
+		if (!ptr) {
+			/* stopset not in str. */
 			break;
+		}
+		if (ptr == str) {
+			/* stopset character is first in str. */
+			break;
+		}
+		if (ptr == str + 1 && str[0] != '\\') {
+			/* stopset chacter is second and wasn't preceded by a '\'. */
+			break;
+		}
 		str = ptr + 1;
-	} while (ptr && *(ptr - 1) == '\\' && *(ptr - 2) != '\\');
+	} while (ptr[-1] == '\\' && ptr[-2] != '\\');
 
 	return ptr;
 }
-- 
2.47.0.371.ga323438b13-goog