perf data: Fix 'strncat may truncate' build failure with recent gcc

Commit-ID:  97acec7df172cd1e450f81f5e293c0aa145a2797
Gitweb:     https://git.kernel.org/tip/97acec7df172cd1e450f81f5e293c0aa145a2797
Author:     Shawn Landden <[email protected]>
AuthorDate: Sat, 18 May 2019 15:32:38 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Tue, 28 May 2019 09:49:03 -0300

perf data: Fix 'strncat may truncate' build failure with recent gcc

This strncat() is safe because the buffer was allocated with zalloc(), however gcc doesn't know that. Since the string always has 4 non-null bytes, just use memcpy() here.

CC /home/shawn/linux/tools/perf/util/data-convert-bt.o
In file included from /usr/include/string.h:494,

                   from /home/shawn/linux/tools/lib/traceevent/event-parse.h:27,
                   from util/data-convert-bt.c:22:
  In function ‘strncat’,
      inlined from ‘string_set_value’ at util/data-convert-bt.c:274:4:
  /usr/include/powerpc64le-linux-gnu/bits/string_fortified.h:136:10: error: ‘__builtin_strncat’ output may be truncated copying 4 bytes from a string of length 4 [-Werror=stringop-truncation]
    136 |   return __builtin___strncat_chk (__dest, __src, __len, __bos (__dest));
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

LPU-Reference: [email protected]

---
 tools/perf/util/data-convert-bt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index e0311c9750ad..9097543a818b 100644
@@ -271,7 +271,7 @@ static int string_set_value(struct bt_ctf_field *field, const char *string)
 				if (i > 0)
 					strncpy(buffer, string, i);
 			}
-			strncat(buffer + p, numstr, 4);
+			memcpy(buffer + p, numstr, 4);
 			p += 3;
 		}
 	}