[PATCH AUTOSEL 4.9 11/20] perf data: Fix 'strncat may truncate' build failure with recent gcc

[Sasha Levin]

From: Shawn Landden <shawn@xxxxxxx>

[ Upstream commit 97acec7df172cd1e450f81f5e293c0aa145a2797 ]

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 âstrncatâ,
      inlined from âstring_set_valueâ at util/data-convert-bt.c:274:4:
  /usr/include/powerpc64le-linux-gnu/bits/string_fortified.h:136:10: error: â__builtin_strncatâ 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));
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Shawn Landden <shawn@xxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
LPU-Reference: 20190518183238.10954-1-shawn@xxxxxxx
Link: https://lkml.kernel.org/n/tip-289f1jice17ta7tr3tstm9jm@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/perf/util/data-convert-bt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/data-convert-bt.c b/tools/perf/util/data-convert-bt.c
index 7123f4de32cc..226f4312b8f3 100644
--- a/tools/perf/util/data-convert-bt.c
+++ b/tools/perf/util/data-convert-bt.c
@@ -265,7 +265,7 @@ 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;
 		}
 	}
-- 
2.20.1