perf header: Fix unchecked usage of strncpy()

The strncpy() function may leave the destination string buffer
unterminated, better use strlcpy() that we have a __weak fallback
implementation for systems without it.

This fixes this warning on an Alpine Linux Edge system with gcc 8.2:

  util/header.c: In function 'perf_event__synthesize_event_update_unit':
  util/header.c:3586:2: error: 'strncpy' output truncated before terminating nul copying as many bytes from a string as its length [-Werror=stringop-truncation]
    strncpy(ev->data, evsel->unit, size);
  util/header.c:3579:16: note: length computed here
    size_t size = strlen(evsel->unit);

Cc: Adrian Hunter <>
Cc: Jiri Olsa <>
Cc: Namhyung Kim <>
Fixes: a6e52817 ("perf tools: Add event_update event unit type")
Link: 's avatarArnaldo Carvalho de Melo <>
parent fca5085c
......@@ -3583,7 +3583,7 @@ perf_event__synthesize_event_update_unit(struct perf_tool *tool,
if (ev == NULL)
return -ENOMEM;
strncpy(ev->data, evsel->unit, size);
strlcpy(ev->data, evsel->unit, size + 1);
err = process(tool, (union perf_event *)ev, NULL, NULL);
return err;
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