perf ui helpline: Use strlcpy() as a shorter form of strncpy() + expl…

…icit set nul

commit 4d0f16d059ddb91424480d88473f7392f24aebdc upstream.

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

In this case we are actually setting the null byte at the right place,
but since we pass the buffer size as the limit to strncpy() and not
it minus one, gcc ends up warning us about that, see below. So, lets
just switch to the shorter form provided by strlcpy().

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

  ui/tui/helpline.c: In function 'tui_helpline__push':
  ui/tui/helpline.c:27:2: error: 'strncpy' specified bound 512 equals destination size [-Werror=stringop-truncation]
    strncpy(ui_helpline__current, msg, sz)[sz - 1] = '\0';
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

Cc: Adrian Hunter <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Fixes: e6e9046 ("perf ui: Introduce struct ui_helpline")
Link: https://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

tools/perf/ui/tui/helpline.c

@@ -24,7 +24,7 @@ static void tui_helpline__push(const char *msg)
 	SLsmg_set_color(0);
 	SLsmg_write_nstring((char *)msg, SLtt_Screen_Cols);
 	SLsmg_refresh();
-	strncpy(ui_helpline__current, msg, sz)[sz - 1] = '\0';
+	strlcpy(ui_helpline__current, msg, sz);
 }
 
 static int tui_helpline__show(const char *format, va_list ap)