coredump: add __printf attribute to cn_*printf functions

This allows detecting improper format string at build time, like:

  fs/coredump.c:225:5: warning: format '%ld' expects argument of type 'long int', but argument 3 has type 'int' [-Wformat=]
       err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
       ^

As si_signo is always an int, the format should be %d here.

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/coredump.c

@@ -70,7 +70,8 @@ static int expand_corename(struct core_name *cn, int size)
 	return 0;
 }
 
-static int cn_vprintf(struct core_name *cn, const char *fmt, va_list arg)
+static __printf(2, 0) int cn_vprintf(struct core_name *cn, const char *fmt,
+				     va_list arg)
 {
 	int free, need;
 	va_list arg_copy;
@@ -93,7 +94,7 @@ again:
 	return -ENOMEM;
 }
 
-static int cn_printf(struct core_name *cn, const char *fmt, ...)
+static __printf(2, 3) int cn_printf(struct core_name *cn, const char *fmt, ...)
 {
 	va_list arg;
 	int ret;
@@ -105,7 +106,8 @@ static int cn_printf(struct core_name *cn, const char *fmt, ...)
 	return ret;
 }
 
-static int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
+static __printf(2, 3)
+int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 {
 	int cur = cn->used;
 	va_list arg;
@@ -225,7 +227,8 @@ static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 				break;
 			/* signal that caused the coredump */
 			case 's':
-				err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
+				err = cn_printf(cn, "%d",
+						cprm->siginfo->si_signo);
 				break;
 			/* UNIX time of coredump */
 			case 't': {