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[2/5] tools/nolibc/stdio: Add format attribute to enable printf warnings

Message ID 20220620231328.3845126-2-paulmck@kernel.org (mailing list archive)
State Mainlined
Commit 4f2c9703a128d21db7d0bf2ea14c5fe50d0dfe7e
Headers show
Series nolibc updates for v5.20 | expand

Commit Message

Paul E. McKenney June 20, 2022, 11:13 p.m. UTC 
From: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>

When we use printf and fprintf functions from the nolibc, we don't
get any warning from the compiler if we have the wrong arguments.
For example, the following calls will compile silently:
```
  printf("%s %s\n", "aaa");
  fprintf(stdout, "%s %s\n", "xxx", 1);
```
(Note the wrong arguments).

Those calls are undefined behavior. The compiler can help us warn
about the above mistakes by adding a `printf` format attribute to
those functions declaration. This patch adds it, and now it yields
these warnings for those mistakes:
```
  warning: format `%s` expects a matching `char *` argument [-Wformat=]
  warning: format `%s` expects argument of type `char *`, but argument 4 has type `int` [-Wformat=]
```

  [ ammarfaizi2: Simplify the attribute placement. ]

Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 tools/include/nolibc/stdio.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 15dedf8d0902d..a3cebc4bc3ac4 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -273,7 +273,7 @@  int vfprintf(FILE *stream, const char *fmt, va_list args)
 	return written;
 }
 
-static __attribute__((unused))
+static __attribute__((unused, format(printf, 2, 3)))
 int fprintf(FILE *stream, const char *fmt, ...)
 {
 	va_list args;
@@ -285,7 +285,7 @@  int fprintf(FILE *stream, const char *fmt, ...)
 	return ret;
 }
 
-static __attribute__((unused))
+static __attribute__((unused, format(printf, 1, 2)))
 int printf(const char *fmt, ...)
 {
 	va_list args;