[PATCH] lib/test_printf.c: fix clang -Wformat warnings

[Justin Stitt]

see warnings:
| lib/test_printf.c:157:52: error: format specifies type 'unsigned char'
| but the argument has type 'int' [-Werror,-Wformat] test("0|1|1|128|255",
| "%hhu|%hhu|%hhu|%hhu|%hhu", 0, 1, 257, 128, -1);
-
| lib/test_printf.c:158:55: error: format specifies type 'char' but the
| argument has type 'int' [-Werror,-Wformat] test("0|1|1|-128|-1",
| "%hhd|%hhd|%hhd|%hhd|%hhd", 0, 1, 257, 128, -1);
-
| lib/test_printf.c:159:41: error: format specifies type 'unsigned short'
| but the argument has type 'int' [-Werror,-Wformat]
| test("2015122420151225", "%ho%ho%#ho", 1037, 5282, -11627);

There's an ongoing movement to eventually enable the -Wformat flag for
clang. Previous patches have targeted incorrect usage of
format specifiers. In this case, however, the "incorrect" format
specifiers are intrinsically part of the test cases. Hence, fixing them
would be misaligned with their intended purpose. My proposed fix is to
simply disable the warnings so that one day a clean build of the kernel
with clang (and -Wformat enabled) would be possible. It would also keep
us in the green for alot of the CI bots.

Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
---
 lib/test_printf.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 07309c45f327..748591a0c55c 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -4,6 +4,12 @@
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#define DO_PRAGMA(x) _Pragma(#x)
+#define NOWARN(warnoption, ...)
+	    DO_PRAGMA(GCC diagnostic push)
+		    DO_PRAGMA(GCC diagnostic ignored #warnoption)
+			    __VA_ARGS__
+				    DO_PRAGMA(GCC diagnostic pop)
 
 #include <linux/init.h>
 #include <linux/kernel.h>
@@ -154,9 +160,13 @@ test_number(void)
 	test("0x1234abcd  ", "%#-12x", 0x1234abcd);
 	test("  0x1234abcd", "%#12x", 0x1234abcd);
 	test("0|001| 12|+123| 1234|-123|-1234", "%d|%03d|%3d|%+d|% d|%+d|% d", 0, 1, 12, 123, 1234, -123, -1234);
+	/* disable -Wformat for this chunk */
+	NOWARN(-Wformat, 
 	test("0|1|1|128|255", "%hhu|%hhu|%hhu|%hhu|%hhu", 0, 1, 257, 128, -1);
 	test("0|1|1|-128|-1", "%hhd|%hhd|%hhd|%hhd|%hhd", 0, 1, 257, 128, -1);
 	test("2015122420151225", "%ho%ho%#ho", 1037, 5282, -11627);
+	)
+	/* end chunk */
 	/*
 	 * POSIX/C99: »The result of converting zero with an explicit
 	 * precision of zero shall be no characters.« Hence the output
-- 
2.37.0.rc0.161.g10f37bed90-goog