lib/test_printf.c: test precision quirks

The kernel's printf doesn't follow the standards in a few corner cases
(which are probably mostly irrelevant).  Add tests that document the
current behaviour.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Maurizio Lombardi <mlombard@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 1ce1a1dd8faf4ee3748cf4d911598fe575b3f799..3393d667c6b8ae99cf8a3cd65fac086250edefe9 100644 (file)
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -166,14 +166,23 @@ test_string(void)
        test("", "%s%.0s", "", "123");
        test("ABCD|abc|123", "%s|%.3s|%.*s", "ABCD", "abcdef", 3, "123456");
        test("1  |  2|3  |  4|5  ", "%-3s|%3s|%-*s|%*s|%*s", "1", "2", 3, "3", 3, "4", -3, "5");
+       test("1234      ", "%-10.4s", "123456");
+       test("      1234", "%10.4s", "123456");
        /*
-        * POSIX and C99 say that a missing precision should be
-        * treated as a precision of 0. However, the kernel's printf
-        * implementation treats this case as if the . wasn't
-        * present. Let's add a test case documenting the current
-        * behaviour; should anyone ever feel the need to follow the
-        * standards more closely, this can be revisited.
+        * POSIX and C99 say that a negative precision (which is only
+        * possible to pass via a * argument) should be treated as if
+        * the precision wasn't present, and that if the precision is
+        * omitted (as in %.s), the precision should be taken to be
+        * 0. However, the kernel's printf behave exactly opposite,
+        * treating a negative precision as 0 and treating an omitted
+        * precision specifier as if no precision was given.
+        *
+        * These test cases document the current behaviour; should
+        * anyone ever feel the need to follow the standards more
+        * closely, this can be revisited.
         */
+       test("    ", "%4.*s", -5, "123456");
+       test("123456", "%.s", "123456");
        test("a||", "%.s|%.0s|%.*s", "a", "b", 0, "c");
        test("a  |   |   ", "%-3.s|%-3.0s|%-3.*s", "a", "b", 0, "c");
 }