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    Subject[PATCH 11/14] lib/test_printf.c: test precision quirks
    Date
    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.

    Cc: Kees Cook <keescook@chromium.org>
    Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
    ---
    lib/test_printf.c | 20 ++++++++++++++------
    1 file changed, 14 insertions(+), 6 deletions(-)

    diff --git a/lib/test_printf.c b/lib/test_printf.c
    index 1ce1a1dd8faf..5f742b99cfdc 100644
    --- a/lib/test_printf.c
    +++ b/lib/test_printf.c
    @@ -166,14 +166,22 @@ 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("a||", "%.s|%.0s|%.*s", "a", "b", 0, "c");
    test("a | | ", "%-3.s|%-3.0s|%-3.*s", "a", "b", 0, "c");
    }
    --
    2.6.1


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