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From:   Daniel Latypov <dlatypov@google.com>
Date:   Thu, 13 May 2021 13:25:35 -0700
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Subject: Re: [PATCH] kunit: Add gnu_printf specifiers
To:     David Gow <davidgow@google.com>
Cc:     Brendan Higgins <brendanhiggins@google.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        KUnit Development <kunit-dev@googlegroups.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, May 13, 2021 at 1:03 PM 'David Gow' via KUnit Development
<kunit-dev@googlegroups.com> wrote:
>
> Some KUnit functions use variable arguments to implement a printf-like
> format string. Use the __printf() attribute to let the compiler warn if
> invalid format strings are passed in.
>
> If the kernel is build with W=3D1, it complained about the lack of these
> specifiers, e.g.:
> ../lib/kunit/test.c:72:2: warning: function =E2=80=98kunit_log_append=E2=
=80=99 might be a candidate for =E2=80=98gnu_printf=E2=80=99 format attribu=
te [-Wsuggest-attribute=3Dformat]
>
> Signed-off-by: David Gow <davidgow@google.com>

Reviewed-by: Daniel Latypov <dlatypov@google.com>

As noted below, these additions don't really do anything.
Unfortunately, they just make compiler warnings noisier in the case of
kunit_log_append().

But if this silences a W=3D1 warning, then we should probably add them in.
I guess it also serves as documentation that we're using the same
standard format specifiers and not something custom, which is nice.

> ---
>  include/kunit/test.h      | 2 +-
>  lib/kunit/string-stream.h | 6 +++---
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/kunit/test.h b/include/kunit/test.h
> index 49601c4b98b8..af2e386b867c 100644
> --- a/include/kunit/test.h
> +++ b/include/kunit/test.h
> @@ -610,7 +610,7 @@ static inline void *kunit_kzalloc(struct kunit *test,=
 size_t size, gfp_t gfp)
>
>  void kunit_cleanup(struct kunit *test);
>
> -void kunit_log_append(char *log, const char *fmt, ...);
> +void __printf(2, 3) kunit_log_append(char *log, const char *fmt, ...);

Before this patch:
../lib/kunit/kunit-example-test.c: In function =E2=80=98example_simple_test=
=E2=80=99:
../include/linux/kern_levels.h:5:18: warning: format =E2=80=98%s=E2=80=99 e=
xpects
argument of type =E2=80=98char *=E2=80=99, but argument 3 has type =E2=80=
=98int=E2=80=99 [-Wformat=3D]
    5 | #define KERN_SOH "\001"  /* ASCII Start Of Header */
      |                  ^~~~~~
../include/kunit/test.h:622:10: note: in definition of macro =E2=80=98kunit=
_log=E2=80=99
  622 |   printk(lvl fmt, ##__VA_ARGS__);    \
      |          ^~~
../include/kunit/test.h:641:2: note: in expansion of macro =E2=80=98kunit_p=
rintk=E2=80=99
  641 |  kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
      |  ^~~~~~~~~~~~
../include/linux/kern_levels.h:14:19: note: in expansion of macro =E2=80=98=
KERN_SOH=E2=80=99
   14 | #define KERN_INFO KERN_SOH "6" /* informational */
      |                   ^~~~~~~~
../include/kunit/test.h:641:15: note: in expansion of macro =E2=80=98KERN_I=
NFO=E2=80=99
  641 |  kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
      |               ^~~~~~~~~
../lib/kunit/kunit-example-test.c:23:2: note: in expansion of macro =E2=80=
=98kunit_info=E2=80=99
   23 |  kunit_info(test, "invalid: %s", 42);

After this patch, it gets noisier:
In file included from ../lib/kunit/kunit-example-test.c:9:
../lib/kunit/kunit-example-test.c: In function =E2=80=98example_simple_test=
=E2=80=99:
../include/linux/kern_levels.h:5:18: warning: format =E2=80=98%s=E2=80=99 e=
xpects
argument of type =E2=80=98char *=E2=80=99, but argument 3 has type =E2=80=
=98int=E2=80=99 [-Wformat=3D]
    5 | #define KERN_SOH "\001"  /* ASCII Start Of Header */
      |                  ^~~~~~
../include/kunit/test.h:622:10: note: in definition of macro =E2=80=98kunit=
_log=E2=80=99
  622 |   printk(lvl fmt, ##__VA_ARGS__);    \
      |          ^~~
../include/kunit/test.h:641:2: note: in expansion of macro =E2=80=98kunit_p=
rintk=E2=80=99
  641 |  kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
      |  ^~~~~~~~~~~~
../include/linux/kern_levels.h:14:19: note: in expansion of macro =E2=80=98=
KERN_SOH=E2=80=99
   14 | #define KERN_INFO KERN_SOH "6" /* informational */
      |                   ^~~~~~~~
../include/kunit/test.h:641:15: note: in expansion of macro =E2=80=98KERN_I=
NFO=E2=80=99
  641 |  kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
      |               ^~~~~~~~~
../lib/kunit/kunit-example-test.c:23:2: note: in expansion of macro =E2=80=
=98kunit_info=E2=80=99
   23 |  kunit_info(test, "invalid: %s", 42);
      |  ^~~~~~~~~~
../include/kunit/test.h:105:31: warning: format =E2=80=98%s=E2=80=99 expect=
s argument
of type =E2=80=98char *=E2=80=99, but argument 4 has type =E2=80=98int=E2=
=80=99 [-Wformat=3D]
  105 | #define KUNIT_SUBTEST_INDENT  "    "
      |                               ^~~~~~
../include/kunit/test.h:623:42: note: in definition of macro =E2=80=98kunit=
_log=E2=80=99
  623 |   kunit_log_append((test_or_suite)->log, fmt "\n", \
      |                                          ^~~
../include/kunit/test.h:628:23: note: in expansion of macro
=E2=80=98KUNIT_SUBTEST_INDENT=E2=80=99
  628 |  kunit_log(lvl, test, KUNIT_SUBTEST_INDENT "# %s: " fmt,  \
      |                       ^~~~~~~~~~~~~~~~~~~~
../include/kunit/test.h:641:2: note: in expansion of macro =E2=80=98kunit_p=
rintk=E2=80=99
  641 |  kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
      |  ^~~~~~~~~~~~
../lib/kunit/kunit-example-test.c:23:2: note: in expansion of macro =E2=80=
=98kunit_info=E2=80=99
   23 |  kunit_info(test, "invalid: %s", 42);
      |  ^~~~~~~~~~


>
>  /*
>   * printk and log to per-test or per-suite log buffer.  Logging only don=
e
> diff --git a/lib/kunit/string-stream.h b/lib/kunit/string-stream.h
> index fe98a00b75a9..5e94b623454f 100644
> --- a/lib/kunit/string-stream.h
> +++ b/lib/kunit/string-stream.h
> @@ -35,9 +35,9 @@ struct string_stream *alloc_string_stream(struct kunit =
*test, gfp_t gfp);
>  int __printf(2, 3) string_stream_add(struct string_stream *stream,
>                                      const char *fmt, ...);
>
> -int string_stream_vadd(struct string_stream *stream,
> -                      const char *fmt,
> -                      va_list args);
> +int __printf(2, 0) string_stream_vadd(struct string_stream *stream,
> +                                     const char *fmt,
> +                                     va_list args);

This is never called with a literal `fmt` string.
It's currently only ever called through the _add variant, which does
have __printf(2,3).

So this can't catch any mistakes currently.
And I think it's hard to imagine we'd ever pass in a literal format
string w/ a va_list.

>
>  char *string_stream_get_string(struct string_stream *stream);
>
> --
> 2.31.1.751.gd2f1c929bd-goog
>
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