Re: [PATCH] kunit: Add gnu_printf specifiers

From: Daniel Latypov
Date: Thu May 13 2021 - 16:25:51 EST

On Thu, May 13, 2021 at 1:03 PM 'David Gow' via KUnit Development
<kunit-dev@xxxxxxxxxxxxxxxx> 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=1, it complained about the lack of these
> specifiers, e.g.:
> ../lib/kunit/test.c:72:2: warning: function ‘kunit_log_append’ might be a candidate for ‘gnu_printf’ format attribute [-Wsuggest-attribute=format]
>
> Signed-off-by: David Gow <davidgow@xxxxxxxxxx>

Reviewed-by: Daniel Latypov <dlatypov@xxxxxxxxxx>

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=1 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 ‘example_simple_test’:
../include/linux/kern_levels.h:5:18: warning: format ‘%s’ expects
argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
5 | #define KERN_SOH "\001" /* ASCII Start Of Header */
| ^~~~~~
../include/kunit/test.h:622:10: note: in definition of macro ‘kunit_log’
622 | printk(lvl fmt, ##__VA_ARGS__); \
| ^~~
../include/kunit/test.h:641:2: note: in expansion of macro ‘kunit_printk’
641 | kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
| ^~~~~~~~~~~~
../include/linux/kern_levels.h:14:19: note: in expansion of macro ‘KERN_SOH’
14 | #define KERN_INFO KERN_SOH "6" /* informational */
| ^~~~~~~~
../include/kunit/test.h:641:15: note: in expansion of macro ‘KERN_INFO’
641 | kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
| ^~~~~~~~~
../lib/kunit/kunit-example-test.c:23:2: note: in expansion of macro ‘kunit_info’
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 ‘example_simple_test’:
../include/linux/kern_levels.h:5:18: warning: format ‘%s’ expects
argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
5 | #define KERN_SOH "\001" /* ASCII Start Of Header */
| ^~~~~~
../include/kunit/test.h:622:10: note: in definition of macro ‘kunit_log’
622 | printk(lvl fmt, ##__VA_ARGS__); \
| ^~~
../include/kunit/test.h:641:2: note: in expansion of macro ‘kunit_printk’
641 | kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
| ^~~~~~~~~~~~
../include/linux/kern_levels.h:14:19: note: in expansion of macro ‘KERN_SOH’
14 | #define KERN_INFO KERN_SOH "6" /* informational */
| ^~~~~~~~
../include/kunit/test.h:641:15: note: in expansion of macro ‘KERN_INFO’
641 | kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
| ^~~~~~~~~
../lib/kunit/kunit-example-test.c:23:2: note: in expansion of macro ‘kunit_info’
23 | kunit_info(test, "invalid: %s", 42);
| ^~~~~~~~~~
../include/kunit/test.h:105:31: warning: format ‘%s’ expects argument
of type ‘char *’, but argument 4 has type ‘int’ [-Wformat=]
105 | #define KUNIT_SUBTEST_INDENT " "
| ^~~~~~
../include/kunit/test.h:623:42: note: in definition of macro ‘kunit_log’
623 | kunit_log_append((test_or_suite)->log, fmt "\n", \
| ^~~
../include/kunit/test.h:628:23: note: in expansion of macro
‘KUNIT_SUBTEST_INDENT’
628 | kunit_log(lvl, test, KUNIT_SUBTEST_INDENT "# %s: " fmt, \
| ^~~~~~~~~~~~~~~~~~~~
../include/kunit/test.h:641:2: note: in expansion of macro ‘kunit_printk’
641 | kunit_printk(KERN_INFO, test, fmt, ##__VA_ARGS__)
| ^~~~~~~~~~~~
../lib/kunit/kunit-example-test.c:23:2: note: in expansion of macro ‘kunit_info’
23 | kunit_info(test, "invalid: %s", 42);
| ^~~~~~~~~~


>
> /*
> * printk and log to per-test or per-suite log buffer. Logging only done
> 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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