Re: [PATCH v3 next 04/17] selftests/nolibc: Improve reporting of vfprintf() errors

[David Laight]

On Wed, 25 Feb 2026 22:56:03 +0100
Thomas Weißschuh <linux@xxxxxxxxxxxxxx> wrote:

... 
> > Increase the size limit from 20 to 25 characters, changing the tests to
> > match. This is needed to test octal conversions later on.  
> 
> Then please do this right before the addition of the octal conversion.

I also kept hitting the limit trying to write other tests.
It is very easy to hit 20 chars when testing precision (three %6.2d is
too long)
Although I think the tests were written with that change done later.
I put it early so that I wouldn't have to change new tests that
tested truncation.

Perhaps I should justify the change because it lets tests check
longer data, not just octal?
I will then use longer test output in some of the other patches.

> 
> > Append a '+' to the printed output (after the final ") when the output
> > is truncated.
> > 
> > Additionally check that nothing beyond the end is written.
> > The "width_trunc" test (#14) now fails because e90ce42e81381
> > ("tools/nolibc: implement width padding in printf()") doesn't
> > correctly update the space in the buffer when adding pad characters.
> > This will be addressed in a later patch.  
> 
> The build bots will yell at us for this.
> Instead mark the test as skipped until it is fixed.

The build bots won't bleat - it is a run-time error.
But I can disable it.
I'm not sure there is a #define for 'broken' and there isn't
room for comments on the test cases.
So it might just be a literal 0.

> 
> > Also correctly return 1 (the number of errors) when strcmp()
> > fails rather than the return value from strncmp() which is the
> > signed difference between the mismatching characters.  
> 
> Please split these different steps into dedicated commits.
> Yes, the testcases are going to be rewritten a bunch of times,
> but that does not matter.
> 
> > Signed-off-by: David Laight <david.laight.linux@xxxxxxxxx>
> > ---
> > 
> > For v3:
> > - Patch 9 in v2, patch 5 in v1..
> > - Increase the size limit to 25 in preparation for testing octal.
> > - Change the way truncated fprintf() are handled.
> > - Allow for tests being skipped.
> > - Use a fixed value (0xa5) for the canary when detecting overwrites.
> > 
> >  tools/testing/selftests/nolibc/nolibc-test.c | 91 ++++++++++++++------
> >  1 file changed, 64 insertions(+), 27 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> > index 0e8b3b9a86ef..029ed63e1ae4 100644
> > --- a/tools/testing/selftests/nolibc/nolibc-test.c
> > +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> > @@ -1660,33 +1660,70 @@ int run_stdlib(int min, int max)
> >  	return ret;
> >  }
> >  
> > -#define EXPECT_VFPRINTF(c, expected, fmt, ...)				\
> > -	ret += expect_vfprintf(llen, c, expected, fmt, ##__VA_ARGS__)
> > +#define EXPECT_VFPRINTF(cond, expected, fmt, ...)				\
> > +	ret += expect_vfprintf(llen, cond, expected, fmt, ##__VA_ARGS__)
> >  
> > -static int expect_vfprintf(int llen, int c, const char *expected, const char *fmt, ...)
> > +#define VFPRINTF_LEN 25  
> 
> This is only used within expect_vfprintf(), so it can be a local variable.

I used it to size buf[] so it needs to be an 'integer constant expression'.
The only simple way to do that is with a #define - which isn't scoped.

> 
> > +
> > +static int expect_vfprintf(int llen, int cond, const char *expected, const char *fmt, ...)
> >  {
> > -	char buf[100];
> > +	ssize_t written, expected_len;
> > +	char buf[VFPRINTF_LEN + 80];
> > +	unsigned int cmp_len;
> >  	va_list args;
> > -	ssize_t w;
> > -	int ret;
> >  
> > +	if (!cond) {
> > +		result(llen, SKIPPED);
> > +		return 0;
> > +	}  
> 
> The other EXPECT_*() macros evaluate the condition in the macro, not the
> corresponding function. I'm not entirely sure why that is, but please
> keep it consistent.

Most of the other ones call the function in the #define and just report
the success/fail in the function. The SKIP test has to be before the
function call - so has to be in the #define.
For vfprintf (should be snprintf) the test is in the function.
So really it should be TEST_SNPRINTF().
The only other similar one is EXPECT_STRTOX().

But I can change it for consistency.

I might just re-post patches to this file.

The later patches will depend on it, but that won't matter if it
get applied.

Where do these patches get applied to?
So I can base new versions on the changes.
I guess they'll get picked up into 'next' fairly quickly.

	David