Re: [PATCH v2 2/4] lib: test_scanf: Add tests for sscanf number conversion

[Richard Fitzgerald]

On 09/12/2020 14:15, Petr Mladek wrote:
> On Mon 2020-11-30 14:57:58, Richard Fitzgerald wrote:
> > Adds test_sscanf to test various number conversion cases, as
> > number conversion was previously broken.
> >
> > This also tests the simple_strtoxxx() functions exported from
> > vsprintf.c.
>
> It is impressive.
>
> Honestly, I do not feel to be expert on testing and mathematics.
> I am not sure how comprehensive the test is. Also I am not
> sure what experts would say about the tricks with random
> numbers.
>
> Anyway, this is much more than what I have expected. And it checks
> great number of variants and corner cases.
>
> I suggest only one small change, see below.
>
> > --- /dev/null
> > +++ b/lib/test_scanf.c
> > @@ -0,0 +1,747 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Test cases for sscanf facility.
> > + */
> > +
> > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> > +
> > +#include <linux/bitops.h>
> > +#include <linux/init.h>
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/overflow.h>
> > +#include <linux/printk.h>
> > +#include <linux/random.h>
> > +#include <linux/slab.h>
> > +#include <linux/string.h>
> > +
> > +#include "../tools/testing/selftests/kselftest_module.h"
> > +
> > +#define BUF_SIZE 1024
> > +
> > +static unsigned total_tests __initdata;
> > +static unsigned failed_tests __initdata;
> > +static char *test_buffer __initdata;
> > +static char *fmt_buffer __initdata;
> > +static struct rnd_state rnd_state __initdata;
> > +
> > +typedef int (*check_fn)(const void *check_data, const char *string,
> > +			const char *fmt, int n_args, va_list ap);
> > +
> > +static void __scanf(4, 6) __init
> > +_test(check_fn fn, const void *check_data, const char *string, const char *fmt,
> > +	int n_args, ...)
> > +{
> > +	va_list ap, ap_copy;
> > +	int ret;
> > +
> > +	total_tests++;
> > +
> > +	va_start(ap, n_args);
> > +	va_copy(ap_copy, ap);
> > +	ret = vsscanf(string, fmt, ap_copy);
> > +	va_end(ap_copy);
> > +
> > +	if (ret != n_args) {
> > +		pr_warn("vsscanf(\"%s\", \"%s\", ...) returned %d expected %d\n",
> > +			string, fmt, ret, n_args);
> > +		goto fail;
> > +	}
> > +
> > +	ret = (*fn)(check_data, string, fmt, n_args, ap);
> > +	if (ret)
> > +		goto fail;
> > +
> > +	va_end(ap);
> > +
> > +	return;
> > +
> > +fail:
> > +	failed_tests++;
> > +	va_end(ap);
> > +}
> > +
> > +#define test_one_number(T, gen_fmt, scan_fmt, val, fn)			\
> > +do {									\
> > +	const T expect_val = (T)(val);					\
> > +	T result = ~expect_val; /* should be overwritten */		\
>
> If I get it correctly, this is supposed to initialize the temporary
> variable with a value that is different from the expected value.
> It will cause test failure when it is not updated by vsscanf().
>
> It does not work for zero value. A better solution might be to add

That's a ~, not a -
~0 = 0xFFFFFFFF
~-1 = 0

> a constant, for example:
>
> 	T result = expect_val + 3; /* do not match when not overwritten */ \
>
> I did not use "+ 1" intentionally because it might hide some overflow
> issues.
>
> > +									\
> > +	snprintf(test_buffer, BUF_SIZE, gen_fmt, expect_val);		\
> > +	_test(fn, &expect_val, test_buffer, "%" scan_fmt, 1, &result);	\
> > +} while (0)
>
> Otherwise, it looks good to me.
>
> Best Regards,
> Petr