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

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Message-ID: <f3e97a68-71fe-c077-5add-a6c0fb397032@opensource.cirrus.com>
Date:   Tue, 15 Dec 2020 14:26:53 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Petr Mladek <pmladek@...e.com>
CC:     <rostedt@...dmis.org>, <sergey.senozhatsky@...il.com>,
        <shuah@...nel.org>, <patches@...nsource.cirrus.com>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] lib: test_scanf: Add tests for sscanf number
 conversion



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
>