linux-kernel - Re: [PATCH v15 1/6] x86/boot: Copy kstrtoull() to boot/string.c instead of using simple

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Message-ID: <20190109124853.GD15665@zn.tnic>
Date:   Wed, 9 Jan 2019 13:48:53 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, keescook@...omium.org,
        bhe@...hat.com, msys.mizuma@...il.com, indou.takao@...fujitsu.com,
        caoj.fnst@...fujitsu.com
Subject: Re: [PATCH v15 1/6] x86/boot: Copy kstrtoull() to boot/string.c
 instead of using simple_strtoull()

On Mon, Jan 07, 2019 at 11:22:38AM +0800, Chao Fan wrote:
> Copy kstrtoull() and necessary functions from lib/kstrtox.c to
> boot/string.c so that code in boot/ can use kstrtoull() and the old
> simple_strtoull() can be replaced.
> 
> In boot/string.c, using div_u64() from math64.h directly will cause the
> dividend handled as 64-bit value and bring ld error. The solution is to
> separate the dividend to upper and lower in boot/string.o. So copy the
> useful div_u64() and div_u64_rem() to boot/string.c also. To avoid
> redefinition in i386, rename them as __div_u64() and __div_u64_rem().
> 
> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
> ---
>  arch/x86/boot/string.c | 137 +++++++++++++++++++++++++++++++++++++++++
>  arch/x86/boot/string.h |   2 +
>  2 files changed, 139 insertions(+)

...

> +static inline char _tolower(const char c)
> +{
> +	return c | 0x20;
> +}
> +
> +const char *_parse_integer_fixup_radix(const char *s, unsigned int *base)

static

> +{
> +	if (*base == 0) {
> +		if (s[0] == '0') {
> +			if (_tolower(s[1]) == 'x' && isxdigit(s[2]))
> +				*base = 16;
> +			else
> +				*base = 8;
> +		} else
> +			*base = 10;
> +	}
> +	if (*base == 16 && s[0] == '0' && _tolower(s[1]) == 'x')
> +		s += 2;
> +	return s;
> +}
> +
> +/*
> + * Convert non-negative integer string representation in explicitly given radix
> + * to an integer.
> + * Return number of characters consumed maybe or-ed with overflow bit.
> + * If overflow occurs, result integer (incorrect) is still returned.
> + *
> + * Don't you dare use this function.
> + */
> +unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *p)

static

> +{
> +	unsigned long long res;
> +	unsigned int rv;
> +
> +	res = 0;
> +	rv = 0;
> +	while (1) {
> +		unsigned int c = *s;
> +		unsigned int lc = c | 0x20; /* don't tolower() this line */
> +		unsigned int val;
> +
> +		if ('0' <= c && c <= '9')
> +			val = c - '0';
> +		else if ('a' <= lc && lc <= 'f')
> +			val = lc - 'a' + 10;
> +		else
> +			break;
> +
> +		if (val >= base)
> +			break;
> +		/*
> +		 * Check for overflow only if we are within range of
> +		 * it in the max base we support (16)
> +		 */
> +		if (unlikely(res & (~0ull << 60))) {
> +			if (res > __div_u64(ULLONG_MAX - val, base))
> +				rv |= KSTRTOX_OVERFLOW;
> +		}
> +		res = res * base + val;
> +		rv++;
> +		s++;
> +	}
> +	*p = res;
> +	return rv;
> +}
 

-- 
Regards/Gruss,
    Boris.

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