Subject: [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm

From: [email-masked] (Arnd Bergmann)
Date: Tue, 29 Mar 2016 12:19:49 +0200

On Monday 28 March 2016 12:19:03 Chen Gang wrote:
> __xl(R0 in little endian system, or R1 in big endian system) is corrupted
> after calling __do_div64 and compiler is not informed about this in
> macro __do_div_asm. If n is used again afterwards, __xl won't be
> reloaded and n will contain incorrect value.
> 
> Signed-off-by: Chen Gang <[email-masked]>
> Signed-off-by: Chen Gang <[email-masked]>
> ---

How did you find this? Did you run into this problem on a live system
or see it through inspection?

>  arch/arm/include/asm/div64.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
> index e1f0776..1a6e91a 100644
> --- a/arch/arm/include/asm/div64.h
> +++ b/arch/arm/include/asm/div64.h
> @@ -35,12 +35,14 @@ static inline uint32_t __div64_32(uint64_t *n, uint32_t base)
>         register unsigned long long __n   asm("r0") = *n;
>         register unsigned long long __res asm("r2");
>         register unsigned int __rem       asm(__xh);
> +       register unsigned int __clobber   asm(__xl);
>         asm(    __asmeq("%0", __xh)
>                 __asmeq("%1", "r2")
> +               __asmeq("%3", "r0")
> +               __asmeq("%4", "r4")
>                 __asmeq("%2", "r0")
> -               __asmeq("%3", "r4")
>                 "bl     __do_div64"
> -               : "=r" (__rem), "=r" (__res)
> +               : "=r" (__rem), "=r" (__res), "=r" (__clobber)
>                 : "r" (__n), "r" (__base)
>                 : "ip", "lr", "cc");
>         *n = __res;

Doesn't the clobber normally go in the third line along with
"ip" and "lr"?

	Arnd