Re: [Xen-devel] [PATCH RFC 05/25] Introduce clear_user

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.12.11 at 19:19, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> --- a/xen/arch/x86/usercopy.c
> +++ b/xen/arch/x86/usercopy.c
> @@ -110,6 +110,42 @@ copy_to_user(void __user *to, const void *from, unsigned 
> n)
>      return n;
>  }
>  
> +#define __do_clear_user(addr,size)                                   \
> +do {                                                                 \
> +     int __d0;                                                       \

This should be 'long' to be forward compatible (current gcc likely doesn't
care), and to cope with eventual future compat mode users passing in a
32-bit 'addr'.

> +     __asm__ __volatile__(                                           \
> +             "0:     rep; stosl\n"                                   \
> +             "       movl %2,%0\n"                                   \
> +             "1:     rep; stosb\n"                                   \
> +             "2:\n"                                                  \
> +             ".section .fixup,\"ax\"\n"                              \
> +             "3:     lea 0(%2,%0,4),%0\n"                            \
> +             "       jmp 2b\n"                                       \
> +             ".previous\n"                                           \
> +             _ASM_EXTABLE(0b,3b)                                     \
> +             _ASM_EXTABLE(1b,2b)                                     \
> +             : "=&c"(size), "=&D" (__d0)                             \
> +             : "r"(size & 3), "0"(size / 4), "1"(addr), "a"(0));     \

For that latter case at least, casting 'addr' to long may also be necessary.

Jan

> +} while (0)



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