On 2012-05-09 15:19, Dan Carpenter wrote:
On Wed, May 09, 2012 at 12:01:25PM +0100, Ian Abbott wrote:
Are there any handy macros for casting pointers to __user pointers,
something like
#define _user(p) ((typeof(*(p)) __user *)(p))
but preferably without the repeated expansion of 'p' in case of
side-effects?
typeof() doesn't have side effects.
#include<stdio.h>
int main(void)
{
int x = 0;
typeof(x++) y;
printf("%d\n", x);
return 0;
}
regards,
dan carpenter
Yes, you're correct of course. I was unnecessarily worried about the
double-expansion of the macro parameter but it's safe in this case.
BTW, the intention of this macro is so you can write things like:
copy_from_user(data, _user(insn.data), insn.n * sizeof(insn.data[0]));
instead of:
copy_from_user(data, (unsigned int __user *)insn.data, insn.n *
sizeof(insn.data[0]));
where the member insn.data is a 'unsigned int *' but is used for both
__user pointers and kernel pointers.
--
-=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@xxxxxxxxx> )=-
-=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-
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