Hi All,
Here is the code for __do_clear_user, I am not getting how does it work. Can
any one please explain?
#define __do_clear_user(addr,size) \
do { \
int __d0; \
might_sleep(); \
__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)); \
} while (0)
/**
* clear_user: - Zero a block of memory in user space.
* @to: Destination address, in user space.
* @n: Number of bytes to zero.
*
* Zero a block of memory in user space.
*
* Returns number of bytes that could not be cleared.
* On success, this will be zero.
*/
unsigned long
clear_user(void __user *to, unsigned long n)
{
might_sleep();
if (access_ok(VERIFY_WRITE, to, n))
__do_clear_user(to, n);
return n;
}
EXPORT_SYMBOL(clear_user);
clear_user() is the function which is calling __do_clear_user(), from the
context I can understand it is clearing the user space buffer. But how does
it work?
Thanks and Regards,
Prasad.
