linux/arch/x86/lib/getuser_64.S

/*
 * __get_user functions.
 *
 * (C) Copyright 1998 Linus Torvalds
 * (C) Copyright 2005 Andi Kleen
 *
 * These functions have a non-standard call interface
 * to make them more efficient, especially as they
 * return an error value in addition to the "real"
 * return value.
 */

/*
 * __get_user_X
 *
 * Inputs:	%rcx contains the address.
 *		The register is modified, but all changes are undone
 *		before returning because the C code doesn't know about it.
 *
 * Outputs:	%rax is error code (0 or -EFAULT)
 *		%rdx contains zero-extended value
 * 
 * %r8 is destroyed.
 *
 * These functions should not modify any other registers,
 * as they get called from within inline assembly.
 */

#include <linux/linkage.h>
#include <asm/dwarf2.h>
#include <asm/page.h>
#include <asm/errno.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>

	.text
ENTRY(__get_user_1)
	CFI_STARTPROC
	GET_THREAD_INFO(%rdx)
	cmp TI_addr_limit(%rdx),%rax
	jae bad_get_user
1:	movzb (%rax),%edx
	xor %eax,%eax
	ret
	CFI_ENDPROC
ENDPROC(__get_user_1)

ENTRY(__get_user_2)
	CFI_STARTPROC
	add $1,%rax
	jc bad_get_user
	GET_THREAD_INFO(%rdx)
	cmp TI_addr_limit(%rdx),%rax
	jae bad_get_user
2:	movzwl -1(%rax),%edx
	xor %eax,%eax
	ret
	CFI_ENDPROC
ENDPROC(__get_user_2)

ENTRY(__get_user_4)
	CFI_STARTPROC
	add $3,%rax
	jc bad_get_user
	GET_THREAD_INFO(%rdx)
	cmp TI_addr_limit(%rdx),%rax
	jae bad_get_user
3:	mov -3(%rax),%edx
	xor %eax,%eax
	ret
	CFI_ENDPROC
ENDPROC(__get_user_4)

ENTRY(__get_user_8)
	CFI_STARTPROC
	add $7,%rax
	jc bad_get_user
	GET_THREAD_INFO(%rdx)
	cmp TI_addr_limit(%rdx),%rax
	jae	bad_get_user
4:	movq -7(%rax),%rdx
	xor %eax,%eax
	ret
	CFI_ENDPROC
ENDPROC(__get_user_8)

bad_get_user:
	CFI_STARTPROC
	xor %edx,%edx
	mov $(-EFAULT),%rax
	ret
	CFI_ENDPROC
END(bad_get_user)

.section __ex_table,"a"
	.quad 1b,bad_get_user
	.quad 2b,bad_get_user
	.quad 3b,bad_get_user
	.quad 4b,bad_get_user
.previous