root/arch/x86/lib/getuser.S

/*
 * __get_user functions.
 *
 * (C) Copyright 1998 Linus Torvalds
 * (C) Copyright 2005 Andi Kleen
 * (C) Copyright 2008 Glauber Costa
 *
 * 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:      %[r|e]ax contains the address.
 *              The register is modified, but all changes are undone
 *              before returning because the C code doesn't know about it.
 *
 * Outputs:     %[r|e]ax is error code (0 or -EFAULT)
 *              %[r|e]dx contains zero-extended value
 *
 *
 * 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>
#include <asm/asm.h>

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

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

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

#ifdef CONFIG_X86_64
ENTRY(__get_user_8)
        CFI_STARTPROC
        add $7,%_ASM_AX
        jc bad_get_user
        GET_THREAD_INFO(%_ASM_DX)
        cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
        jae     bad_get_user
4:      movq -7(%_ASM_AX),%_ASM_DX
        xor %eax,%eax
        ret
        CFI_ENDPROC
ENDPROC(__get_user_8)
#endif

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

.section __ex_table,"a"
        _ASM_PTR 1b,bad_get_user
        _ASM_PTR 2b,bad_get_user
        _ASM_PTR 3b,bad_get_user
#ifdef CONFIG_X86_64
        _ASM_PTR 4b,bad_get_user
#endif