root/arch/arm64/lib/clear_user.S

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Based on arch/arm/lib/clear_user.S
   4  *
   5  * Copyright (C) 2012 ARM Ltd.
   6  */
   7 #include <linux/linkage.h>
   8 
   9 #include <asm/asm-uaccess.h>
  10 #include <asm/assembler.h>
  11 
  12         .text
  13 
  14 /* Prototype: int __arch_clear_user(void *addr, size_t sz)
  15  * Purpose  : clear some user memory
  16  * Params   : addr - user memory address to clear
  17  *          : sz   - number of bytes to clear
  18  * Returns  : number of bytes NOT cleared
  19  *
  20  * Alignment fixed up by hardware.
  21  */
  22 ENTRY(__arch_clear_user)
  23         mov     x2, x1                  // save the size for fixup return
  24         subs    x1, x1, #8
  25         b.mi    2f
  26 1:
  27 uao_user_alternative 9f, str, sttr, xzr, x0, 8
  28         subs    x1, x1, #8
  29         b.pl    1b
  30 2:      adds    x1, x1, #4
  31         b.mi    3f
  32 uao_user_alternative 9f, str, sttr, wzr, x0, 4
  33         sub     x1, x1, #4
  34 3:      adds    x1, x1, #2
  35         b.mi    4f
  36 uao_user_alternative 9f, strh, sttrh, wzr, x0, 2
  37         sub     x1, x1, #2
  38 4:      adds    x1, x1, #1
  39         b.mi    5f
  40 uao_user_alternative 9f, strb, sttrb, wzr, x0, 0
  41 5:      mov     x0, #0
  42         ret
  43 ENDPROC(__arch_clear_user)
  44 EXPORT_SYMBOL(__arch_clear_user)
  45 
  46         .section .fixup,"ax"
  47         .align  2
  48 9:      mov     x0, x2                  // return the original size
  49         ret
  50         .previous