arch/xtensa/lib/usercopy.S - arm/linux - Git at Google


            
            /*

            
             *  arch/xtensa/lib/usercopy.S

            
             *

            
             *  Copy to/from user space (derived from arch/xtensa/lib/hal/memcopy.S)

            
             *

            
             *  DO NOT COMBINE this function with <arch/xtensa/lib/hal/memcopy.S>.

            
             *  It needs to remain separate and distinct.  The hal files are part

            
             *  of the Xtensa link-time HAL, and those files may differ per

            
             *  processor configuration.  Patching the kernel for another

            
             *  processor configuration includes replacing the hal files, and we

            
             *  could lose the special functionality for accessing user-space

            
             *  memory during such a patch.  We sacrifice a little code space here

            
             *  in favor to simplify code maintenance.

            
             *

            
             *  This file is subject to the terms and conditions of the GNU General

            
             *  Public License.  See the file "COPYING" in the main directory of

            
             *  this archive for more details.

            
             *

            
             *  Copyright (C) 2002 Tensilica Inc.

            
             */


            /*

            
             * size_t __xtensa_copy_user (void *dst, const void *src, size_t len);

            
             *

            
             * The returned value is the number of bytes not copied.  Implies zero

            
             * is success.

            
             *

            
             * The general case algorithm is as follows:

            
             *   If the destination and source are both aligned,

            
             *     do 16B chunks with a loop, and then finish up with

            
             *     8B, 4B, 2B, and 1B copies conditional on the length.

            
             *   If destination is aligned and source unaligned,

            
             *     do the same, but use SRC to align the source data.

            
             *   If destination is unaligned, align it by conditionally

            
             *     copying 1B and 2B and then retest.

            
             *   This code tries to use fall-through braches for the common

            
             *     case of aligned destinations (except for the branches to

            
             *     the alignment label).

            
             *

            
             * Register use:

            
             *	a0/ return address

            
             *	a1/ stack pointer

            
             *	a2/ return value

            
             *	a3/ src

            
             *	a4/ length

            
             *	a5/ dst

            
             *	a6/ tmp

            
             *	a7/ tmp

            
             *	a8/ tmp

            
             *	a9/ tmp

            
             *	a10/ tmp

            
             *	a11/ original length

            
             */


            #include <variant/core.h>


            #ifdef __XTENSA_EB__

            
            #define ALIGN(R, W0, W1) src	R, W0, W1

            
            #define SSA8(R)	ssa8b R

            
            #else

            
            #define ALIGN(R, W0, W1) src	R, W1, W0

            
            #define SSA8(R)	ssa8l R

            
            #endif


            /* Load or store instructions that may cause exceptions use the EX macro. */


            #define EX(insn,reg1,reg2,offset,handler)	\

            
            9:	insn	reg1, reg2, offset;		\

            
            	.section __ex_table, "a";		\

            
            	.word	9b, handler;			\

            
            	.previous


            	.text

            
            	.align	4

            
            	.global	__xtensa_copy_user

            
            	.type	__xtensa_copy_user,@function

            
            __xtensa_copy_user:

            
            	entry	sp, 16		# minimal stack frame

            
            	# a2/ dst, a3/ src, a4/ len

            
            	mov	a5, a2		# copy dst so that a2 is return value

            
            	mov	a11, a4		# preserve original len for error case

            
            .Lcommon:

            
            	bbsi.l	a2, 0, .Ldst1mod2 # if dst is 1 mod 2

            
            	bbsi.l	a2, 1, .Ldst2mod4 # if dst is 2 mod 4

            
            .Ldstaligned:	# return here from .Ldstunaligned when dst is aligned

            
            	srli	a7, a4, 4	# number of loop iterations with 16B

            
            				# per iteration

            
            	movi	a8, 3		  # if source is also aligned,

            
            	bnone	a3, a8, .Laligned # then use word copy

            
            	SSA8(	a3)		# set shift amount from byte offset

            
            	bnez	a4, .Lsrcunaligned

            
            	movi	a2, 0		# return success for len==0

            
            	retw


            /*

            
             * Destination is unaligned

            
             */


            .Ldst1mod2:	# dst is only byte aligned

            
            	bltui	a4, 7, .Lbytecopy	# do short copies byte by byte


            	# copy 1 byte

            
            	EX(l8ui, a6, a3, 0, l_fixup)

            
            	addi	a3, a3,  1

            
            	EX(s8i, a6, a5,  0, s_fixup)

            
            	addi	a5, a5,  1

            
            	addi	a4, a4, -1

            
            	bbci.l	a5, 1, .Ldstaligned	# if dst is now aligned, then

            
            					# return to main algorithm

            
            .Ldst2mod4:	# dst 16-bit aligned

            
            	# copy 2 bytes

            
            	bltui	a4, 6, .Lbytecopy	# do short copies byte by byte

            
            	EX(l8ui, a6, a3, 0, l_fixup)

            
            	EX(l8ui, a7, a3, 1, l_fixup)

            
            	addi	a3, a3,  2

            
            	EX(s8i, a6, a5,  0, s_fixup)

            
            	EX(s8i, a7, a5,  1, s_fixup)

            
            	addi	a5, a5,  2

            
            	addi	a4, a4, -2

            
            	j	.Ldstaligned	# dst is now aligned, return to main algorithm


            /*

            
             * Byte by byte copy

            
             */

            
            	.align	4

            
            	.byte	0		# 1 mod 4 alignment for LOOPNEZ

            
            				# (0 mod 4 alignment for LBEG)

            
            .Lbytecopy:

            
            #if XCHAL_HAVE_LOOPS

            
            	loopnez	a4, .Lbytecopydone

            
            #else /* !XCHAL_HAVE_LOOPS */

            
            	beqz	a4, .Lbytecopydone

            
            	add	a7, a3, a4	# a7 = end address for source

            
            #endif /* !XCHAL_HAVE_LOOPS */

            
            .Lnextbyte:

            
            	EX(l8ui, a6, a3, 0, l_fixup)

            
            	addi	a3, a3, 1

            
            	EX(s8i, a6, a5, 0, s_fixup)

            
            	addi	a5, a5, 1

            
            #if !XCHAL_HAVE_LOOPS

            
            	blt	a3, a7, .Lnextbyte

            
            #endif /* !XCHAL_HAVE_LOOPS */

            
            .Lbytecopydone:

            
            	movi	a2, 0		# return success for len bytes copied

            
            	retw


            /*

            
             * Destination and source are word-aligned.

            
             */

            
            	# copy 16 bytes per iteration for word-aligned dst and word-aligned src

            
            	.align	4		# 1 mod 4 alignment for LOOPNEZ

            
            	.byte	0		# (0 mod 4 alignment for LBEG)

            
            .Laligned:

            
            #if XCHAL_HAVE_LOOPS

            
            	loopnez	a7, .Loop1done

            
            #else /* !XCHAL_HAVE_LOOPS */

            
            	beqz	a7, .Loop1done

            
            	slli	a8, a7, 4

            
            	add	a8, a8, a3	# a8 = end of last 16B source chunk

            
            #endif /* !XCHAL_HAVE_LOOPS */

            
            .Loop1:

            
            	EX(l32i, a6, a3,  0, l_fixup)

            
            	EX(l32i, a7, a3,  4, l_fixup)

            
            	EX(s32i, a6, a5,  0, s_fixup)

            
            	EX(l32i, a6, a3,  8, l_fixup)

            
            	EX(s32i, a7, a5,  4, s_fixup)

            
            	EX(l32i, a7, a3, 12, l_fixup)

            
            	EX(s32i, a6, a5,  8, s_fixup)

            
            	addi	a3, a3, 16

            
            	EX(s32i, a7, a5, 12, s_fixup)

            
            	addi	a5, a5, 16

            
            #if !XCHAL_HAVE_LOOPS

            
            	blt	a3, a8, .Loop1

            
            #endif /* !XCHAL_HAVE_LOOPS */

            
            .Loop1done:

            
            	bbci.l	a4, 3, .L2

            
            	# copy 8 bytes

            
            	EX(l32i, a6, a3,  0, l_fixup)

            
            	EX(l32i, a7, a3,  4, l_fixup)

            
            	addi	a3, a3,  8

            
            	EX(s32i, a6, a5,  0, s_fixup)

            
            	EX(s32i, a7, a5,  4, s_fixup)

            
            	addi	a5, a5,  8

            
            .L2:

            
            	bbci.l	a4, 2, .L3

            
            	# copy 4 bytes

            
            	EX(l32i, a6, a3,  0, l_fixup)

            
            	addi	a3, a3,  4

            
            	EX(s32i, a6, a5,  0, s_fixup)

            
            	addi	a5, a5,  4

            
            .L3:

            
            	bbci.l	a4, 1, .L4

            
            	# copy 2 bytes

            
            	EX(l16ui, a6, a3,  0, l_fixup)

            
            	addi	a3, a3,  2

            
            	EX(s16i,  a6, a5,  0, s_fixup)

            
            	addi	a5, a5,  2

            
            .L4:

            
            	bbci.l	a4, 0, .L5

            
            	# copy 1 byte

            
            	EX(l8ui, a6, a3,  0, l_fixup)

            
            	EX(s8i,  a6, a5,  0, s_fixup)

            
            .L5:

            
            	movi	a2, 0		# return success for len bytes copied

            
            	retw


            /*

            
             * Destination is aligned, Source is unaligned

            
             */


            	.align	4

            
            	.byte	0		# 1 mod 4 alignement for LOOPNEZ

            
            				# (0 mod 4 alignment for LBEG)

            
            .Lsrcunaligned:

            
            	# copy 16 bytes per iteration for word-aligned dst and unaligned src

            
            	and	a10, a3, a8	# save unalignment offset for below

            
            	sub	a3, a3, a10	# align a3 (to avoid sim warnings only; not needed for hardware)

            
            	EX(l32i, a6, a3, 0, l_fixup)	# load first word

            
            #if XCHAL_HAVE_LOOPS

            
            	loopnez	a7, .Loop2done

            
            #else /* !XCHAL_HAVE_LOOPS */

            
            	beqz	a7, .Loop2done

            
            	slli	a12, a7, 4

            
            	add	a12, a12, a3	# a12 = end of last 16B source chunk

            
            #endif /* !XCHAL_HAVE_LOOPS */

            
            .Loop2:

            
            	EX(l32i, a7, a3,  4, l_fixup)

            
            	EX(l32i, a8, a3,  8, l_fixup)

            
            	ALIGN(	a6, a6, a7)

            
            	EX(s32i, a6, a5,  0, s_fixup)

            
            	EX(l32i, a9, a3, 12, l_fixup)

            
            	ALIGN(	a7, a7, a8)

            
            	EX(s32i, a7, a5,  4, s_fixup)

            
            	EX(l32i, a6, a3, 16, l_fixup)

            
            	ALIGN(	a8, a8, a9)

            
            	EX(s32i, a8, a5,  8, s_fixup)

            
            	addi	a3, a3, 16

            
            	ALIGN(	a9, a9, a6)

            
            	EX(s32i, a9, a5, 12, s_fixup)

            
            	addi	a5, a5, 16

            
            #if !XCHAL_HAVE_LOOPS

            
            	blt	a3, a12, .Loop2

            
            #endif /* !XCHAL_HAVE_LOOPS */

            
            .Loop2done:

            
            	bbci.l	a4, 3, .L12

            
            	# copy 8 bytes

            
            	EX(l32i, a7, a3,  4, l_fixup)

            
            	EX(l32i, a8, a3,  8, l_fixup)

            
            	ALIGN(	a6, a6, a7)

            
            	EX(s32i, a6, a5,  0, s_fixup)

            
            	addi	a3, a3,  8

            
            	ALIGN(	a7, a7, a8)

            
            	EX(s32i, a7, a5,  4, s_fixup)

            
            	addi	a5, a5,  8

            
            	mov	a6, a8

            
            .L12:

            
            	bbci.l	a4, 2, .L13

            
            	# copy 4 bytes

            
            	EX(l32i, a7, a3,  4, l_fixup)

            
            	addi	a3, a3,  4

            
            	ALIGN(	a6, a6, a7)

            
            	EX(s32i, a6, a5,  0, s_fixup)

            
            	addi	a5, a5,  4

            
            	mov	a6, a7

            
            .L13:

            
            	add	a3, a3, a10	# readjust a3 with correct misalignment

            
            	bbci.l	a4, 1, .L14

            
            	# copy 2 bytes

            
            	EX(l8ui, a6, a3,  0, l_fixup)

            
            	EX(l8ui, a7, a3,  1, l_fixup)

            
            	addi	a3, a3,  2

            
            	EX(s8i, a6, a5,  0, s_fixup)

            
            	EX(s8i, a7, a5,  1, s_fixup)

            
            	addi	a5, a5,  2

            
            .L14:

            
            	bbci.l	a4, 0, .L15

            
            	# copy 1 byte

            
            	EX(l8ui, a6, a3,  0, l_fixup)

            
            	EX(s8i,  a6, a5,  0, s_fixup)

            
            .L15:

            
            	movi	a2, 0		# return success for len bytes copied

            
            	retw


            	.section .fixup, "ax"

            
            	.align	4


            /* a2 = original dst; a5 = current dst; a11= original len

            
             * bytes_copied = a5 - a2

            
             * retval = bytes_not_copied = original len - bytes_copied

            
             * retval = a11 - (a5 - a2)

            
             *

            
             * Clearing the remaining pieces of kernel memory plugs security

            
             * holes.  This functionality is the equivalent of the *_zeroing

            
             * functions that some architectures provide.

            
             */


            .Lmemset:

            
            	.word	memset


            s_fixup:

            
            	sub	a2, a5, a2	/* a2 <-- bytes copied */

            
            	sub	a2, a11, a2	/* a2 <-- bytes not copied */

            
            	retw


            l_fixup:

            
            	sub	a2, a5, a2	/* a2 <-- bytes copied */

            
            	sub	a2, a11, a2	/* a2 <-- bytes not copied == return value */


            	/* void *memset(void *s, int c, size_t n); */

            
            	mov	a6, a5		/* s */

            
            	movi	a7, 0		/* c */

            
            	mov	a8, a2		/* n */

            
            	l32r	a4, .Lmemset

            
            	callx4	a4

            
            	/* Ignore memset return value in a6. */

            
            	/* a2 still contains bytes not copied. */

            
            	retw
	/*
	* arch/xtensa/lib/usercopy.S
	*
	* Copy to/from user space (derived from arch/xtensa/lib/hal/memcopy.S)
	*
	* DO NOT COMBINE this function with <arch/xtensa/lib/hal/memcopy.S>.
	* It needs to remain separate and distinct. The hal files are part
	* of the Xtensa link-time HAL, and those files may differ per
	* processor configuration. Patching the kernel for another
	* processor configuration includes replacing the hal files, and we
	* could lose the special functionality for accessing user-space
	* memory during such a patch. We sacrifice a little code space here
	* in favor to simplify code maintenance.
	*
	* This file is subject to the terms and conditions of the GNU General
	* Public License. See the file "COPYING" in the main directory of
	* this archive for more details.
	*
	* Copyright (C) 2002 Tensilica Inc.
	*/


	/*
	* size_t __xtensa_copy_user (void dst, const void src, size_t len);
	*
	* The returned value is the number of bytes not copied. Implies zero
	* is success.
	*
	* The general case algorithm is as follows:
	* If the destination and source are both aligned,
	* do 16B chunks with a loop, and then finish up with
	* 8B, 4B, 2B, and 1B copies conditional on the length.
	* If destination is aligned and source unaligned,
	* do the same, but use SRC to align the source data.
	* If destination is unaligned, align it by conditionally
	* copying 1B and 2B and then retest.
	* This code tries to use fall-through braches for the common
	* case of aligned destinations (except for the branches to
	* the alignment label).
	*
	* Register use:
	* a0/ return address
	* a1/ stack pointer
	* a2/ return value
	* a3/ src
	* a4/ length
	* a5/ dst
	* a6/ tmp
	* a7/ tmp
	* a8/ tmp
	* a9/ tmp
	* a10/ tmp
	* a11/ original length
	*/

	#include <variant/core.h>

	#ifdef __XTENSA_EB__
	#define ALIGN(R, W0, W1) src R, W0, W1
	#define SSA8(R) ssa8b R
	#else
	#define ALIGN(R, W0, W1) src R, W1, W0
	#define SSA8(R) ssa8l R
	#endif

	/* Load or store instructions that may cause exceptions use the EX macro. */

	#define EX(insn,reg1,reg2,offset,handler) \
	9: insn reg1, reg2, offset; \
	.section __ex_table, "a"; \
	.word 9b, handler; \
	.previous


	.text
	.align 4
	.global __xtensa_copy_user
	.type __xtensa_copy_user,@function
	__xtensa_copy_user:
	entry sp, 16 # minimal stack frame
	# a2/ dst, a3/ src, a4/ len
	mov a5, a2 # copy dst so that a2 is return value
	mov a11, a4 # preserve original len for error case
	.Lcommon:
	bbsi.l a2, 0, .Ldst1mod2 # if dst is 1 mod 2
	bbsi.l a2, 1, .Ldst2mod4 # if dst is 2 mod 4
	.Ldstaligned: # return here from .Ldstunaligned when dst is aligned
	srli a7, a4, 4 # number of loop iterations with 16B
	# per iteration
	movi a8, 3 # if source is also aligned,
	bnone a3, a8, .Laligned # then use word copy
	SSA8( a3) # set shift amount from byte offset
	bnez a4, .Lsrcunaligned
	movi a2, 0 # return success for len==0
	retw

	/*
	* Destination is unaligned
	*/

	.Ldst1mod2: # dst is only byte aligned
	bltui a4, 7, .Lbytecopy # do short copies byte by byte

	# copy 1 byte
	EX(l8ui, a6, a3, 0, l_fixup)
	addi a3, a3, 1
	EX(s8i, a6, a5, 0, s_fixup)
	addi a5, a5, 1
	addi a4, a4, -1
	bbci.l a5, 1, .Ldstaligned # if dst is now aligned, then
	# return to main algorithm
	.Ldst2mod4: # dst 16-bit aligned
	# copy 2 bytes
	bltui a4, 6, .Lbytecopy # do short copies byte by byte
	EX(l8ui, a6, a3, 0, l_fixup)
	EX(l8ui, a7, a3, 1, l_fixup)
	addi a3, a3, 2
	EX(s8i, a6, a5, 0, s_fixup)
	EX(s8i, a7, a5, 1, s_fixup)
	addi a5, a5, 2
	addi a4, a4, -2
	j .Ldstaligned # dst is now aligned, return to main algorithm

	/*
	* Byte by byte copy
	*/
	.align 4
	.byte 0 # 1 mod 4 alignment for LOOPNEZ
	# (0 mod 4 alignment for LBEG)
	.Lbytecopy:
	#if XCHAL_HAVE_LOOPS
	loopnez a4, .Lbytecopydone
	#else /* !XCHAL_HAVE_LOOPS */
	beqz a4, .Lbytecopydone
	add a7, a3, a4 # a7 = end address for source
	#endif /* !XCHAL_HAVE_LOOPS */
	.Lnextbyte:
	EX(l8ui, a6, a3, 0, l_fixup)
	addi a3, a3, 1
	EX(s8i, a6, a5, 0, s_fixup)
	addi a5, a5, 1
	#if !XCHAL_HAVE_LOOPS
	blt a3, a7, .Lnextbyte
	#endif /* !XCHAL_HAVE_LOOPS */
	.Lbytecopydone:
	movi a2, 0 # return success for len bytes copied
	retw

	/*
	* Destination and source are word-aligned.
	*/
	# copy 16 bytes per iteration for word-aligned dst and word-aligned src
	.align 4 # 1 mod 4 alignment for LOOPNEZ
	.byte 0 # (0 mod 4 alignment for LBEG)
	.Laligned:
	#if XCHAL_HAVE_LOOPS
	loopnez a7, .Loop1done
	#else /* !XCHAL_HAVE_LOOPS */
	beqz a7, .Loop1done
	slli a8, a7, 4
	add a8, a8, a3 # a8 = end of last 16B source chunk
	#endif /* !XCHAL_HAVE_LOOPS */
	.Loop1:
	EX(l32i, a6, a3, 0, l_fixup)
	EX(l32i, a7, a3, 4, l_fixup)
	EX(s32i, a6, a5, 0, s_fixup)
	EX(l32i, a6, a3, 8, l_fixup)
	EX(s32i, a7, a5, 4, s_fixup)
	EX(l32i, a7, a3, 12, l_fixup)
	EX(s32i, a6, a5, 8, s_fixup)
	addi a3, a3, 16
	EX(s32i, a7, a5, 12, s_fixup)
	addi a5, a5, 16
	#if !XCHAL_HAVE_LOOPS
	blt a3, a8, .Loop1
	#endif /* !XCHAL_HAVE_LOOPS */
	.Loop1done:
	bbci.l a4, 3, .L2
	# copy 8 bytes
	EX(l32i, a6, a3, 0, l_fixup)
	EX(l32i, a7, a3, 4, l_fixup)
	addi a3, a3, 8
	EX(s32i, a6, a5, 0, s_fixup)
	EX(s32i, a7, a5, 4, s_fixup)
	addi a5, a5, 8
	.L2:
	bbci.l a4, 2, .L3
	# copy 4 bytes
	EX(l32i, a6, a3, 0, l_fixup)
	addi a3, a3, 4
	EX(s32i, a6, a5, 0, s_fixup)
	addi a5, a5, 4
	.L3:
	bbci.l a4, 1, .L4
	# copy 2 bytes
	EX(l16ui, a6, a3, 0, l_fixup)
	addi a3, a3, 2
	EX(s16i, a6, a5, 0, s_fixup)
	addi a5, a5, 2
	.L4:
	bbci.l a4, 0, .L5
	# copy 1 byte
	EX(l8ui, a6, a3, 0, l_fixup)
	EX(s8i, a6, a5, 0, s_fixup)
	.L5:
	movi a2, 0 # return success for len bytes copied
	retw

	/*
	* Destination is aligned, Source is unaligned
	*/

	.align 4
	.byte 0 # 1 mod 4 alignement for LOOPNEZ
	# (0 mod 4 alignment for LBEG)
	.Lsrcunaligned:
	# copy 16 bytes per iteration for word-aligned dst and unaligned src
	and a10, a3, a8 # save unalignment offset for below
	sub a3, a3, a10 # align a3 (to avoid sim warnings only; not needed for hardware)
	EX(l32i, a6, a3, 0, l_fixup) # load first word
	#if XCHAL_HAVE_LOOPS
	loopnez a7, .Loop2done
	#else /* !XCHAL_HAVE_LOOPS */
	beqz a7, .Loop2done
	slli a12, a7, 4
	add a12, a12, a3 # a12 = end of last 16B source chunk
	#endif /* !XCHAL_HAVE_LOOPS */
	.Loop2:
	EX(l32i, a7, a3, 4, l_fixup)
	EX(l32i, a8, a3, 8, l_fixup)
	ALIGN( a6, a6, a7)
	EX(s32i, a6, a5, 0, s_fixup)
	EX(l32i, a9, a3, 12, l_fixup)
	ALIGN( a7, a7, a8)
	EX(s32i, a7, a5, 4, s_fixup)
	EX(l32i, a6, a3, 16, l_fixup)
	ALIGN( a8, a8, a9)
	EX(s32i, a8, a5, 8, s_fixup)
	addi a3, a3, 16
	ALIGN( a9, a9, a6)
	EX(s32i, a9, a5, 12, s_fixup)
	addi a5, a5, 16
	#if !XCHAL_HAVE_LOOPS
	blt a3, a12, .Loop2
	#endif /* !XCHAL_HAVE_LOOPS */
	.Loop2done:
	bbci.l a4, 3, .L12
	# copy 8 bytes
	EX(l32i, a7, a3, 4, l_fixup)
	EX(l32i, a8, a3, 8, l_fixup)
	ALIGN( a6, a6, a7)
	EX(s32i, a6, a5, 0, s_fixup)
	addi a3, a3, 8
	ALIGN( a7, a7, a8)
	EX(s32i, a7, a5, 4, s_fixup)
	addi a5, a5, 8
	mov a6, a8
	.L12:
	bbci.l a4, 2, .L13
	# copy 4 bytes
	EX(l32i, a7, a3, 4, l_fixup)
	addi a3, a3, 4
	ALIGN( a6, a6, a7)
	EX(s32i, a6, a5, 0, s_fixup)
	addi a5, a5, 4
	mov a6, a7
	.L13:
	add a3, a3, a10 # readjust a3 with correct misalignment
	bbci.l a4, 1, .L14
	# copy 2 bytes
	EX(l8ui, a6, a3, 0, l_fixup)
	EX(l8ui, a7, a3, 1, l_fixup)
	addi a3, a3, 2
	EX(s8i, a6, a5, 0, s_fixup)
	EX(s8i, a7, a5, 1, s_fixup)
	addi a5, a5, 2
	.L14:
	bbci.l a4, 0, .L15
	# copy 1 byte
	EX(l8ui, a6, a3, 0, l_fixup)
	EX(s8i, a6, a5, 0, s_fixup)
	.L15:
	movi a2, 0 # return success for len bytes copied
	retw


	.section .fixup, "ax"
	.align 4

	/* a2 = original dst; a5 = current dst; a11= original len
	* bytes_copied = a5 - a2
	* retval = bytes_not_copied = original len - bytes_copied
	* retval = a11 - (a5 - a2)
	*
	* Clearing the remaining pieces of kernel memory plugs security
	* holes. This functionality is the equivalent of the *_zeroing
	* functions that some architectures provide.
	*/

	.Lmemset:
	.word memset

	s_fixup:
	sub a2, a5, a2 /* a2 <-- bytes copied */
	sub a2, a11, a2 /* a2 <-- bytes not copied */
	retw

	l_fixup:
	sub a2, a5, a2 /* a2 <-- bytes copied */
	sub a2, a11, a2 /* a2 <-- bytes not copied == return value */

	/* void memset(void s, int c, size_t n); */
	mov a6, a5 /* s */
	movi a7, 0 /* c */
	mov a8, a2 /* n */
	l32r a4, .Lmemset
	callx4 a4
	/* Ignore memset return value in a6. */
	/* a2 still contains bytes not copied. */
	retw