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linux/arch/arm26/lib/uaccess-user.S
Linus Torvalds 1da177e4c3 Linux-2.6.12-rc2 
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00

719 lines
18 KiB
ArmAsm
Raw Blame History

/*
* linux/arch/arm26/lib/uaccess-user.S
*
* Copyright (C) 1995, 1996,1997,1998 Russell King
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* Routines to block copy data to/from user memory
* These are highly optimised both for the 4k page size
* and for various alignments.
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/errno.h>
#include <asm/page.h>
.text
//FIXME - surely this can be done in C not asm, removing the problem of keeping C and asm in sync? (this is a struct uaccess_t)
.globl uaccess_user
uaccess_user:
.word uaccess_user_put_byte
.word uaccess_user_get_byte
.word uaccess_user_put_half
.word uaccess_user_get_half
.word uaccess_user_put_word
.word uaccess_user_get_word
.word uaccess_user_put_dword
.word uaccess_user_copy_from_user
.word uaccess_user_copy_to_user
.word uaccess_user_clear_user
.word uaccess_user_strncpy_from_user
.word uaccess_user_strnlen_user
@ In : r0 = x, r1 = addr, r2 = error
@ Out: r2 = error
uaccess_user_put_byte:
stmfd sp!, {lr}
USER( strbt r0, [r1])
ldmfd sp!, {pc}^
@ In : r0 = x, r1 = addr, r2 = error
@ Out: r2 = error
uaccess_user_put_half:
stmfd sp!, {lr}
USER( strbt r0, [r1], #1)
mov r0, r0, lsr #8
USER( strbt r0, [r1])
ldmfd sp!, {pc}^
@ In : r0 = x, r1 = addr, r2 = error
@ Out: r2 = error
uaccess_user_put_word:
stmfd sp!, {lr}
USER( strt r0, [r1])
ldmfd sp!, {pc}^
@ In : r0 = x, r1 = addr, r2 = error
@ Out: r2 = error
uaccess_user_put_dword:
stmfd sp!, {lr}
USER( strt r0, [r1], #4)
USER( strt r0, [r1], #0)
ldmfd sp!, {pc}^
9001: mov r2, #-EFAULT
ldmfd sp!, {pc}^
@ In : r0 = addr, r1 = error
@ Out: r0 = x, r1 = error
uaccess_user_get_byte:
stmfd sp!, {lr}
USER( ldrbt r0, [r0])
ldmfd sp!, {pc}^
@ In : r0 = addr, r1 = error
@ Out: r0 = x, r1 = error
uaccess_user_get_half:
stmfd sp!, {lr}
USER( ldrt r0, [r0])
mov r0, r0, lsl #16
mov r0, r0, lsr #16
ldmfd sp!, {pc}^
@ In : r0 = addr, r1 = error
@ Out: r0 = x, r1 = error
uaccess_user_get_word:
stmfd sp!, {lr}
USER( ldrt r0, [r0])
ldmfd sp!, {pc}^
9001: mov r1, #-EFAULT
ldmfd sp!, {pc}^
/* Prototype: int uaccess_user_copy_to_user(void *to, const char *from, size_t n)
* Purpose : copy a block to user memory from kernel memory
* Params : to - user memory
* : from - kernel memory
* : n - number of bytes to copy
* Returns : Number of bytes NOT copied.
*/
.c2u_dest_not_aligned:
rsb ip, ip, #4
cmp ip, #2
ldrb r3, [r1], #1
USER( strbt r3, [r0], #1) @ May fault
ldrgeb r3, [r1], #1
USER( strgebt r3, [r0], #1) @ May fault
ldrgtb r3, [r1], #1
USER( strgtbt r3, [r0], #1) @ May fault
sub r2, r2, ip
b .c2u_dest_aligned
ENTRY(uaccess_user_copy_to_user)
stmfd sp!, {r2, r4 - r7, lr}
cmp r2, #4
blt .c2u_not_enough
ands ip, r0, #3
bne .c2u_dest_not_aligned
.c2u_dest_aligned:
ands ip, r1, #3
bne .c2u_src_not_aligned
/*
* Seeing as there has to be at least 8 bytes to copy, we can
* copy one word, and force a user-mode page fault...
*/
.c2u_0fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .c2u_0nowords
ldr r3, [r1], #4
USER( strt r3, [r0], #4) @ May fault
mov ip, r0, lsl #32 - PAGE_SHIFT @ On each page, use a ld/st??t instruction
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .c2u_0fupi
/*
* ip = max no. of bytes to copy before needing another "strt" insn
*/
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #32
blt .c2u_0rem8lp
.c2u_0cpy8lp: ldmia r1!, {r3 - r6}
stmia r0!, {r3 - r6} @ Shouldnt fault
ldmia r1!, {r3 - r6}
stmia r0!, {r3 - r6} @ Shouldnt fault
subs ip, ip, #32
bpl .c2u_0cpy8lp
.c2u_0rem8lp: cmn ip, #16
ldmgeia r1!, {r3 - r6}
stmgeia r0!, {r3 - r6} @ Shouldnt fault
tst ip, #8
ldmneia r1!, {r3 - r4}
stmneia r0!, {r3 - r4} @ Shouldnt fault
tst ip, #4
ldrne r3, [r1], #4
strnet r3, [r0], #4 @ Shouldnt fault
ands ip, ip, #3
beq .c2u_0fupi
.c2u_0nowords: teq ip, #0
beq .c2u_finished
.c2u_nowords: cmp ip, #2
ldrb r3, [r1], #1
USER( strbt r3, [r0], #1) @ May fault
ldrgeb r3, [r1], #1
USER( strgebt r3, [r0], #1) @ May fault
ldrgtb r3, [r1], #1
USER( strgtbt r3, [r0], #1) @ May fault
b .c2u_finished
.c2u_not_enough:
movs ip, r2
bne .c2u_nowords
.c2u_finished: mov r0, #0
LOADREGS(fd,sp!,{r2, r4 - r7, pc})
.c2u_src_not_aligned:
bic r1, r1, #3
ldr r7, [r1], #4
cmp ip, #2
bgt .c2u_3fupi
beq .c2u_2fupi
.c2u_1fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .c2u_1nowords
mov r3, r7, pull #8
ldr r7, [r1], #4
orr r3, r3, r7, push #24
USER( strt r3, [r0], #4) @ May fault
mov ip, r0, lsl #32 - PAGE_SHIFT
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .c2u_1fupi
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #16
blt .c2u_1rem8lp
.c2u_1cpy8lp: mov r3, r7, pull #8
ldmia r1!, {r4 - r7}
orr r3, r3, r4, push #24
mov r4, r4, pull #8
orr r4, r4, r5, push #24
mov r5, r5, pull #8
orr r5, r5, r6, push #24
mov r6, r6, pull #8
orr r6, r6, r7, push #24
stmia r0!, {r3 - r6} @ Shouldnt fault
subs ip, ip, #16
bpl .c2u_1cpy8lp
.c2u_1rem8lp: tst ip, #8
movne r3, r7, pull #8
ldmneia r1!, {r4, r7}
orrne r3, r3, r4, push #24
movne r4, r4, pull #8
orrne r4, r4, r7, push #24
stmneia r0!, {r3 - r4} @ Shouldnt fault
tst ip, #4
movne r3, r7, pull #8
ldrne r7, [r1], #4
orrne r3, r3, r7, push #24
strnet r3, [r0], #4 @ Shouldnt fault
ands ip, ip, #3
beq .c2u_1fupi
.c2u_1nowords: mov r3, r7, lsr #byte(1)
teq ip, #0
beq .c2u_finished
cmp ip, #2
USER( strbt r3, [r0], #1) @ May fault
movge r3, r7, lsr #byte(2)
USER( strgebt r3, [r0], #1) @ May fault
movgt r3, r7, lsr #byte(3)
USER( strgtbt r3, [r0], #1) @ May fault
b .c2u_finished
.c2u_2fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .c2u_2nowords
mov r3, r7, pull #16
ldr r7, [r1], #4
orr r3, r3, r7, push #16
USER( strt r3, [r0], #4) @ May fault
mov ip, r0, lsl #32 - PAGE_SHIFT
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .c2u_2fupi
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #16
blt .c2u_2rem8lp
.c2u_2cpy8lp: mov r3, r7, pull #16
ldmia r1!, {r4 - r7}
orr r3, r3, r4, push #16
mov r4, r4, pull #16
orr r4, r4, r5, push #16
mov r5, r5, pull #16
orr r5, r5, r6, push #16
mov r6, r6, pull #16
orr r6, r6, r7, push #16
stmia r0!, {r3 - r6} @ Shouldnt fault
subs ip, ip, #16
bpl .c2u_2cpy8lp
.c2u_2rem8lp: tst ip, #8
movne r3, r7, pull #16
ldmneia r1!, {r4, r7}
orrne r3, r3, r4, push #16
movne r4, r4, pull #16
orrne r4, r4, r7, push #16
stmneia r0!, {r3 - r4} @ Shouldnt fault
tst ip, #4
movne r3, r7, pull #16
ldrne r7, [r1], #4
orrne r3, r3, r7, push #16
strnet r3, [r0], #4 @ Shouldnt fault
ands ip, ip, #3
beq .c2u_2fupi
.c2u_2nowords: mov r3, r7, lsr #byte(2)
teq ip, #0
beq .c2u_finished
cmp ip, #2
USER( strbt r3, [r0], #1) @ May fault
movge r3, r7, lsr #byte(3)
USER( strgebt r3, [r0], #1) @ May fault
ldrgtb r3, [r1], #0
USER( strgtbt r3, [r0], #1) @ May fault
b .c2u_finished
.c2u_3fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .c2u_3nowords
mov r3, r7, pull #24
ldr r7, [r1], #4
orr r3, r3, r7, push #8
USER( strt r3, [r0], #4) @ May fault
mov ip, r0, lsl #32 - PAGE_SHIFT
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .c2u_3fupi
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #16
blt .c2u_3rem8lp
.c2u_3cpy8lp: mov r3, r7, pull #24
ldmia r1!, {r4 - r7}
orr r3, r3, r4, push #8
mov r4, r4, pull #24
orr r4, r4, r5, push #8
mov r5, r5, pull #24
orr r5, r5, r6, push #8
mov r6, r6, pull #24
orr r6, r6, r7, push #8
stmia r0!, {r3 - r6} @ Shouldnt fault
subs ip, ip, #16
bpl .c2u_3cpy8lp
.c2u_3rem8lp: tst ip, #8
movne r3, r7, pull #24
ldmneia r1!, {r4, r7}
orrne r3, r3, r4, push #8
movne r4, r4, pull #24
orrne r4, r4, r7, push #8
stmneia r0!, {r3 - r4} @ Shouldnt fault
tst ip, #4
movne r3, r7, pull #24
ldrne r7, [r1], #4
orrne r3, r3, r7, push #8
strnet r3, [r0], #4 @ Shouldnt fault
ands ip, ip, #3
beq .c2u_3fupi
.c2u_3nowords: mov r3, r7, lsr #byte(3)
teq ip, #0
beq .c2u_finished
cmp ip, #2
USER( strbt r3, [r0], #1) @ May fault
ldrgeb r3, [r1], #1
USER( strgebt r3, [r0], #1) @ May fault
ldrgtb r3, [r1], #0
USER( strgtbt r3, [r0], #1) @ May fault
b .c2u_finished
.section .fixup,"ax"
.align 0
9001: LOADREGS(fd,sp!, {r0, r4 - r7, pc})
.previous
/* Prototype: unsigned long uaccess_user_copy_from_user(void *to,const void *from,unsigned long n);
* Purpose : copy a block from user memory to kernel memory
* Params : to - kernel memory
* : from - user memory
* : n - number of bytes to copy
* Returns : Number of bytes NOT copied.
*/
.cfu_dest_not_aligned:
rsb ip, ip, #4
cmp ip, #2
USER( ldrbt r3, [r1], #1) @ May fault
strb r3, [r0], #1
USER( ldrgebt r3, [r1], #1) @ May fault
strgeb r3, [r0], #1
USER( ldrgtbt r3, [r1], #1) @ May fault
strgtb r3, [r0], #1
sub r2, r2, ip
b .cfu_dest_aligned
ENTRY(uaccess_user_copy_from_user)
stmfd sp!, {r0, r2, r4 - r7, lr}
cmp r2, #4
blt .cfu_not_enough
ands ip, r0, #3
bne .cfu_dest_not_aligned
.cfu_dest_aligned:
ands ip, r1, #3
bne .cfu_src_not_aligned
/*
* Seeing as there has to be at least 8 bytes to copy, we can
* copy one word, and force a user-mode page fault...
*/
.cfu_0fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .cfu_0nowords
USER( ldrt r3, [r1], #4)
str r3, [r0], #4
mov ip, r1, lsl #32 - PAGE_SHIFT @ On each page, use a ld/st??t instruction
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .cfu_0fupi
/*
* ip = max no. of bytes to copy before needing another "strt" insn
*/
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #32
blt .cfu_0rem8lp
.cfu_0cpy8lp: ldmia r1!, {r3 - r6} @ Shouldnt fault
stmia r0!, {r3 - r6}
ldmia r1!, {r3 - r6} @ Shouldnt fault
stmia r0!, {r3 - r6}
subs ip, ip, #32
bpl .cfu_0cpy8lp
.cfu_0rem8lp: cmn ip, #16
ldmgeia r1!, {r3 - r6} @ Shouldnt fault
stmgeia r0!, {r3 - r6}
tst ip, #8
ldmneia r1!, {r3 - r4} @ Shouldnt fault
stmneia r0!, {r3 - r4}
tst ip, #4
ldrnet r3, [r1], #4 @ Shouldnt fault
strne r3, [r0], #4
ands ip, ip, #3
beq .cfu_0fupi
.cfu_0nowords: teq ip, #0
beq .cfu_finished
.cfu_nowords: cmp ip, #2
USER( ldrbt r3, [r1], #1) @ May fault
strb r3, [r0], #1
USER( ldrgebt r3, [r1], #1) @ May fault
strgeb r3, [r0], #1
USER( ldrgtbt r3, [r1], #1) @ May fault
strgtb r3, [r0], #1
b .cfu_finished
.cfu_not_enough:
movs ip, r2
bne .cfu_nowords
.cfu_finished: mov r0, #0
add sp, sp, #8
LOADREGS(fd,sp!,{r4 - r7, pc})
.cfu_src_not_aligned:
bic r1, r1, #3
USER( ldrt r7, [r1], #4) @ May fault
cmp ip, #2
bgt .cfu_3fupi
beq .cfu_2fupi
.cfu_1fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .cfu_1nowords
mov r3, r7, pull #8
USER( ldrt r7, [r1], #4) @ May fault
orr r3, r3, r7, push #24
str r3, [r0], #4
mov ip, r1, lsl #32 - PAGE_SHIFT
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .cfu_1fupi
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #16
blt .cfu_1rem8lp
.cfu_1cpy8lp: mov r3, r7, pull #8
ldmia r1!, {r4 - r7} @ Shouldnt fault
orr r3, r3, r4, push #24
mov r4, r4, pull #8
orr r4, r4, r5, push #24
mov r5, r5, pull #8
orr r5, r5, r6, push #24
mov r6, r6, pull #8
orr r6, r6, r7, push #24
stmia r0!, {r3 - r6}
subs ip, ip, #16
bpl .cfu_1cpy8lp
.cfu_1rem8lp: tst ip, #8
movne r3, r7, pull #8
ldmneia r1!, {r4, r7} @ Shouldnt fault
orrne r3, r3, r4, push #24
movne r4, r4, pull #8
orrne r4, r4, r7, push #24
stmneia r0!, {r3 - r4}
tst ip, #4
movne r3, r7, pull #8
USER( ldrnet r7, [r1], #4) @ May fault
orrne r3, r3, r7, push #24
strne r3, [r0], #4
ands ip, ip, #3
beq .cfu_1fupi
.cfu_1nowords: mov r3, r7, lsr #byte(1)
teq ip, #0
beq .cfu_finished
cmp ip, #2
strb r3, [r0], #1
movge r3, r7, lsr #byte(2)
strgeb r3, [r0], #1
movgt r3, r7, lsr #byte(3)
strgtb r3, [r0], #1
b .cfu_finished
.cfu_2fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .cfu_2nowords
mov r3, r7, pull #16
USER( ldrt r7, [r1], #4) @ May fault
orr r3, r3, r7, push #16
str r3, [r0], #4
mov ip, r1, lsl #32 - PAGE_SHIFT
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .cfu_2fupi
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #16
blt .cfu_2rem8lp
.cfu_2cpy8lp: mov r3, r7, pull #16
ldmia r1!, {r4 - r7} @ Shouldnt fault
orr r3, r3, r4, push #16
mov r4, r4, pull #16
orr r4, r4, r5, push #16
mov r5, r5, pull #16
orr r5, r5, r6, push #16
mov r6, r6, pull #16
orr r6, r6, r7, push #16
stmia r0!, {r3 - r6}
subs ip, ip, #16
bpl .cfu_2cpy8lp
.cfu_2rem8lp: tst ip, #8
movne r3, r7, pull #16
ldmneia r1!, {r4, r7} @ Shouldnt fault
orrne r3, r3, r4, push #16
movne r4, r4, pull #16
orrne r4, r4, r7, push #16
stmneia r0!, {r3 - r4}
tst ip, #4
movne r3, r7, pull #16
USER( ldrnet r7, [r1], #4) @ May fault
orrne r3, r3, r7, push #16
strne r3, [r0], #4
ands ip, ip, #3
beq .cfu_2fupi
.cfu_2nowords: mov r3, r7, lsr #byte(2)
teq ip, #0
beq .cfu_finished
cmp ip, #2
strb r3, [r0], #1
movge r3, r7, lsr #byte(3)
strgeb r3, [r0], #1
USER( ldrgtbt r3, [r1], #0) @ May fault
strgtb r3, [r0], #1
b .cfu_finished
.cfu_3fupi: subs r2, r2, #4
addmi ip, r2, #4
bmi .cfu_3nowords
mov r3, r7, pull #24
USER( ldrt r7, [r1], #4) @ May fault
orr r3, r3, r7, push #8
str r3, [r0], #4
mov ip, r1, lsl #32 - PAGE_SHIFT
rsb ip, ip, #0
movs ip, ip, lsr #32 - PAGE_SHIFT
beq .cfu_3fupi
cmp r2, ip
movlt ip, r2
sub r2, r2, ip
subs ip, ip, #16
blt .cfu_3rem8lp
.cfu_3cpy8lp: mov r3, r7, pull #24
ldmia r1!, {r4 - r7} @ Shouldnt fault
orr r3, r3, r4, push #8
mov r4, r4, pull #24
orr r4, r4, r5, push #8
mov r5, r5, pull #24
orr r5, r5, r6, push #8
mov r6, r6, pull #24
orr r6, r6, r7, push #8
stmia r0!, {r3 - r6}
subs ip, ip, #16
bpl .cfu_3cpy8lp
.cfu_3rem8lp: tst ip, #8
movne r3, r7, pull #24
ldmneia r1!, {r4, r7} @ Shouldnt fault
orrne r3, r3, r4, push #8
movne r4, r4, pull #24
orrne r4, r4, r7, push #8
stmneia r0!, {r3 - r4}
tst ip, #4
movne r3, r7, pull #24
USER( ldrnet r7, [r1], #4) @ May fault
orrne r3, r3, r7, push #8
strne r3, [r0], #4
ands ip, ip, #3
beq .cfu_3fupi
.cfu_3nowords: mov r3, r7, lsr #byte(3)
teq ip, #0
beq .cfu_finished
cmp ip, #2
strb r3, [r0], #1
USER( ldrgebt r3, [r1], #1) @ May fault
strgeb r3, [r0], #1
USER( ldrgtbt r3, [r1], #1) @ May fault
strgtb r3, [r0], #1
b .cfu_finished
.section .fixup,"ax"
.align 0
/*
* We took an exception. r0 contains a pointer to
* the byte not copied.
*/
9001: ldr r2, [sp], #4 @ void *to
sub r2, r0, r2 @ bytes copied
ldr r1, [sp], #4 @ unsigned long count
subs r4, r1, r2 @ bytes left to copy
movne r1, r4
blne __memzero
mov r0, r4
LOADREGS(fd,sp!, {r4 - r7, pc})
.previous
/* Prototype: int uaccess_user_clear_user(void *addr, size_t sz)
* Purpose : clear some user memory
* Params : addr - user memory address to clear
* : sz - number of bytes to clear
* Returns : number of bytes NOT cleared
*/
ENTRY(uaccess_user_clear_user)
stmfd sp!, {r1, lr}
mov r2, #0
cmp r1, #4
blt 2f
ands ip, r0, #3
beq 1f
cmp ip, #2
USER( strbt r2, [r0], #1)
USER( strlebt r2, [r0], #1)
USER( strltbt r2, [r0], #1)
rsb ip, ip, #4
sub r1, r1, ip @ 7 6 5 4 3 2 1
1: subs r1, r1, #8 @ -1 -2 -3 -4 -5 -6 -7
USER( strplt r2, [r0], #4)
USER( strplt r2, [r0], #4)
bpl 1b
adds r1, r1, #4 @ 3 2 1 0 -1 -2 -3
USER( strplt r2, [r0], #4)
2: tst r1, #2 @ 1x 1x 0x 0x 1x 1x 0x
USER( strnebt r2, [r0], #1)
USER( strnebt r2, [r0], #1)
tst r1, #1 @ x1 x0 x1 x0 x1 x0 x1
USER( strnebt r2, [r0], #1)
mov r0, #0
LOADREGS(fd,sp!, {r1, pc})
.section .fixup,"ax"
.align 0
9001: LOADREGS(fd,sp!, {r0, pc})
.previous
/*
* Copy a string from user space to kernel space.
* r0 = dst, r1 = src, r2 = byte length
* returns the number of characters copied (strlen of copied string),
* -EFAULT on exception, or "len" if we fill the whole buffer
*/
ENTRY(uaccess_user_strncpy_from_user)
save_lr
mov ip, r1
1: subs r2, r2, #1
USER( ldrplbt r3, [r1], #1)
bmi 2f
strb r3, [r0], #1
teq r3, #0
bne 1b
sub r1, r1, #1 @ take NUL character out of count
2: sub r0, r1, ip
restore_pc
.section .fixup,"ax"
.align 0
9001: mov r3, #0
strb r3, [r0, #0] @ null terminate
mov r0, #-EFAULT
restore_pc
.previous
/* Prototype: unsigned long uaccess_user_strnlen_user(const char *str, long n)
* Purpose : get length of a string in user memory
* Params : str - address of string in user memory
* Returns : length of string *including terminator*
* or zero on exception, or n + 1 if too long
*/
ENTRY(uaccess_user_strnlen_user)
save_lr
mov r2, r0
1:
USER( ldrbt r3, [r0], #1)
teq r3, #0
beq 2f
subs r1, r1, #1
bne 1b
add r0, r0, #1
2: sub r0, r0, r2
restore_pc
.section .fixup,"ax"
.align 0
9001: mov r0, #0
restore_pc
.previous
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