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/* strcpy -- copy a nul-terminated string.
Copyright (C) 2013-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library. If not, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
/* Endian independent macros for shifting bytes within registers. */
#ifdef __ARMEB__
#define lsh_gt lsr
#define lsh_ls lsl
#else
#define lsh_gt lsl
#define lsh_ls lsr
#endif
.syntax unified
.text
ENTRY (__stpcpy)
@ Signal stpcpy with NULL in IP.
mov ip, #0
b 0f
END (__stpcpy)
weak_alias (__stpcpy, stpcpy)
libc_hidden_def (__stpcpy)
libc_hidden_builtin_def (stpcpy)
ENTRY (strcpy)
@ Signal strcpy with DEST in IP.
mov ip, r0
0:
pld [r0, #0]
pld [r1, #0]
@ To cater to long strings, we want 8 byte alignment in the source.
@ To cater to small strings, we don't want to start that right away.
@ Loop up to 16 times, less whatever it takes to reach alignment.
and r3, r1, #7
rsb r3, r3, #16
@ Loop until we find ...
1: ldrb r2, [r1], #1
subs r3, r3, #1 @ ... the alignment point
strb r2, [r0], #1
it ne
cmpne r2, #0 @ ... or EOS
bne 1b
@ Disambiguate the exit possibilites above
cmp r2, #0 @ Found EOS
beq .Lreturn
@ Load the next two words asap
ldrd r2, r3, [r1], #8
pld [r0, #64]
pld [r1, #64]
@ For longer strings, we actaully need a stack frame.
push { r4, r5, r6, r7 }
cfi_adjust_cfa_offset (16)
cfi_rel_offset (r4, 0)
cfi_rel_offset (r5, 4)
cfi_rel_offset (r6, 8)
cfi_rel_offset (r7, 12)
@ Subtracting (unsigned saturating) from 1 for any byte means result
@ of 1 for any byte that was originally zero and 0 otherwise.
@ Therefore we consider the lsb of each byte the "found" bit.
#ifdef ARCH_HAS_T2
movw r7, #0x0101
tst r0, #3 @ Test alignment of DEST
movt r7, #0x0101
#else
ldr r7, =0x01010101
tst r0, #3
#endif
bne .Lunaligned
@ So now source (r1) is aligned to 8, and dest (r0) is aligned to 4.
@ Loop, reading 8 bytes at a time, searching for EOS.
.balign 16
2: uqsub8 r4, r7, r2 @ Find EOS
uqsub8 r5, r7, r3
pld [r1, #128]
cmp r4, #0 @ EOS in first word?
pld [r0, #128]
bne 3f
str r2, [r0], #4
cmp r5, #0 @ EOS in second word?
bne 4f
str r3, [r0], #4
ldrd r2, r3, [r1], #8
b 2b
3: sub r1, r1, #4 @ backup to first word
4: sub r1, r1, #4 @ backup to second word
@ ... then finish up any tail a byte at a time.
@ Note that we generally back up and re-read source bytes,
@ but we'll not re-write dest bytes.
.Lbyte_loop:
ldrb r2, [r1], #1
cmp r2, #0
strb r2, [r0], #1
bne .Lbyte_loop
pop { r4, r5, r6, r7 }
cfi_remember_state
cfi_adjust_cfa_offset (-16)
cfi_restore (r4)
cfi_restore (r5)
cfi_restore (r6)
cfi_restore (r7)
.Lreturn:
cmp ip, #0 @ Was this strcpy or stpcpy?
ite eq
subeq r0, r0, #1 @ stpcpy: undo post-inc from store
movne r0, ip @ strcpy: return original dest
bx lr
.Lunaligned:
cfi_restore_state
@ Here, source is aligned to 8, but the destination is not word
@ aligned. Therefore we have to shift the data in order to be
@ able to perform aligned word stores.
@ Find out which misalignment we're dealing with.
tst r0, #1
beq .Lunaligned2
tst r0, #2
bne .Lunaligned3
@ Fallthru to .Lunaligned1.
.macro unaligned_copy unalign
@ Prologue to unaligned loop. Seed shifted non-zero bytes.
uqsub8 r4, r7, r2 @ Find EOS
uqsub8 r5, r7, r3
cmp r4, #0 @ EOS in first word?
it ne
subne r1, r1, #8
bne .Lbyte_loop
#ifdef __ARMEB__
rev r2, r2 @ Byte stores below need LE data
#endif
@ Store a few bytes from the first word.
@ At the same time we align r0 and shift out bytes from r2.
.rept 4-\unalign
strb r2, [r0], #1
lsr r2, r2, #8
.endr
#ifdef __ARMEB__
rev r2, r2 @ Undo previous rev
#endif
@ Rotated unaligned copy loop. The tail of the prologue is
@ shared with the loop itself.
.balign 8
1: cmp r5, #0 @ EOS in second word?
bne 4f
@ Combine first and second words
orr r2, r2, r3, lsh_gt #(\unalign*8)
@ Save leftover bytes from the two words
lsh_ls r6, r3, #((4-\unalign)*8)
str r2, [r0], #4
@ The "real" start of the unaligned copy loop.
ldrd r2, r3, [r1], #8 @ Load 8 more bytes
uqsub8 r4, r7, r2 @ Find EOS
pld [r1, #128]
uqsub8 r5, r7, r3
pld [r0, #128]
cmp r4, #0 @ EOS in first word?
bne 3f
@ Combine the leftover and the first word
orr r6, r6, r2, lsh_gt #(\unalign*8)
@ Discard used bytes from the first word.
lsh_ls r2, r2, #((4-\unalign)*8)
str r6, [r0], #4
b 1b
@ Found EOS in one of the words; adjust backward
3: sub r1, r1, #4
mov r2, r6
4: sub r1, r1, #4
@ And store the remaining bytes from the leftover
#ifdef __ARMEB__
rev r2, r2
#endif
.rept \unalign
strb r2, [r0], #1
lsr r2, r2, #8
.endr
b .Lbyte_loop
.endm
.Lunaligned1:
unaligned_copy 1
.Lunaligned2:
unaligned_copy 2
.Lunaligned3:
unaligned_copy 3
END (strcpy)
libc_hidden_builtin_def (strcpy)
|
