linux/arch/arm64/lib/strncmp.S
Mark Brown 3ac0f4526d arm64: lib: Use modern annotations for assembly functions
In an effort to clarify and simplify the annotation of assembly functions
in the kernel new macros have been introduced. These replace ENTRY and
ENDPROC and also add a new annotation for static functions which previously
had no ENTRY equivalent. Update the annotations in the library code to the
new macros.

Signed-off-by: Mark Brown <broonie@kernel.org>
[will: Use SYM_FUNC_START_WEAK_PI]
Signed-off-by: Will Deacon <will@kernel.org>
2020-01-08 12:23:02 +00:00

300 lines
8.2 KiB
ArmAsm

/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (C) 2013 ARM Ltd.
* Copyright (C) 2013 Linaro.
*
* This code is based on glibc cortex strings work originally authored by Linaro
* be found @
*
* http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
* files/head:/src/aarch64/
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
/*
* compare two strings
*
* Parameters:
* x0 - const string 1 pointer
* x1 - const string 2 pointer
* x2 - the maximal length to be compared
* Returns:
* x0 - an integer less than, equal to, or greater than zero if s1 is found,
* respectively, to be less than, to match, or be greater than s2.
*/
#define REP8_01 0x0101010101010101
#define REP8_7f 0x7f7f7f7f7f7f7f7f
#define REP8_80 0x8080808080808080
/* Parameters and result. */
src1 .req x0
src2 .req x1
limit .req x2
result .req x0
/* Internal variables. */
data1 .req x3
data1w .req w3
data2 .req x4
data2w .req w4
has_nul .req x5
diff .req x6
syndrome .req x7
tmp1 .req x8
tmp2 .req x9
tmp3 .req x10
zeroones .req x11
pos .req x12
limit_wd .req x13
mask .req x14
endloop .req x15
SYM_FUNC_START_WEAK_PI(strncmp)
cbz limit, .Lret0
eor tmp1, src1, src2
mov zeroones, #REP8_01
tst tmp1, #7
b.ne .Lmisaligned8
ands tmp1, src1, #7
b.ne .Lmutual_align
/* Calculate the number of full and partial words -1. */
/*
* when limit is mulitply of 8, if not sub 1,
* the judgement of last dword will wrong.
*/
sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */
/*
* NUL detection works on the principle that (X - 1) & (~X) & 0x80
* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
* can be done in parallel across the entire word.
*/
.Lloop_aligned:
ldr data1, [src1], #8
ldr data2, [src2], #8
.Lstart_realigned:
subs limit_wd, limit_wd, #1
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
eor diff, data1, data2 /* Non-zero if differences found. */
csinv endloop, diff, xzr, pl /* Last Dword or differences.*/
bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
ccmp endloop, #0, #0, eq
b.eq .Lloop_aligned
/*Not reached the limit, must have found the end or a diff. */
tbz limit_wd, #63, .Lnot_limit
/* Limit % 8 == 0 => all bytes significant. */
ands limit, limit, #7
b.eq .Lnot_limit
lsl limit, limit, #3 /* Bits -> bytes. */
mov mask, #~0
CPU_BE( lsr mask, mask, limit )
CPU_LE( lsl mask, mask, limit )
bic data1, data1, mask
bic data2, data2, mask
/* Make sure that the NUL byte is marked in the syndrome. */
orr has_nul, has_nul, mask
.Lnot_limit:
orr syndrome, diff, has_nul
b .Lcal_cmpresult
.Lmutual_align:
/*
* Sources are mutually aligned, but are not currently at an
* alignment boundary. Round down the addresses and then mask off
* the bytes that precede the start point.
* We also need to adjust the limit calculations, but without
* overflowing if the limit is near ULONG_MAX.
*/
bic src1, src1, #7
bic src2, src2, #7
ldr data1, [src1], #8
neg tmp3, tmp1, lsl #3 /* 64 - bits(bytes beyond align). */
ldr data2, [src2], #8
mov tmp2, #~0
sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
/* Big-endian. Early bytes are at MSB. */
CPU_BE( lsl tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */
/* Little-endian. Early bytes are at LSB. */
CPU_LE( lsr tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */
and tmp3, limit_wd, #7
lsr limit_wd, limit_wd, #3
/* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
add limit, limit, tmp1
add tmp3, tmp3, tmp1
orr data1, data1, tmp2
orr data2, data2, tmp2
add limit_wd, limit_wd, tmp3, lsr #3
b .Lstart_realigned
/*when src1 offset is not equal to src2 offset...*/
.Lmisaligned8:
cmp limit, #8
b.lo .Ltiny8proc /*limit < 8... */
/*
* Get the align offset length to compare per byte first.
* After this process, one string's address will be aligned.*/
and tmp1, src1, #7
neg tmp1, tmp1
add tmp1, tmp1, #8
and tmp2, src2, #7
neg tmp2, tmp2
add tmp2, tmp2, #8
subs tmp3, tmp1, tmp2
csel pos, tmp1, tmp2, hi /*Choose the maximum. */
/*
* Here, limit is not less than 8, so directly run .Ltinycmp
* without checking the limit.*/
sub limit, limit, pos
.Ltinycmp:
ldrb data1w, [src1], #1
ldrb data2w, [src2], #1
subs pos, pos, #1
ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */
ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
b.eq .Ltinycmp
cbnz pos, 1f /*find the null or unequal...*/
cmp data1w, #1
ccmp data1w, data2w, #0, cs
b.eq .Lstart_align /*the last bytes are equal....*/
1:
sub result, data1, data2
ret
.Lstart_align:
lsr limit_wd, limit, #3
cbz limit_wd, .Lremain8
/*process more leading bytes to make str1 aligned...*/
ands xzr, src1, #7
b.eq .Lrecal_offset
add src1, src1, tmp3 /*tmp3 is positive in this branch.*/
add src2, src2, tmp3
ldr data1, [src1], #8
ldr data2, [src2], #8
sub limit, limit, tmp3
lsr limit_wd, limit, #3
subs limit_wd, limit_wd, #1
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
eor diff, data1, data2 /* Non-zero if differences found. */
csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
bics has_nul, tmp1, tmp2
ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
b.ne .Lunequal_proc
/*How far is the current str2 from the alignment boundary...*/
and tmp3, tmp3, #7
.Lrecal_offset:
neg pos, tmp3
.Lloopcmp_proc:
/*
* Divide the eight bytes into two parts. First,backwards the src2
* to an alignment boundary,load eight bytes from the SRC2 alignment
* boundary,then compare with the relative bytes from SRC1.
* If all 8 bytes are equal,then start the second part's comparison.
* Otherwise finish the comparison.
* This special handle can garantee all the accesses are in the
* thread/task space in avoid to overrange access.
*/
ldr data1, [src1,pos]
ldr data2, [src2,pos]
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
eor diff, data1, data2 /* Non-zero if differences found. */
csinv endloop, diff, xzr, eq
cbnz endloop, .Lunequal_proc
/*The second part process*/
ldr data1, [src1], #8
ldr data2, [src2], #8
subs limit_wd, limit_wd, #1
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
eor diff, data1, data2 /* Non-zero if differences found. */
csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
bics has_nul, tmp1, tmp2
ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
b.eq .Lloopcmp_proc
.Lunequal_proc:
orr syndrome, diff, has_nul
cbz syndrome, .Lremain8
.Lcal_cmpresult:
/*
* reversed the byte-order as big-endian,then CLZ can find the most
* significant zero bits.
*/
CPU_LE( rev syndrome, syndrome )
CPU_LE( rev data1, data1 )
CPU_LE( rev data2, data2 )
/*
* For big-endian we cannot use the trick with the syndrome value
* as carry-propagation can corrupt the upper bits if the trailing
* bytes in the string contain 0x01.
* However, if there is no NUL byte in the dword, we can generate
* the result directly. We can't just subtract the bytes as the
* MSB might be significant.
*/
CPU_BE( cbnz has_nul, 1f )
CPU_BE( cmp data1, data2 )
CPU_BE( cset result, ne )
CPU_BE( cneg result, result, lo )
CPU_BE( ret )
CPU_BE( 1: )
/* Re-compute the NUL-byte detection, using a byte-reversed value.*/
CPU_BE( rev tmp3, data1 )
CPU_BE( sub tmp1, tmp3, zeroones )
CPU_BE( orr tmp2, tmp3, #REP8_7f )
CPU_BE( bic has_nul, tmp1, tmp2 )
CPU_BE( rev has_nul, has_nul )
CPU_BE( orr syndrome, diff, has_nul )
/*
* The MS-non-zero bit of the syndrome marks either the first bit
* that is different, or the top bit of the first zero byte.
* Shifting left now will bring the critical information into the
* top bits.
*/
clz pos, syndrome
lsl data1, data1, pos
lsl data2, data2, pos
/*
* But we need to zero-extend (char is unsigned) the value and then
* perform a signed 32-bit subtraction.
*/
lsr data1, data1, #56
sub result, data1, data2, lsr #56
ret
.Lremain8:
/* Limit % 8 == 0 => all bytes significant. */
ands limit, limit, #7
b.eq .Lret0
.Ltiny8proc:
ldrb data1w, [src1], #1
ldrb data2w, [src2], #1
subs limit, limit, #1
ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */
ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
b.eq .Ltiny8proc
sub result, data1, data2
ret
.Lret0:
mov result, #0
ret
SYM_FUNC_END_PI(strncmp)
EXPORT_SYMBOL_NOKASAN(strncmp)