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bionic/libc/arch-arm/krait/bionic/strcmp.S
Elliott Hughes 851e68a240 Unify our assembler macros. 
Our <machine/asm.h> files were modified from upstream, to the extent
that no architecture was actually using the upstream ENTRY or END macros,
assuming that architecture even had such a macro upstream. This patch moves
everyone to the same macros, with just a few tweaks remaining in the
<machine/asm.h> files, which no one should now use directly.

I've removed most of the unused cruft from the <machine/asm.h> files, though
there's still rather a lot in the mips/mips64 ones.

Bug: 12229603
Change-Id: I2fff287dc571ac1087abe9070362fb9420d85d6d
2014-02-20 13:51:26 -08:00

488 lines
15 KiB
ArmAsm
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/*
* Copyright (c) 2013 ARM Ltd
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the company may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <machine/cpu-features.h>
#include <private/bionic_asm.h>
#ifdef __ARMEB__
#define S2LOMEM lsl
#define S2LOMEMEQ lsleq
#define S2HIMEM lsr
#define MSB 0x000000ff
#define LSB 0xff000000
#define BYTE0_OFFSET 24
#define BYTE1_OFFSET 16
#define BYTE2_OFFSET 8
#define BYTE3_OFFSET 0
#else /* not __ARMEB__ */
#define S2LOMEM lsr
#define S2LOMEMEQ lsreq
#define S2HIMEM lsl
#define BYTE0_OFFSET 0
#define BYTE1_OFFSET 8
#define BYTE2_OFFSET 16
#define BYTE3_OFFSET 24
#define MSB 0xff000000
#define LSB 0x000000ff
#endif /* not __ARMEB__ */
.syntax unified
#if defined (__thumb__)
.thumb
.thumb_func
#endif
ENTRY(strcmp)
/* Use LDRD whenever possible. */
/* The main thing to look out for when comparing large blocks is that
the loads do not cross a page boundary when loading past the index
of the byte with the first difference or the first string-terminator.
For example, if the strings are identical and the string-terminator
is at index k, byte by byte comparison will not load beyond address
s1+k and s2+k; word by word comparison may load up to 3 bytes beyond
k; double word - up to 7 bytes. If the load of these bytes crosses
a page boundary, it might cause a memory fault (if the page is not mapped)
that would not have happened in byte by byte comparison.
If an address is (double) word aligned, then a load of a (double) word
from that address will not cross a page boundary.
Therefore, the algorithm below considers word and double-word alignment
of strings separately. */
/* High-level description of the algorithm.
* The fast path: if both strings are double-word aligned,
use LDRD to load two words from each string in every loop iteration.
* If the strings have the same offset from a word boundary,
use LDRB to load and compare byte by byte until
the first string is aligned to a word boundary (at most 3 bytes).
This is optimized for quick return on short unaligned strings.
* If the strings have the same offset from a double-word boundary,
use LDRD to load two words from each string in every loop iteration, as in the fast path.
* If the strings do not have the same offset from a double-word boundary,
load a word from the second string before the loop to initialize the queue.
Use LDRD to load two words from every string in every loop iteration.
Inside the loop, load the second word from the second string only after comparing
the first word, using the queued value, to guarantee safety across page boundaries.
* If the strings do not have the same offset from a word boundary,
use LDR and a shift queue. Order of loads and comparisons matters,
similarly to the previous case.
* Use UADD8 and SEL to compare words, and use REV and CLZ to compute the return value.
* The only difference between ARM and Thumb modes is the use of CBZ instruction.
* The only difference between big and little endian is the use of REV in little endian
to compute the return value, instead of MOV.
*/
.macro m_cbz reg label
#ifdef __thumb2__
cbz \reg, \label
#else /* not defined __thumb2__ */
cmp \reg, #0
beq \label
#endif /* not defined __thumb2__ */
.endm /* m_cbz */
.macro m_cbnz reg label
#ifdef __thumb2__
cbnz \reg, \label
#else /* not defined __thumb2__ */
cmp \reg, #0
bne \label
#endif /* not defined __thumb2__ */
.endm /* m_cbnz */
.macro init
/* Macro to save temporary registers and prepare magic values. */
subs sp, sp, #16
.cfi_def_cfa_offset 16
strd r4, r5, [sp, #8]
.cfi_rel_offset r4, 0
.cfi_rel_offset r5, 4
strd r6, r7, [sp]
.cfi_rel_offset r6, 8
.cfi_rel_offset r7, 12
mvn r6, #0 /* all F */
mov r7, #0 /* all 0 */
.endm /* init */
.macro magic_compare_and_branch w1 w2 label
/* Macro to compare registers w1 and w2 and conditionally branch to label. */
cmp \w1, \w2 /* Are w1 and w2 the same? */
magic_find_zero_bytes \w1
it eq
cmpeq ip, #0 /* Is there a zero byte in w1? */
bne \label
.endm /* magic_compare_and_branch */
.macro magic_find_zero_bytes w1
/* Macro to find all-zero bytes in w1, result is in ip. */
uadd8 ip, \w1, r6
sel ip, r7, r6
.endm /* magic_find_zero_bytes */
.macro setup_return w1 w2
#ifdef __ARMEB__
mov r1, \w1
mov r2, \w2
#else /* not __ARMEB__ */
rev r1, \w1
rev r2, \w2
#endif /* not __ARMEB__ */
.endm /* setup_return */
pld [r0, #0]
pld [r1, #0]
/* Are both strings double-word aligned? */
orr ip, r0, r1
tst ip, #7
bne .L_do_align
/* Fast path. */
.save {r4-r7}
init
.L_doubleword_aligned:
/* Get here when the strings to compare are double-word aligned. */
/* Compare two words in every iteration. */
.p2align 2
2:
pld [r0, #16]
pld [r1, #16]
/* Load the next double-word from each string. */
ldrd r2, r3, [r0], #8
ldrd r4, r5, [r1], #8
magic_compare_and_branch w1=r2, w2=r4, label=.L_return_24
magic_compare_and_branch w1=r3, w2=r5, label=.L_return_35
b 2b
.L_do_align:
/* Is the first string word-aligned? */
ands ip, r0, #3
beq .L_word_aligned_r0
/* Fast compare byte by byte until the first string is word-aligned. */
/* The offset of r0 from a word boundary is in ip. Thus, the number of bytes
to read until the next word boundary is 4-ip. */
bic r0, r0, #3
ldr r2, [r0], #4
lsls ip, ip, #31
beq .L_byte2
bcs .L_byte3
.L_byte1:
ldrb ip, [r1], #1
uxtb r3, r2, ror #BYTE1_OFFSET
subs ip, r3, ip
bne .L_fast_return
m_cbz reg=r3, label=.L_fast_return
.L_byte2:
ldrb ip, [r1], #1
uxtb r3, r2, ror #BYTE2_OFFSET
subs ip, r3, ip
bne .L_fast_return
m_cbz reg=r3, label=.L_fast_return
.L_byte3:
ldrb ip, [r1], #1
uxtb r3, r2, ror #BYTE3_OFFSET
subs ip, r3, ip
bne .L_fast_return
m_cbnz reg=r3, label=.L_word_aligned_r0
.L_fast_return:
mov r0, ip
bx lr
.L_word_aligned_r0:
init
/* The first string is word-aligned. */
/* Is the second string word-aligned? */
ands ip, r1, #3
bne .L_strcmp_unaligned
.L_word_aligned:
/* The strings are word-aligned. */
/* Is the first string double-word aligned? */
tst r0, #4
beq .L_doubleword_aligned_r0
/* If r0 is not double-word aligned yet, align it by loading
and comparing the next word from each string. */
ldr r2, [r0], #4
ldr r4, [r1], #4
magic_compare_and_branch w1=r2 w2=r4 label=.L_return_24
.L_doubleword_aligned_r0:
/* Get here when r0 is double-word aligned. */
/* Is r1 doubleword_aligned? */
tst r1, #4
beq .L_doubleword_aligned
/* Get here when the strings to compare are word-aligned,
r0 is double-word aligned, but r1 is not double-word aligned. */
/* Initialize the queue. */
ldr r5, [r1], #4
/* Compare two words in every iteration. */
.p2align 2
3:
pld [r0, #16]
pld [r1, #16]
/* Load the next double-word from each string and compare. */
ldrd r2, r3, [r0], #8
magic_compare_and_branch w1=r2 w2=r5 label=.L_return_25
ldrd r4, r5, [r1], #8
magic_compare_and_branch w1=r3 w2=r4 label=.L_return_34
b 3b
.macro miscmp_word offsetlo offsethi
/* Macro to compare misaligned strings. */
/* r0, r1 are word-aligned, and at least one of the strings
is not double-word aligned. */
/* Compare one word in every loop iteration. */
/* OFFSETLO is the original bit-offset of r1 from a word-boundary,
OFFSETHI is 32 - OFFSETLO (i.e., offset from the next word). */
/* Initialize the shift queue. */
ldr r5, [r1], #4
/* Compare one word from each string in every loop iteration. */
.p2align 2
7:
ldr r3, [r0], #4
S2LOMEM r5, r5, #\offsetlo
magic_find_zero_bytes w1=r3
cmp r7, ip, S2HIMEM #\offsetlo
and r2, r3, r6, S2LOMEM #\offsetlo
it eq
cmpeq r2, r5
bne .L_return_25
ldr r5, [r1], #4
cmp ip, #0
eor r3, r2, r3
S2HIMEM r2, r5, #\offsethi
it eq
cmpeq r3, r2
bne .L_return_32
b 7b
.endm /* miscmp_word */
.L_strcmp_unaligned:
/* r0 is word-aligned, r1 is at offset ip from a word. */
/* Align r1 to the (previous) word-boundary. */
bic r1, r1, #3
/* Unaligned comparison word by word using LDRs. */
cmp ip, #2
beq .L_miscmp_word_16 /* If ip == 2. */
bge .L_miscmp_word_24 /* If ip == 3. */
miscmp_word offsetlo=8 offsethi=24 /* If ip == 1. */
.L_miscmp_word_24: miscmp_word offsetlo=24 offsethi=8
.L_return_32:
setup_return w1=r3, w2=r2
b .L_do_return
.L_return_34:
setup_return w1=r3, w2=r4
b .L_do_return
.L_return_25:
setup_return w1=r2, w2=r5
b .L_do_return
.L_return_35:
setup_return w1=r3, w2=r5
b .L_do_return
.L_return_24:
setup_return w1=r2, w2=r4
.L_do_return:
#ifdef __ARMEB__
mov r0, ip
#else /* not __ARMEB__ */
rev r0, ip
#endif /* not __ARMEB__ */
/* Restore temporaries early, before computing the return value. */
ldrd r6, r7, [sp]
ldrd r4, r5, [sp, #8]
adds sp, sp, #16
.cfi_def_cfa_offset 0
.cfi_restore r4
.cfi_restore r5
.cfi_restore r6
.cfi_restore r7
/* There is a zero or a different byte between r1 and r2. */
/* r0 contains a mask of all-zero bytes in r1. */
/* Using r0 and not ip here because cbz requires low register. */
m_cbz reg=r0, label=.L_compute_return_value
clz r0, r0
/* r0 contains the number of bits on the left of the first all-zero byte in r1. */
rsb r0, r0, #24
/* Here, r0 contains the number of bits on the right of the first all-zero byte in r1. */
lsr r1, r1, r0
lsr r2, r2, r0
.L_compute_return_value:
movs r0, #1
cmp r1, r2
/* The return value is computed as follows.
If r1>r2 then (C==1 and Z==0) and LS doesn't hold and r0 is #1 at return.
If r1<r2 then (C==0 and Z==0) and we execute SBC with carry_in=0,
which means r0:=r0-r0-1 and r0 is #-1 at return.
If r1=r2 then (C==1 and Z==1) and we execute SBC with carry_in=1,
which means r0:=r0-r0 and r0 is #0 at return.
(C==0 and Z==1) cannot happen because the carry bit is "not borrow". */
it ls
sbcls r0, r0, r0
bx lr
/* The code from the previous version of strcmp.S handles this
* particular case (the second string is 2 bytes off a word alignment)
* faster than any current version. In this very specific case, use the
* previous version. See bionic/libc/arch-arm/cortex-a15/bionic/strcmp.S
* for the unedited version of this code.
*/
.L_miscmp_word_16:
wp1 .req r0
wp2 .req r1
b1 .req r2
w1 .req r4
w2 .req r5
t1 .req ip
@ r3 is scratch
/* At this point, wp1 (r0) has already been word-aligned. */
2:
mov b1, #1
orr b1, b1, b1, lsl #8
orr b1, b1, b1, lsl #16
and t1, wp2, #3
bic wp2, wp2, #3
ldr w1, [wp1], #4
ldr w2, [wp2], #4
/* Critical inner Loop: Block with 2 bytes initial overlap */
.p2align 2
2:
S2HIMEM t1, w1, #16
sub r3, w1, b1
S2LOMEM t1, t1, #16
bic r3, r3, w1
cmp t1, w2, S2LOMEM #16
bne 4f
ands r3, r3, b1, lsl #7
it eq
ldreq w2, [wp2], #4
bne 5f
eor t1, t1, w1
cmp t1, w2, S2HIMEM #16
bne 6f
ldr w1, [wp1], #4
b 2b
5:
#ifdef __ARMEB__
/* The syndrome value may contain false ones if the string ends
* with the bytes 0x01 0x00
*/
tst w1, #0xff000000
it ne
tstne w1, #0x00ff0000
beq 7f
#else
lsls r3, r3, #16
bne 7f
#endif
ldrh w2, [wp2]
S2LOMEM t1, w1, #16
#ifdef __ARMEB__
lsl w2, w2, #16
#endif
b 8f
6:
S2HIMEM w2, w2, #16
S2LOMEM t1, w1, #16
4:
S2LOMEM w2, w2, #16
b 8f
7:
mov r0, #0
/* Restore registers and stack. */
ldrd r6, r7, [sp]
ldrd r4, r5, [sp, #8]
adds sp, sp, #16
.cfi_def_cfa_offset 0
.cfi_restore r4
.cfi_restore r5
.cfi_restore r6
.cfi_restore r7
bx lr
8:
and r2, t1, #LSB
and r0, w2, #LSB
cmp r0, #1
it cs
cmpcs r0, r2
itt eq
S2LOMEMEQ t1, t1, #8
S2LOMEMEQ w2, w2, #8
beq 8b
sub r0, r2, r0
/* Restore registers and stack. */
ldrd r6, r7, [sp]
ldrd r4, r5, [sp, #8]
adds sp, sp, #16
.cfi_def_cfa_offset 0
.cfi_restore r4
.cfi_restore r5
.cfi_restore r6
.cfi_restore r7
bx lr
END(strcmp)
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