diff options
Diffstat (limited to 'arch/arm64/lib/strcmp.S')
| -rw-r--r-- | arch/arm64/lib/strcmp.S | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/arch/arm64/lib/strcmp.S b/arch/arm64/lib/strcmp.S new file mode 100644 index 000000000..9b89b4533 --- /dev/null +++ b/arch/arm64/lib/strcmp.S @@ -0,0 +1,190 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (c) 2012-2022, Arm Limited. + * + * Adapted from the original at: + * https://github.com/ARM-software/optimized-routines/blob/189dfefe37d54c5b/string/aarch64/strcmp.S + */ + +#include <linux/linkage.h> +#include <asm/assembler.h> + +/* Assumptions: + * + * ARMv8-a, AArch64. + * MTE compatible. + */ + +#define L(label) .L ## label + +#define REP8_01 0x0101010101010101 +#define REP8_7f 0x7f7f7f7f7f7f7f7f + +#define src1 x0 +#define src2 x1 +#define result x0 + +#define data1 x2 +#define data1w w2 +#define data2 x3 +#define data2w w3 +#define has_nul x4 +#define diff x5 +#define off1 x5 +#define syndrome x6 +#define tmp x6 +#define data3 x7 +#define zeroones x8 +#define shift x9 +#define off2 x10 + +/* On big-endian early bytes are at MSB and on little-endian LSB. + LS_FW means shifting towards early bytes. */ +#ifdef __AARCH64EB__ +# define LS_FW lsl +#else +# define LS_FW lsr +#endif + +/* 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. + Since carry propagation makes 0x1 bytes before a NUL byte appear + NUL too in big-endian, byte-reverse the data before the NUL check. */ + + +SYM_FUNC_START(__pi_strcmp) + sub off2, src2, src1 + mov zeroones, REP8_01 + and tmp, src1, 7 + tst off2, 7 + b.ne L(misaligned8) + cbnz tmp, L(mutual_align) + + .p2align 4 + +L(loop_aligned): + ldr data2, [src1, off2] + ldr data1, [src1], 8 +L(start_realigned): +#ifdef __AARCH64EB__ + rev tmp, data1 + sub has_nul, tmp, zeroones + orr tmp, tmp, REP8_7f +#else + sub has_nul, data1, zeroones + orr tmp, data1, REP8_7f +#endif + bics has_nul, has_nul, tmp /* Non-zero if NUL terminator. */ + ccmp data1, data2, 0, eq + b.eq L(loop_aligned) +#ifdef __AARCH64EB__ + rev has_nul, has_nul +#endif + eor diff, data1, data2 + orr syndrome, diff, has_nul +L(end): +#ifndef __AARCH64EB__ + rev syndrome, syndrome + rev data1, data1 + rev data2, data2 +#endif + clz shift, syndrome + /* The most-significant-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. */ + lsl data1, data1, shift + lsl data2, data2, shift + /* 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 + + .p2align 4 + +L(mutual_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. */ + bic src1, src1, 7 + ldr data2, [src1, off2] + ldr data1, [src1], 8 + neg shift, src2, lsl 3 /* Bits to alignment -64. */ + mov tmp, -1 + LS_FW tmp, tmp, shift + orr data1, data1, tmp + orr data2, data2, tmp + b L(start_realigned) + +L(misaligned8): + /* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always + checking to make sure that we don't access beyond the end of SRC2. */ + cbz tmp, L(src1_aligned) +L(do_misaligned): + ldrb data1w, [src1], 1 + ldrb data2w, [src2], 1 + cmp data1w, 0 + ccmp data1w, data2w, 0, ne /* NZCV = 0b0000. */ + b.ne L(done) + tst src1, 7 + b.ne L(do_misaligned) + +L(src1_aligned): + neg shift, src2, lsl 3 + bic src2, src2, 7 + ldr data3, [src2], 8 +#ifdef __AARCH64EB__ + rev data3, data3 +#endif + lsr tmp, zeroones, shift + orr data3, data3, tmp + sub has_nul, data3, zeroones + orr tmp, data3, REP8_7f + bics has_nul, has_nul, tmp + b.ne L(tail) + + sub off1, src2, src1 + + .p2align 4 + +L(loop_unaligned): + ldr data3, [src1, off1] + ldr data2, [src1, off2] +#ifdef __AARCH64EB__ + rev data3, data3 +#endif + sub has_nul, data3, zeroones + orr tmp, data3, REP8_7f + ldr data1, [src1], 8 + bics has_nul, has_nul, tmp + ccmp data1, data2, 0, eq + b.eq L(loop_unaligned) + + lsl tmp, has_nul, shift +#ifdef __AARCH64EB__ + rev tmp, tmp +#endif + eor diff, data1, data2 + orr syndrome, diff, tmp + cbnz syndrome, L(end) +L(tail): + ldr data1, [src1] + neg shift, shift + lsr data2, data3, shift + lsr has_nul, has_nul, shift +#ifdef __AARCH64EB__ + rev data2, data2 + rev has_nul, has_nul +#endif + eor diff, data1, data2 + orr syndrome, diff, has_nul + b L(end) + +L(done): + sub result, data1, data2 + ret +SYM_FUNC_END(__pi_strcmp) +SYM_FUNC_ALIAS_WEAK(strcmp, __pi_strcmp) +EXPORT_SYMBOL_NOKASAN(strcmp) |