diff --git a/lib/libc/amd64/string/memcmp.S b/lib/libc/amd64/string/memcmp.S index d192229677b3..dc8bcff73cb9 100644 --- a/lib/libc/amd64/string/memcmp.S +++ b/lib/libc/amd64/string/memcmp.S @@ -1,405 +1,420 @@ /*- * Copyright (c) 2018, 2023 The FreeBSD Foundation * * This software was developed by Mateusz Guzik * under sponsorship from the FreeBSD Foundation. * * Portions of this software were developed by Robert Clausecker * under sponsorship from the FreeBSD Foundation. * * 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. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 THE AUTHOR OR CONTRIBUTORS 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 #include #include "amd64_archlevel.h" /* * Note: this routine was written with kernel use in mind (read: no simd), * it is only present in userspace as a temporary measure until something * better gets imported. */ #define ALIGN_TEXT .p2align 4,0x90 /* 16-byte alignment, nop filled */ #ifdef BCMP #define memcmp bcmp #endif ARCHFUNCS(memcmp) ARCHFUNC(memcmp, scalar) ARCHFUNC(memcmp, baseline) ENDARCHFUNCS(memcmp) ARCHENTRY(memcmp, scalar) xorl %eax,%eax 10: cmpq $16,%rdx ja 101632f cmpb $8,%dl jg 100816f cmpb $4,%dl jg 100408f cmpb $2,%dl jge 100204f cmpb $1,%dl jl 100000f movzbl (%rdi),%eax movzbl (%rsi),%r8d subl %r8d,%eax 100000: ret ALIGN_TEXT 100816: movq (%rdi),%r8 movq (%rsi),%r9 cmpq %r8,%r9 jne 80f movq -8(%rdi,%rdx),%r8 movq -8(%rsi,%rdx),%r9 cmpq %r8,%r9 jne 10081608f ret ALIGN_TEXT 100408: movl (%rdi),%r8d movl (%rsi),%r9d cmpl %r8d,%r9d jne 80f movl -4(%rdi,%rdx),%r8d movl -4(%rsi,%rdx),%r9d cmpl %r8d,%r9d jne 10040804f ret ALIGN_TEXT 100204: movzwl (%rdi),%r8d movzwl (%rsi),%r9d cmpl %r8d,%r9d jne 1f movzwl -2(%rdi,%rdx),%r8d movzwl -2(%rsi,%rdx),%r9d cmpl %r8d,%r9d jne 1f ret ALIGN_TEXT 101632: cmpq $32,%rdx ja 103200f movq (%rdi),%r8 movq (%rsi),%r9 cmpq %r8,%r9 jne 80f movq 8(%rdi),%r8 movq 8(%rsi),%r9 cmpq %r8,%r9 jne 10163208f movq -16(%rdi,%rdx),%r8 movq -16(%rsi,%rdx),%r9 cmpq %r8,%r9 jne 10163216f movq -8(%rdi,%rdx),%r8 movq -8(%rsi,%rdx),%r9 cmpq %r8,%r9 jne 10163224f ret ALIGN_TEXT 103200: movq (%rdi),%r8 movq 8(%rdi),%r9 subq (%rsi),%r8 subq 8(%rsi),%r9 orq %r8,%r9 jnz 10320000f movq 16(%rdi),%r8 movq 24(%rdi),%r9 subq 16(%rsi),%r8 subq 24(%rsi),%r9 orq %r8,%r9 jnz 10320016f leaq 32(%rdi),%rdi leaq 32(%rsi),%rsi subq $32,%rdx cmpq $32,%rdx jae 103200b cmpb $0,%dl jne 10b ret /* * Mismatch was found. */ #ifdef BCMP ALIGN_TEXT 10320016: 10320000: 10081608: 10163224: 10163216: 10163208: 10040804: 80: 1: leal 1(%eax),%eax ret #else /* * We need to compute the difference between strings. * Start with narrowing the range down (16 -> 8 -> 4 bytes). */ ALIGN_TEXT 10320016: leaq 16(%rdi),%rdi leaq 16(%rsi),%rsi 10320000: movq (%rdi),%r8 movq (%rsi),%r9 cmpq %r8,%r9 jne 80f leaq 8(%rdi),%rdi leaq 8(%rsi),%rsi jmp 80f ALIGN_TEXT 10081608: 10163224: leaq -8(%rdi,%rdx),%rdi leaq -8(%rsi,%rdx),%rsi jmp 80f ALIGN_TEXT 10163216: leaq -16(%rdi,%rdx),%rdi leaq -16(%rsi,%rdx),%rsi jmp 80f ALIGN_TEXT 10163208: leaq 8(%rdi),%rdi leaq 8(%rsi),%rsi jmp 80f ALIGN_TEXT 10040804: leaq -4(%rdi,%rdx),%rdi leaq -4(%rsi,%rdx),%rsi jmp 1f ALIGN_TEXT 80: movl (%rdi),%r8d movl (%rsi),%r9d cmpl %r8d,%r9d jne 1f leaq 4(%rdi),%rdi leaq 4(%rsi),%rsi /* * We have up to 4 bytes to inspect. */ 1: movzbl (%rdi),%eax movzbl (%rsi),%r8d cmpb %r8b,%al jne 2f movzbl 1(%rdi),%eax movzbl 1(%rsi),%r8d cmpb %r8b,%al jne 2f movzbl 2(%rdi),%eax movzbl 2(%rsi),%r8d cmpb %r8b,%al jne 2f movzbl 3(%rdi),%eax movzbl 3(%rsi),%r8d 2: subl %r8d,%eax ret #endif ARCHEND(memcmp, scalar) ARCHENTRY(memcmp, baseline) cmp $32, %rdx # enough to permit use of the long kernel? ja .Llong test %rdx, %rdx # zero bytes buffer? je .L0 /* * Compare strings of 1--32 bytes. We want to do this by * loading into two xmm registers and then comparing. To avoid * crossing into unmapped pages, we either load 32 bytes from * the start of the buffer or 32 bytes before its end, depending * on whether there is a page boundary between the overread area * or not. */ /* check for page boundaries overreads */ lea 31(%rdi), %eax # end of overread lea 31(%rsi), %r8d lea -1(%rdi, %rdx, 1), %ecx # last character in buffer lea -1(%rsi, %rdx, 1), %r9d xor %ecx, %eax xor %r9d, %r8d test $PAGE_SIZE, %eax # are they on different pages? jz 0f /* fix up rdi */ movdqu -32(%rdi, %rdx, 1), %xmm0 movdqu -16(%rdi, %rdx, 1), %xmm1 lea -8(%rsp), %rdi # end of replacement buffer sub %rdx, %rdi # start of replacement buffer movdqa %xmm0, -40(%rsp) # copy to replacement buffer movdqa %xmm1, -24(%rsp) 0: test $PAGE_SIZE, %r8d jz 0f /* fix up rsi */ movdqu -32(%rsi, %rdx, 1), %xmm0 movdqu -16(%rsi, %rdx, 1), %xmm1 lea -40(%rsp), %rsi # end of replacement buffer sub %rdx, %rsi # start of replacement buffer movdqa %xmm0, -72(%rsp) # copy to replacement buffer movdqa %xmm1, -56(%rsp) /* load data and compare properly */ 0: movdqu 16(%rdi), %xmm1 movdqu 16(%rsi), %xmm3 movdqu (%rdi), %xmm0 movdqu (%rsi), %xmm2 mov %edx, %ecx mov $-1, %edx shl %cl, %rdx # ones where the buffer is not pcmpeqb %xmm3, %xmm1 pcmpeqb %xmm2, %xmm0 pmovmskb %xmm1, %ecx pmovmskb %xmm0, %eax shl $16, %ecx or %ecx, %eax # ones where the buffers match or %edx, %eax # including where the buffer is not not %eax # ones where there is a mismatch #ifndef BCMP bsf %eax, %edx # location of the first mismatch cmovz %eax, %edx # including if there is no mismatch movzbl (%rdi, %rdx, 1), %eax # mismatching bytes movzbl (%rsi, %rdx, 1), %edx sub %edx, %eax #endif ret /* empty input */ .L0: xor %eax, %eax ret /* compare 33+ bytes */ ALIGN_TEXT .Llong: movdqu (%rdi), %xmm0 # load head movdqu (%rsi), %xmm2 mov %rdi, %rcx sub %rdi, %rsi # express rsi as distance from rdi and $~0xf, %rdi # align rdi to 16 bytes movdqu 16(%rsi, %rdi, 1), %xmm1 pcmpeqb 16(%rdi), %xmm1 # compare second half of this iteration add %rcx, %rdx # pointer to last byte in buffer - pcmpeqb %xmm2, %xmm0 + jc .Loverflow # did this overflow? +0: pcmpeqb %xmm2, %xmm0 pmovmskb %xmm0, %eax xor $0xffff, %eax # any mismatch? jne .Lmismatch_head add $64, %rdi # advance to next iteration jmp 1f # and get going with the loop + /* + * If we got here, a buffer length was passed to memcmp(a, b, len) + * such that a + len < a. While this sort of usage is illegal, + * it is plausible that a caller tries to do something like + * memcmp(a, b, SIZE_MAX) if a and b are known to differ, intending + * for memcmp() to stop comparing at the first mismatch. This + * behaviour is not guaranteed by any version of ISO/IEC 9899, + * but usually works out in practice. Let's try to make this + * case work by comparing until the end of the address space. + */ +.Loverflow: + mov $-1, %rdx # compare until the end of memory + jmp 0b + /* process buffer 32 bytes at a time */ ALIGN_TEXT 0: movdqu -32(%rsi, %rdi, 1), %xmm0 movdqu -16(%rsi, %rdi, 1), %xmm1 pcmpeqb -32(%rdi), %xmm0 pcmpeqb -16(%rdi), %xmm1 add $32, %rdi # advance to next iteration 1: pand %xmm0, %xmm1 # 0xff where both halves matched pmovmskb %xmm1, %eax cmp $0xffff, %eax # all bytes matched? jne .Lmismatch cmp %rdx, %rdi # end of buffer reached? jb 0b /* less than 32 bytes left to compare */ movdqu -16(%rdx), %xmm1 # load 32 byte tail through end pointer movdqu -16(%rdx, %rsi, 1), %xmm3 movdqu -32(%rdx), %xmm0 movdqu -32(%rdx, %rsi, 1), %xmm2 pcmpeqb %xmm3, %xmm1 pcmpeqb %xmm2, %xmm0 pmovmskb %xmm1, %ecx pmovmskb %xmm0, %eax shl $16, %ecx or %ecx, %eax # ones where the buffers match not %eax # ones where there is a mismatch #ifndef BCMP bsf %eax, %ecx # location of the first mismatch cmovz %eax, %ecx # including if there is no mismatch add %rcx, %rdx # pointer to potential mismatch movzbl -32(%rdx), %eax # mismatching bytes movzbl -32(%rdx, %rsi, 1), %edx sub %edx, %eax #endif ret #ifdef BCMP .Lmismatch: mov $1, %eax .Lmismatch_head: ret #else /* memcmp */ .Lmismatch_head: tzcnt %eax, %eax # location of mismatch add %rax, %rcx # pointer to mismatch movzbl (%rcx), %eax # mismatching bytes movzbl (%rcx, %rsi, 1), %ecx sub %ecx, %eax ret .Lmismatch: movdqu -48(%rsi, %rdi, 1), %xmm1 pcmpeqb -48(%rdi), %xmm1 # reconstruct xmm1 before PAND pmovmskb %xmm0, %eax # mismatches in first 16 bytes pmovmskb %xmm1, %edx # mismatches in second 16 bytes shl $16, %edx or %edx, %eax # mismatches in both not %eax # matches in both tzcnt %eax, %eax # location of mismatch add %rax, %rdi # pointer to mismatch movzbl -64(%rdi), %eax # mismatching bytes movzbl -64(%rdi, %rsi, 1), %ecx sub %ecx, %eax ret #endif ARCHEND(memcmp, baseline) .section .note.GNU-stack,"",%progbits