2024-12-10 00:17:37 +03:00
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From 0a957679a29a06fb2e3971615ff9f05f6becb941 Mon Sep 17 00:00:00 2001
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2024-10-29 05:12:06 +03:00
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From: Eric Biggers <ebiggers@google.com>
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Date: Sun, 13 Oct 2024 21:06:49 -0700
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Subject: crypto: x86/crc32c - simplify code for handling fewer than 200 bytes
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The assembly code in crc32c-pcl-intel-asm_64.S is invoked only for
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lengths >= 512, due to the overhead of saving and restoring FPU state.
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Therefore, it is unnecessary for this code to be excessively "optimized"
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for lengths < 200. Eliminate the excessive unrolling of this part of
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the code and use a more straightforward qword-at-a-time loop.
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Note: the part of the code in question is not entirely redundant, as it
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is still used to process any remainder mod 24, as well as any remaining
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data when fewer than 200 bytes remain after least one 3072-byte chunk.
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Signed-off-by: Eric Biggers <ebiggers@google.com>
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---
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arch/x86/crypto/crc32c-pcl-intel-asm_64.S | 116 ++++++----------------
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1 file changed, 33 insertions(+), 83 deletions(-)
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--- a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
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+++ b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
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@@ -56,20 +56,10 @@
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.quad .Lcrc_\i
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.endm
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-.macro JNC_LESS_THAN j
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- jnc .Lless_than_\j
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-.endm
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-
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-# Define threshold where buffers are considered "small" and routed to more
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-# efficient "by-1" code. This "by-1" code only handles up to 255 bytes, so
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-# SMALL_SIZE can be no larger than 255.
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-
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+# Define threshold below which buffers are considered "small" and routed to
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+# regular CRC code that does not interleave the CRC instructions.
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#define SMALL_SIZE 200
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-.if (SMALL_SIZE > 255)
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-.error "SMALL_ SIZE must be < 256"
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-.endif
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-
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# unsigned int crc_pcl(u8 *buffer, int len, unsigned int crc_init);
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.text
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@@ -100,25 +90,18 @@ SYM_FUNC_START(crc_pcl)
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## Move crc_init for Linux to a different
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mov crc_init_arg, crc_init
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+ mov %bufp, bufptmp # rdi = *buf
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+ cmp $SMALL_SIZE, len
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+ jb .Lsmall
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+
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################################################################
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## 1) ALIGN:
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################################################################
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-
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- mov %bufp, bufptmp # rdi = *buf
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neg %bufp
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and $7, %bufp # calculate the unalignment amount of
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# the address
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je .Lproc_block # Skip if aligned
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- ## If len is less than 8 and we're unaligned, we need to jump
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- ## to special code to avoid reading beyond the end of the buffer
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- cmp $8, len
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- jae .Ldo_align
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- # less_than_8 expects length in upper 3 bits of len_dw
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- # less_than_8_post_shl1 expects length = carryflag * 8 + len_dw[31:30]
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- shl $32-3+1, len_dw
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- jmp .Lless_than_8_post_shl1
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-
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.Ldo_align:
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#### Calculate CRC of unaligned bytes of the buffer (if any)
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movq (bufptmp), tmp # load a quadward from the buffer
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@@ -144,9 +127,6 @@ SYM_FUNC_START(crc_pcl)
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jae .Lfull_block
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.Lcontinue_block:
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- cmpq $SMALL_SIZE, len
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- jb .Lsmall
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-
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## len < 128*24
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movq $2731, %rax # 2731 = ceil(2^16 / 24)
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mul len_dw
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@@ -243,68 +223,38 @@ LABEL crc_ 0
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mov tmp, len
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cmp $128*24, tmp
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jae .Lfull_block
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- cmp $24, tmp
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+ cmp $SMALL_SIZE, tmp
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jae .Lcontinue_block
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-.Lless_than_24:
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- shl $32-4, len_dw # less_than_16 expects length
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- # in upper 4 bits of len_dw
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- jnc .Lless_than_16
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- crc32q (bufptmp), crc_init
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- crc32q 8(bufptmp), crc_init
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- jz .Ldo_return
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- add $16, bufptmp
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- # len is less than 8 if we got here
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- # less_than_8 expects length in upper 3 bits of len_dw
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- # less_than_8_post_shl1 expects length = carryflag * 8 + len_dw[31:30]
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- shl $2, len_dw
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- jmp .Lless_than_8_post_shl1
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-
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#######################################################################
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- ## 6) LESS THAN 256-bytes REMAIN AT THIS POINT (8-bits of len are full)
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+ ## 6) Process any remainder without interleaving:
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#######################################################################
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.Lsmall:
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- shl $32-8, len_dw # Prepare len_dw for less_than_256
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- j=256
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-.rept 5 # j = {256, 128, 64, 32, 16}
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-.altmacro
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-LABEL less_than_ %j # less_than_j: Length should be in
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- # upper lg(j) bits of len_dw
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- j=(j/2)
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- shl $1, len_dw # Get next MSB
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- JNC_LESS_THAN %j
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-.noaltmacro
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- i=0
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-.rept (j/8)
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- crc32q i(bufptmp), crc_init # Compute crc32 of 8-byte data
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- i=i+8
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-.endr
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- jz .Ldo_return # Return if remaining length is zero
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- add $j, bufptmp # Advance buf
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-.endr
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-
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-.Lless_than_8: # Length should be stored in
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- # upper 3 bits of len_dw
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- shl $1, len_dw
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-.Lless_than_8_post_shl1:
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- jnc .Lless_than_4
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- crc32l (bufptmp), crc_init_dw # CRC of 4 bytes
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- jz .Ldo_return # return if remaining data is zero
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- add $4, bufptmp
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-.Lless_than_4: # Length should be stored in
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- # upper 2 bits of len_dw
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- shl $1, len_dw
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- jnc .Lless_than_2
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- crc32w (bufptmp), crc_init_dw # CRC of 2 bytes
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- jz .Ldo_return # return if remaining data is zero
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- add $2, bufptmp
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-.Lless_than_2: # Length should be stored in the MSB
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- # of len_dw
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- shl $1, len_dw
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- jnc .Lless_than_1
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- crc32b (bufptmp), crc_init_dw # CRC of 1 byte
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-.Lless_than_1: # Length should be zero
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-.Ldo_return:
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+ test len, len
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+ jz .Ldone
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+ mov len_dw, %eax
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+ shr $3, %eax
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+ jz .Ldo_dword
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+.Ldo_qwords:
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+ crc32q (bufptmp), crc_init
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+ add $8, bufptmp
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+ dec %eax
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+ jnz .Ldo_qwords
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+.Ldo_dword:
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+ test $4, len_dw
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+ jz .Ldo_word
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+ crc32l (bufptmp), crc_init_dw
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+ add $4, bufptmp
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+.Ldo_word:
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+ test $2, len_dw
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+ jz .Ldo_byte
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+ crc32w (bufptmp), crc_init_dw
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+ add $2, bufptmp
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+.Ldo_byte:
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+ test $1, len_dw
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+ jz .Ldone
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+ crc32b (bufptmp), crc_init_dw
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+.Ldone:
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movq crc_init, %rax
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popq %rsi
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popq %rdi
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