703b84ec29
At present U-Boot SPL fails to boot on SiFive Unleashed board, due to a load address misaligned exception happens when loading the FIT image in spl_load_simple_fit(). The exception happens in memmove() which is called by fdt_splice_(). Commit8f0dc4cfd1introduces an assembly version of memmove but it does take misalignment into account (it checks if length is a multiple of machine word size but pointers need also be aligned). As a result it will generate misaligned load/store for the majority of cases and causes significant performance regression on hardware that traps misaligned load/store and emulate them using firmware. The current behaviour of memcpy is that it checks if both src and dest pointers are co-aligned (aka congruent modular SZ_REG). If aligned, it will copy data word-by-word after first aligning pointers to word boundary. If src and dst are not co-aligned, however, byte-wise copy will be performed. This patch was taken from the Linux kernel patch [1], which has not been applied at the time being. It fixes the memmove and optimises memcpy for misaligned cases. It will first align destination pointer to word-boundary regardless whether src and dest are co-aligned or not. If they indeed are, then wordwise copy is performed. If they are not co-aligned, then it will load two adjacent words from src and use shifts to assemble a full machine word. Some additional assembly level micro-optimisation is also performed to ensure more instructions can be compressed (e.g. prefer a0 to t6). With this patch, U-Boot boots again on SiFive Unleashed board. [1] https://patchwork.kernel.org/project/linux-riscv/patch/20210216225555.4976-1-gary@garyguo.net/ Fixes:8f0dc4cfd1("riscv: assembler versions of memcpy, memmove, memset") Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
160 lines
3.3 KiB
ArmAsm
160 lines
3.3 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2013 Regents of the University of California
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*/
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#include <linux/linkage.h>
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#include <asm/asm.h>
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/* void *memcpy(void *, const void *, size_t) */
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ENTRY(__memcpy)
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WEAK(memcpy)
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/* Save for return value */
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mv t6, a0
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/*
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* Register allocation for code below:
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* a0 - start of uncopied dst
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* a1 - start of uncopied src
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* t0 - end of uncopied dst
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*/
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add t0, a0, a2
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/*
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* Use bytewise copy if too small.
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*
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* This threshold must be at least 2*SZREG to ensure at least one
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* wordwise copy is performed. It is chosen to be 16 because it will
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* save at least 7 iterations of bytewise copy, which pays off the
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* fixed overhead.
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*/
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li a3, 16
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bltu a2, a3, .Lbyte_copy_tail
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/*
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* Bytewise copy first to align a0 to word boundary.
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*/
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addi a2, a0, SZREG-1
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andi a2, a2, ~(SZREG-1)
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beq a0, a2, 2f
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1:
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lb a5, 0(a1)
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addi a1, a1, 1
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sb a5, 0(a0)
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addi a0, a0, 1
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bne a0, a2, 1b
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2:
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/*
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* Now a0 is word-aligned. If a1 is also word aligned, we could perform
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* aligned word-wise copy. Otherwise we need to perform misaligned
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* word-wise copy.
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*/
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andi a3, a1, SZREG-1
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bnez a3, .Lmisaligned_word_copy
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/* Unrolled wordwise copy */
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addi t0, t0, -(16*SZREG-1)
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bgeu a0, t0, 2f
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1:
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REG_L a2, 0(a1)
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REG_L a3, SZREG(a1)
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REG_L a4, 2*SZREG(a1)
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REG_L a5, 3*SZREG(a1)
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REG_L a6, 4*SZREG(a1)
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REG_L a7, 5*SZREG(a1)
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REG_L t1, 6*SZREG(a1)
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REG_L t2, 7*SZREG(a1)
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REG_L t3, 8*SZREG(a1)
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REG_L t4, 9*SZREG(a1)
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REG_L t5, 10*SZREG(a1)
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REG_S a2, 0(a0)
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REG_S a3, SZREG(a0)
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REG_S a4, 2*SZREG(a0)
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REG_S a5, 3*SZREG(a0)
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REG_S a6, 4*SZREG(a0)
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REG_S a7, 5*SZREG(a0)
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REG_S t1, 6*SZREG(a0)
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REG_S t2, 7*SZREG(a0)
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REG_S t3, 8*SZREG(a0)
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REG_S t4, 9*SZREG(a0)
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REG_S t5, 10*SZREG(a0)
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REG_L a2, 11*SZREG(a1)
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REG_L a3, 12*SZREG(a1)
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REG_L a4, 13*SZREG(a1)
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REG_L a5, 14*SZREG(a1)
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REG_L a6, 15*SZREG(a1)
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addi a1, a1, 16*SZREG
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REG_S a2, 11*SZREG(a0)
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REG_S a3, 12*SZREG(a0)
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REG_S a4, 13*SZREG(a0)
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REG_S a5, 14*SZREG(a0)
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REG_S a6, 15*SZREG(a0)
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addi a0, a0, 16*SZREG
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bltu a0, t0, 1b
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2:
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/* Post-loop increment by 16*SZREG-1 and pre-loop decrement by SZREG-1 */
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addi t0, t0, 15*SZREG
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/* Wordwise copy */
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bgeu a0, t0, 2f
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1:
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REG_L a5, 0(a1)
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addi a1, a1, SZREG
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REG_S a5, 0(a0)
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addi a0, a0, SZREG
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bltu a0, t0, 1b
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2:
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addi t0, t0, SZREG-1
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.Lbyte_copy_tail:
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/*
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* Bytewise copy anything left.
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*/
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beq a0, t0, 2f
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1:
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lb a5, 0(a1)
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addi a1, a1, 1
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sb a5, 0(a0)
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addi a0, a0, 1
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bne a0, t0, 1b
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2:
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mv a0, t6
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ret
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.Lmisaligned_word_copy:
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/*
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* Misaligned word-wise copy.
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* For misaligned copy we still perform word-wise copy, but we need to
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* use the value fetched from the previous iteration and do some shifts.
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* This is safe because we wouldn't access more words than necessary.
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*/
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/* Calculate shifts */
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slli t3, a3, 3
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sub t4, x0, t3 /* negate is okay as shift will only look at LSBs */
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/* Load the initial value and align a1 */
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andi a1, a1, ~(SZREG-1)
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REG_L a5, 0(a1)
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addi t0, t0, -(SZREG-1)
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/* At least one iteration will be executed here, no check */
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1:
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srl a4, a5, t3
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REG_L a5, SZREG(a1)
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addi a1, a1, SZREG
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sll a2, a5, t4
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or a2, a2, a4
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REG_S a2, 0(a0)
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addi a0, a0, SZREG
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bltu a0, t0, 1b
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/* Update pointers to correct value */
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addi t0, t0, SZREG-1
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add a1, a1, a3
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j .Lbyte_copy_tail
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END(__memcpy)
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