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_().

Commit 8f0dc4cfd106 introduces 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...

Fixes: 8f0dc4cfd106 ("riscv: assembler versions of memcpy, memmove, memset") Signed-off-by: Bin Meng bmeng.cn@gmail.com ---

arch/riscv/lib/memcpy.S | 223 ++++++++++++++++++++++++--------------- arch/riscv/lib/memmove.S | 176 ++++++++++++++++++++---------- 2 files changed, 257 insertions(+), 142 deletions(-)

diff --git a/arch/riscv/lib/memcpy.S b/arch/riscv/lib/memcpy.S index 51ab716253..00672c19ad 100644 --- a/arch/riscv/lib/memcpy.S +++ b/arch/riscv/lib/memcpy.S @@ -9,100 +9,151 @@ /* void *memcpy(void *, const void *, size_t) */ ENTRY(__memcpy) WEAK(memcpy) - move t6, a0 /* Preserve return value */ + /* Save for return value */ + mv t6, a0

- /* Defer to byte-oriented copy for small sizes */ - sltiu a3, a2, 128 - bnez a3, 4f - /* Use word-oriented copy only if low-order bits match */ - andi a3, t6, SZREG-1 - andi a4, a1, SZREG-1 - bne a3, a4, 4f + /* + * Register allocation for code below: + * a0 - start of uncopied dst + * a1 - start of uncopied src + * t0 - end of uncopied dst + */ + add t0, a0, a2

- beqz a3, 2f /* Skip if already aligned */ /* - * Round to nearest double word-aligned address - * greater than or equal to start address + * Use bytewise copy if too small. + * + * This threshold must be at least 2*SZREG to ensure at least one + * wordwise copy is performed. It is chosen to be 16 because it will + * save at least 7 iterations of bytewise copy, which pays off the + * fixed overhead. */ - andi a3, a1, ~(SZREG-1) - addi a3, a3, SZREG - /* Handle initial misalignment */ - sub a4, a3, a1 + li a3, 16 + bltu a2, a3, .Lbyte_copy_tail + + /* + * Bytewise copy first to align a0 to word boundary. + */ + addi a2, a0, SZREG-1 + andi a2, a2, ~(SZREG-1) + beq a0, a2, 2f 1: - lb a5, 0(a1) - addi a1, a1, 1 - sb a5, 0(t6) - addi t6, t6, 1 - bltu a1, a3, 1b - sub a2, a2, a4 /* Update count */ + lb a5, 0(a1) + addi a1, a1, 1 + sb a5, 0(a0) + addi a0, a0, 1 + bne a0, a2, 1b +2: + + /* + * Now a0 is word-aligned. If a1 is also word aligned, we could perform + * aligned word-wise copy. Otherwise we need to perform misaligned + * word-wise copy. + */ + andi a3, a1, SZREG-1 + bnez a3, .Lmisaligned_word_copy

+ /* Unrolled wordwise copy */ + addi t0, t0, -(16*SZREG-1) + bgeu a0, t0, 2f +1: + REG_L a2, 0(a1) + REG_L a3, SZREG(a1) + REG_L a4, 2*SZREG(a1) + REG_L a5, 3*SZREG(a1) + REG_L a6, 4*SZREG(a1) + REG_L a7, 5*SZREG(a1) + REG_L t1, 6*SZREG(a1) + REG_L t2, 7*SZREG(a1) + REG_L t3, 8*SZREG(a1) + REG_L t4, 9*SZREG(a1) + REG_L t5, 10*SZREG(a1) + REG_S a2, 0(a0) + REG_S a3, SZREG(a0) + REG_S a4, 2*SZREG(a0) + REG_S a5, 3*SZREG(a0) + REG_S a6, 4*SZREG(a0) + REG_S a7, 5*SZREG(a0) + REG_S t1, 6*SZREG(a0) + REG_S t2, 7*SZREG(a0) + REG_S t3, 8*SZREG(a0) + REG_S t4, 9*SZREG(a0) + REG_S t5, 10*SZREG(a0) + REG_L a2, 11*SZREG(a1) + REG_L a3, 12*SZREG(a1) + REG_L a4, 13*SZREG(a1) + REG_L a5, 14*SZREG(a1) + REG_L a6, 15*SZREG(a1) + addi a1, a1, 16*SZREG + REG_S a2, 11*SZREG(a0) + REG_S a3, 12*SZREG(a0) + REG_S a4, 13*SZREG(a0) + REG_S a5, 14*SZREG(a0) + REG_S a6, 15*SZREG(a0) + addi a0, a0, 16*SZREG + bltu a0, t0, 1b 2: - andi a4, a2, ~((16*SZREG)-1) - beqz a4, 4f - add a3, a1, a4 -3: - REG_L a4, 0(a1) - REG_L a5, SZREG(a1) - REG_L a6, 2*SZREG(a1) - REG_L a7, 3*SZREG(a1) - REG_L t0, 4*SZREG(a1) - REG_L t1, 5*SZREG(a1) - REG_L t2, 6*SZREG(a1) - REG_L t3, 7*SZREG(a1) - REG_L t4, 8*SZREG(a1) - REG_L t5, 9*SZREG(a1) - REG_S a4, 0(t6) - REG_S a5, SZREG(t6) - REG_S a6, 2*SZREG(t6) - REG_S a7, 3*SZREG(t6) - REG_S t0, 4*SZREG(t6) - REG_S t1, 5*SZREG(t6) - REG_S t2, 6*SZREG(t6) - REG_S t3, 7*SZREG(t6) - REG_S t4, 8*SZREG(t6) - REG_S t5, 9*SZREG(t6) - REG_L a4, 10*SZREG(a1) - REG_L a5, 11*SZREG(a1) - REG_L a6, 12*SZREG(a1) - REG_L a7, 13*SZREG(a1) - REG_L t0, 14*SZREG(a1) - REG_L t1, 15*SZREG(a1) - addi a1, a1, 16*SZREG - REG_S a4, 10*SZREG(t6) - REG_S a5, 11*SZREG(t6) - REG_S a6, 12*SZREG(t6) - REG_S a7, 13*SZREG(t6) - REG_S t0, 14*SZREG(t6) - REG_S t1, 15*SZREG(t6) - addi t6, t6, 16*SZREG - bltu a1, a3, 3b - andi a2, a2, (16*SZREG)-1 /* Update count */ - -4: - /* Handle trailing misalignment */ - beqz a2, 6f - add a3, a1, a2 - - /* Use word-oriented copy if co-aligned to word boundary */ - or a5, a1, t6 - or a5, a5, a3 - andi a5, a5, 3 - bnez a5, 5f -7: - lw a4, 0(a1) - addi a1, a1, 4 - sw a4, 0(t6) - addi t6, t6, 4 - bltu a1, a3, 7b + /* Post-loop increment by 16*SZREG-1 and pre-loop decrement by SZREG-1 */ + addi t0, t0, 15*SZREG

- ret + /* Wordwise copy */ + bgeu a0, t0, 2f +1: + REG_L a5, 0(a1) + addi a1, a1, SZREG + REG_S a5, 0(a0) + addi a0, a0, SZREG + bltu a0, t0, 1b +2: + addi t0, t0, SZREG-1

-5: - lb a4, 0(a1) - addi a1, a1, 1 - sb a4, 0(t6) - addi t6, t6, 1 - bltu a1, a3, 5b -6: +.Lbyte_copy_tail: + /* + * Bytewise copy anything left. + */ + beq a0, t0, 2f +1: + lb a5, 0(a1) + addi a1, a1, 1 + sb a5, 0(a0) + addi a0, a0, 1 + bne a0, t0, 1b +2: + + mv a0, t6 ret + +.Lmisaligned_word_copy: + /* + * Misaligned word-wise copy. + * For misaligned copy we still perform word-wise copy, but we need to + * use the value fetched from the previous iteration and do some shifts. + * This is safe because we wouldn't access more words than necessary. + */ + + /* Calculate shifts */ + slli t3, a3, 3 + sub t4, x0, t3 /* negate is okay as shift will only look at LSBs */ + + /* Load the initial value and align a1 */ + andi a1, a1, ~(SZREG-1) + REG_L a5, 0(a1) + + addi t0, t0, -(SZREG-1) + /* At least one iteration will be executed here, no check */ +1: + srl a4, a5, t3 + REG_L a5, SZREG(a1) + addi a1, a1, SZREG + sll a2, a5, t4 + or a2, a2, a4 + REG_S a2, 0(a0) + addi a0, a0, SZREG + bltu a0, t0, 1b + + /* Update pointers to correct value */ + addi t0, t0, SZREG-1 + add a1, a1, a3 + + j .Lbyte_copy_tail END(__memcpy) diff --git a/arch/riscv/lib/memmove.S b/arch/riscv/lib/memmove.S index 07d1d2152b..fbe6701dbe 100644 --- a/arch/riscv/lib/memmove.S +++ b/arch/riscv/lib/memmove.S @@ -5,60 +5,124 @@

ENTRY(__memmove) WEAK(memmove) - move t0, a0 - move t1, a1 - - beq a0, a1, exit_memcpy - beqz a2, exit_memcpy - srli t2, a2, 0x2 - - slt t3, a0, a1 - beqz t3, do_reverse - - andi a2, a2, 0x3 - li t4, 1 - beqz t2, byte_copy - -word_copy: - lw t3, 0(a1) - addi t2, t2, -1 - addi a1, a1, 4 - sw t3, 0(a0) - addi a0, a0, 4 - bnez t2, word_copy - beqz a2, exit_memcpy - j byte_copy - -do_reverse: - add a0, a0, a2 - add a1, a1, a2 - andi a2, a2, 0x3 - li t4, -1 - beqz t2, reverse_byte_copy - -reverse_word_copy: - addi a1, a1, -4 - addi t2, t2, -1 - lw t3, 0(a1) - addi a0, a0, -4 - sw t3, 0(a0) - bnez t2, reverse_word_copy - beqz a2, exit_memcpy - -reverse_byte_copy: - addi a0, a0, -1 - addi a1, a1, -1 - -byte_copy: - lb t3, 0(a1) - addi a2, a2, -1 - sb t3, 0(a0) - add a1, a1, t4 - add a0, a0, t4 - bnez a2, byte_copy - -exit_memcpy: - move a0, t0 - move a1, t1 - ret + /* + * Here we determine if forward copy is possible. Forward copy is + * preferred to backward copy as it is more cache friendly. + * + * If a0 >= a1, t0 gives their distance, if t0 >= a2 then we can + * copy forward. + * If a0 < a1, we can always copy forward. This will make t0 negative, + * so a *unsigned* comparison will always have t0 >= a2. + * + * For forward copy we just delegate the task to memcpy. + */ + sub t0, a0, a1 + bltu t0, a2, 1f + tail __memcpy +1: + + /* + * Register allocation for code below: + * a0 - end of uncopied dst + * a1 - end of uncopied src + * t0 - start of uncopied dst + */ + mv t0, a0 + add a0, a0, a2 + add a1, a1, a2 + + /* + * Use bytewise copy if too small. + * + * This threshold must be at least 2*SZREG to ensure at least one + * wordwise copy is performed. It is chosen to be 16 because it will + * save at least 7 iterations of bytewise copy, which pays off the + * fixed overhead. + */ + li a3, 16 + bltu a2, a3, .Lbyte_copy_tail + + /* + * Bytewise copy first to align t0 to word boundary. + */ + andi a2, a0, ~(SZREG-1) + beq a0, a2, 2f +1: + addi a1, a1, -1 + lb a5, 0(a1) + addi a0, a0, -1 + sb a5, 0(a0) + bne a0, a2, 1b +2: + + /* + * Now a0 is word-aligned. If a1 is also word aligned, we could perform + * aligned word-wise copy. Otherwise we need to perform misaligned + * word-wise copy. + */ + andi a3, a1, SZREG-1 + bnez a3, .Lmisaligned_word_copy + + /* Wordwise copy */ + addi t0, t0, SZREG-1 + bleu a0, t0, 2f +1: + addi a1, a1, -SZREG + REG_L a5, 0(a1) + addi a0, a0, -SZREG + REG_S a5, 0(a0) + bgtu a0, t0, 1b +2: + addi t0, t0, -(SZREG-1) + +.Lbyte_copy_tail: + /* + * Bytewise copy anything left. + */ + beq a0, t0, 2f +1: + addi a1, a1, -1 + lb a5, 0(a1) + addi a0, a0, -1 + sb a5, 0(a0) + bne a0, t0, 1b +2: + + mv a0, t0 + ret + +.Lmisaligned_word_copy: + /* + * Misaligned word-wise copy. + * For misaligned copy we still perform word-wise copy, but we need to + * use the value fetched from the previous iteration and do some shifts. + * This is safe because we wouldn't access more words than necessary. + */ + + /* Calculate shifts */ + slli t3, a3, 3 + sub t4, x0, t3 /* negate is okay as shift will only look at LSBs */ + + /* Load the initial value and align a1 */ + andi a1, a1, ~(SZREG-1) + REG_L a5, 0(a1) + + addi t0, t0, SZREG-1 + /* At least one iteration will be executed here, no check */ +1: + sll a4, a5, t4 + addi a1, a1, -SZREG + REG_L a5, 0(a1) + srl a2, a5, t3 + or a2, a2, a4 + addi a0, a0, -SZREG + REG_S a2, 0(a0) + bgtu a0, t0, 1b + + /* Update pointers to correct value */ + addi t0, t0, -(SZREG-1) + add a1, a1, a3 + + j .Lbyte_copy_tail + END(__memmove)