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Diffstat (limited to '')
| -rw-r--r-- | arch/riscv/lib/memmove.S | 316 |
1 files changed, 316 insertions, 0 deletions
diff --git a/arch/riscv/lib/memmove.S b/arch/riscv/lib/memmove.S new file mode 100644 index 000000000..e0609e1f0 --- /dev/null +++ b/arch/riscv/lib/memmove.S @@ -0,0 +1,316 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2022 Michael T. Kloos <michael@michaelkloos.com> + */ + +#include <linux/linkage.h> +#include <asm/asm.h> + +SYM_FUNC_START(__memmove) +SYM_FUNC_START_WEAK(memmove) + /* + * Returns + * a0 - dest + * + * Parameters + * a0 - Inclusive first byte of dest + * a1 - Inclusive first byte of src + * a2 - Length of copy n + * + * Because the return matches the parameter register a0, + * we will not clobber or modify that register. + * + * Note: This currently only works on little-endian. + * To port to big-endian, reverse the direction of shifts + * in the 2 misaligned fixup copy loops. + */ + + /* Return if nothing to do */ + beq a0, a1, return_from_memmove + beqz a2, return_from_memmove + + /* + * Register Uses + * Forward Copy: a1 - Index counter of src + * Reverse Copy: a4 - Index counter of src + * Forward Copy: t3 - Index counter of dest + * Reverse Copy: t4 - Index counter of dest + * Both Copy Modes: t5 - Inclusive first multibyte/aligned of dest + * Both Copy Modes: t6 - Non-Inclusive last multibyte/aligned of dest + * Both Copy Modes: t0 - Link / Temporary for load-store + * Both Copy Modes: t1 - Temporary for load-store + * Both Copy Modes: t2 - Temporary for load-store + * Both Copy Modes: a5 - dest to src alignment offset + * Both Copy Modes: a6 - Shift ammount + * Both Copy Modes: a7 - Inverse Shift ammount + * Both Copy Modes: a2 - Alternate breakpoint for unrolled loops + */ + + /* + * Solve for some register values now. + * Byte copy does not need t5 or t6. + */ + mv t3, a0 + add t4, a0, a2 + add a4, a1, a2 + + /* + * Byte copy if copying less than (2 * SZREG) bytes. This can + * cause problems with the bulk copy implementation and is + * small enough not to bother. + */ + andi t0, a2, -(2 * SZREG) + beqz t0, byte_copy + + /* + * Now solve for t5 and t6. + */ + andi t5, t3, -SZREG + andi t6, t4, -SZREG + /* + * If dest(Register t3) rounded down to the nearest naturally + * aligned SZREG address, does not equal dest, then add SZREG + * to find the low-bound of SZREG alignment in the dest memory + * region. Note that this could overshoot the dest memory + * region if n is less than SZREG. This is one reason why + * we always byte copy if n is less than SZREG. + * Otherwise, dest is already naturally aligned to SZREG. + */ + beq t5, t3, 1f + addi t5, t5, SZREG + 1: + + /* + * If the dest and src are co-aligned to SZREG, then there is + * no need for the full rigmarole of a full misaligned fixup copy. + * Instead, do a simpler co-aligned copy. + */ + xor t0, a0, a1 + andi t1, t0, (SZREG - 1) + beqz t1, coaligned_copy + /* Fall through to misaligned fixup copy */ + +misaligned_fixup_copy: + bltu a1, a0, misaligned_fixup_copy_reverse + +misaligned_fixup_copy_forward: + jal t0, byte_copy_until_aligned_forward + + andi a5, a1, (SZREG - 1) /* Find the alignment offset of src (a1) */ + slli a6, a5, 3 /* Multiply by 8 to convert that to bits to shift */ + sub a5, a1, t3 /* Find the difference between src and dest */ + andi a1, a1, -SZREG /* Align the src pointer */ + addi a2, t6, SZREG /* The other breakpoint for the unrolled loop*/ + + /* + * Compute The Inverse Shift + * a7 = XLEN - a6 = XLEN + -a6 + * 2s complement negation to find the negative: -a6 = ~a6 + 1 + * Add that to XLEN. XLEN = SZREG * 8. + */ + not a7, a6 + addi a7, a7, (SZREG * 8 + 1) + + /* + * Fix Misalignment Copy Loop - Forward + * load_val0 = load_ptr[0]; + * do { + * load_val1 = load_ptr[1]; + * store_ptr += 2; + * store_ptr[0 - 2] = (load_val0 >> {a6}) | (load_val1 << {a7}); + * + * if (store_ptr == {a2}) + * break; + * + * load_val0 = load_ptr[2]; + * load_ptr += 2; + * store_ptr[1 - 2] = (load_val1 >> {a6}) | (load_val0 << {a7}); + * + * } while (store_ptr != store_ptr_end); + * store_ptr = store_ptr_end; + */ + + REG_L t0, (0 * SZREG)(a1) + 1: + REG_L t1, (1 * SZREG)(a1) + addi t3, t3, (2 * SZREG) + srl t0, t0, a6 + sll t2, t1, a7 + or t2, t0, t2 + REG_S t2, ((0 * SZREG) - (2 * SZREG))(t3) + + beq t3, a2, 2f + + REG_L t0, (2 * SZREG)(a1) + addi a1, a1, (2 * SZREG) + srl t1, t1, a6 + sll t2, t0, a7 + or t2, t1, t2 + REG_S t2, ((1 * SZREG) - (2 * SZREG))(t3) + + bne t3, t6, 1b + 2: + mv t3, t6 /* Fix the dest pointer in case the loop was broken */ + + add a1, t3, a5 /* Restore the src pointer */ + j byte_copy_forward /* Copy any remaining bytes */ + +misaligned_fixup_copy_reverse: + jal t0, byte_copy_until_aligned_reverse + + andi a5, a4, (SZREG - 1) /* Find the alignment offset of src (a4) */ + slli a6, a5, 3 /* Multiply by 8 to convert that to bits to shift */ + sub a5, a4, t4 /* Find the difference between src and dest */ + andi a4, a4, -SZREG /* Align the src pointer */ + addi a2, t5, -SZREG /* The other breakpoint for the unrolled loop*/ + + /* + * Compute The Inverse Shift + * a7 = XLEN - a6 = XLEN + -a6 + * 2s complement negation to find the negative: -a6 = ~a6 + 1 + * Add that to XLEN. XLEN = SZREG * 8. + */ + not a7, a6 + addi a7, a7, (SZREG * 8 + 1) + + /* + * Fix Misalignment Copy Loop - Reverse + * load_val1 = load_ptr[0]; + * do { + * load_val0 = load_ptr[-1]; + * store_ptr -= 2; + * store_ptr[1] = (load_val0 >> {a6}) | (load_val1 << {a7}); + * + * if (store_ptr == {a2}) + * break; + * + * load_val1 = load_ptr[-2]; + * load_ptr -= 2; + * store_ptr[0] = (load_val1 >> {a6}) | (load_val0 << {a7}); + * + * } while (store_ptr != store_ptr_end); + * store_ptr = store_ptr_end; + */ + + REG_L t1, ( 0 * SZREG)(a4) + 1: + REG_L t0, (-1 * SZREG)(a4) + addi t4, t4, (-2 * SZREG) + sll t1, t1, a7 + srl t2, t0, a6 + or t2, t1, t2 + REG_S t2, ( 1 * SZREG)(t4) + + beq t4, a2, 2f + + REG_L t1, (-2 * SZREG)(a4) + addi a4, a4, (-2 * SZREG) + sll t0, t0, a7 + srl t2, t1, a6 + or t2, t0, t2 + REG_S t2, ( 0 * SZREG)(t4) + + bne t4, t5, 1b + 2: + mv t4, t5 /* Fix the dest pointer in case the loop was broken */ + + add a4, t4, a5 /* Restore the src pointer */ + j byte_copy_reverse /* Copy any remaining bytes */ + +/* + * Simple copy loops for SZREG co-aligned memory locations. + * These also make calls to do byte copies for any unaligned + * data at their terminations. + */ +coaligned_copy: + bltu a1, a0, coaligned_copy_reverse + +coaligned_copy_forward: + jal t0, byte_copy_until_aligned_forward + + 1: + REG_L t1, ( 0 * SZREG)(a1) + addi a1, a1, SZREG + addi t3, t3, SZREG + REG_S t1, (-1 * SZREG)(t3) + bne t3, t6, 1b + + j byte_copy_forward /* Copy any remaining bytes */ + +coaligned_copy_reverse: + jal t0, byte_copy_until_aligned_reverse + + 1: + REG_L t1, (-1 * SZREG)(a4) + addi a4, a4, -SZREG + addi t4, t4, -SZREG + REG_S t1, ( 0 * SZREG)(t4) + bne t4, t5, 1b + + j byte_copy_reverse /* Copy any remaining bytes */ + +/* + * These are basically sub-functions within the function. They + * are used to byte copy until the dest pointer is in alignment. + * At which point, a bulk copy method can be used by the + * calling code. These work on the same registers as the bulk + * copy loops. Therefore, the register values can be picked + * up from where they were left and we avoid code duplication + * without any overhead except the call in and return jumps. + */ +byte_copy_until_aligned_forward: + beq t3, t5, 2f + 1: + lb t1, 0(a1) + addi a1, a1, 1 + addi t3, t3, 1 + sb t1, -1(t3) + bne t3, t5, 1b + 2: + jalr zero, 0x0(t0) /* Return to multibyte copy loop */ + +byte_copy_until_aligned_reverse: + beq t4, t6, 2f + 1: + lb t1, -1(a4) + addi a4, a4, -1 + addi t4, t4, -1 + sb t1, 0(t4) + bne t4, t6, 1b + 2: + jalr zero, 0x0(t0) /* Return to multibyte copy loop */ + +/* + * Simple byte copy loops. + * These will byte copy until they reach the end of data to copy. + * At that point, they will call to return from memmove. + */ +byte_copy: + bltu a1, a0, byte_copy_reverse + +byte_copy_forward: + beq t3, t4, 2f + 1: + lb t1, 0(a1) + addi a1, a1, 1 + addi t3, t3, 1 + sb t1, -1(t3) + bne t3, t4, 1b + 2: + ret + +byte_copy_reverse: + beq t4, t3, 2f + 1: + lb t1, -1(a4) + addi a4, a4, -1 + addi t4, t4, -1 + sb t1, 0(t4) + bne t4, t3, 1b + 2: + +return_from_memmove: + ret + +SYM_FUNC_END(memmove) +SYM_FUNC_END(__memmove) |