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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#include "textflag.h"
// See memclrNoHeapPointers Go doc for important implementation constraints.
// func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr)
// Also called from assembly in sys_windows_arm64.s without g (but using Go stack convention).
TEXT runtime·memclrNoHeapPointers(SB),NOSPLIT,$0-16
MOVD ptr+0(FP), R0
MOVD n+8(FP), R1
CMP $16, R1
// If n is equal to 16 bytes, use zero_exact_16 to zero
BEQ zero_exact_16
// If n is greater than 16 bytes, use zero_by_16 to zero
BHI zero_by_16
// n is less than 16 bytes
ADD R1, R0, R7
TBZ $3, R1, less_than_8
MOVD ZR, (R0)
MOVD ZR, -8(R7)
RET
less_than_8:
TBZ $2, R1, less_than_4
MOVW ZR, (R0)
MOVW ZR, -4(R7)
RET
less_than_4:
CBZ R1, ending
MOVB ZR, (R0)
TBZ $1, R1, ending
MOVH ZR, -2(R7)
ending:
RET
zero_exact_16:
// n is exactly 16 bytes
STP (ZR, ZR), (R0)
RET
zero_by_16:
// n greater than 16 bytes, check if the start address is aligned
NEG R0, R4
ANDS $15, R4, R4
// Try zeroing using zva if the start address is aligned with 16
BEQ try_zva
// Non-aligned store
STP (ZR, ZR), (R0)
// Make the destination aligned
SUB R4, R1, R1
ADD R4, R0, R0
B try_zva
tail_maybe_long:
CMP $64, R1
BHS no_zva
tail63:
ANDS $48, R1, R3
BEQ last16
CMPW $32, R3
BEQ last48
BLT last32
STP.P (ZR, ZR), 16(R0)
last48:
STP.P (ZR, ZR), 16(R0)
last32:
STP.P (ZR, ZR), 16(R0)
// The last store length is at most 16, so it is safe to use
// stp to write last 16 bytes
last16:
ANDS $15, R1, R1
CBZ R1, last_end
ADD R1, R0, R0
STP (ZR, ZR), -16(R0)
last_end:
RET
no_zva:
SUB $16, R0, R0
SUB $64, R1, R1
loop_64:
STP (ZR, ZR), 16(R0)
STP (ZR, ZR), 32(R0)
STP (ZR, ZR), 48(R0)
STP.W (ZR, ZR), 64(R0)
SUBS $64, R1, R1
BGE loop_64
ANDS $63, R1, ZR
ADD $16, R0, R0
BNE tail63
RET
try_zva:
// Try using the ZVA feature to zero entire cache lines
// It is not meaningful to use ZVA if the block size is less than 64,
// so make sure that n is greater than or equal to 64
CMP $63, R1
BLE tail63
CMP $128, R1
// Ensure n is at least 128 bytes, so that there is enough to copy after
// alignment.
BLT no_zva
// Check if ZVA is allowed from user code, and if so get the block size
MOVW block_size<>(SB), R5
TBNZ $31, R5, no_zva
CBNZ R5, zero_by_line
// DCZID_EL0 bit assignments
// [63:5] Reserved
// [4] DZP, if bit set DC ZVA instruction is prohibited, else permitted
// [3:0] log2 of the block size in words, eg. if it returns 0x4 then block size is 16 words
MRS DCZID_EL0, R3
TBZ $4, R3, init
// ZVA not available
MOVW $~0, R5
MOVW R5, block_size<>(SB)
B no_zva
init:
MOVW $4, R9
ANDW $15, R3, R5
LSLW R5, R9, R5
MOVW R5, block_size<>(SB)
ANDS $63, R5, R9
// Block size is less than 64.
BNE no_zva
zero_by_line:
CMP R5, R1
// Not enough memory to reach alignment
BLO no_zva
SUB $1, R5, R6
NEG R0, R4
ANDS R6, R4, R4
// Already aligned
BEQ aligned
// check there is enough to copy after alignment
SUB R4, R1, R3
// Check that the remaining length to ZVA after alignment
// is greater than 64.
CMP $64, R3
CCMP GE, R3, R5, $10 // condition code GE, NZCV=0b1010
BLT no_zva
// We now have at least 64 bytes to zero, update n
MOVD R3, R1
loop_zva_prolog:
STP (ZR, ZR), (R0)
STP (ZR, ZR), 16(R0)
STP (ZR, ZR), 32(R0)
SUBS $64, R4, R4
STP (ZR, ZR), 48(R0)
ADD $64, R0, R0
BGE loop_zva_prolog
ADD R4, R0, R0
aligned:
SUB R5, R1, R1
loop_zva:
WORD $0xd50b7420 // DC ZVA, R0
ADD R5, R0, R0
SUBS R5, R1, R1
BHS loop_zva
ANDS R6, R1, R1
BNE tail_maybe_long
RET
GLOBL block_size<>(SB), NOPTR, $8
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