memclr_arm64.s

Documentation: runtime

     1// Copyright 2014 The Go Authors. All rights reserved.
     2// Use of this source code is governed by a BSD-style
     3// license that can be found in the LICENSE file.
     4
     5#include "textflag.h"
     6
     7// See memclrNoHeapPointers Go doc for important implementation constraints.
     8
     9// func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr)
    10// Also called from assembly in sys_windows_arm64.s without g (but using Go stack convention).
    11TEXT runtime·memclrNoHeapPointers<ABIInternal>(SB),NOSPLIT,$0-16
    12	CMP	$16, R1
    13	// If n is equal to 16 bytes, use zero_exact_16 to zero
    14	BEQ	zero_exact_16
    15
    16	// If n is greater than 16 bytes, use zero_by_16 to zero
    17	BHI	zero_by_16
    18
    19	// n is less than 16 bytes
    20	ADD	R1, R0, R7
    21	TBZ	$3, R1, less_than_8
    22	MOVD	ZR, (R0)
    23	MOVD	ZR, -8(R7)
    24	RET
    25
    26less_than_8:
    27	TBZ	$2, R1, less_than_4
    28	MOVW	ZR, (R0)
    29	MOVW	ZR, -4(R7)
    30	RET
    31
    32less_than_4:
    33	CBZ	R1, ending
    34	MOVB	ZR, (R0)
    35	TBZ	$1, R1, ending
    36	MOVH	ZR, -2(R7)
    37
    38ending:
    39	RET
    40
    41zero_exact_16:
    42	// n is exactly 16 bytes
    43	STP	(ZR, ZR), (R0)
    44	RET
    45
    46zero_by_16:
    47	// n greater than 16 bytes, check if the start address is aligned
    48	NEG	R0, R4
    49	ANDS	$15, R4, R4
    50	// Try zeroing using zva if the start address is aligned with 16
    51	BEQ	try_zva
    52
    53	// Non-aligned store
    54	STP	(ZR, ZR), (R0)
    55	// Make the destination aligned
    56	SUB	R4, R1, R1
    57	ADD	R4, R0, R0
    58	B	try_zva
    59
    60tail_maybe_long:
    61	CMP	$64, R1
    62	BHS	no_zva
    63
    64tail63:
    65	ANDS	$48, R1, R3
    66	BEQ	last16
    67	CMPW	$32, R3
    68	BEQ	last48
    69	BLT	last32
    70	STP.P	(ZR, ZR), 16(R0)
    71last48:
    72	STP.P	(ZR, ZR), 16(R0)
    73last32:
    74	STP.P	(ZR, ZR), 16(R0)
    75	// The last store length is at most 16, so it is safe to use
    76	// stp to write last 16 bytes
    77last16:
    78	ANDS	$15, R1, R1
    79	CBZ	R1, last_end
    80	ADD	R1, R0, R0
    81	STP	(ZR, ZR), -16(R0)
    82last_end:
    83	RET
    84
    85no_zva:
    86	SUB	$16, R0, R0
    87	SUB	$64, R1, R1
    88
    89loop_64:
    90	STP	(ZR, ZR), 16(R0)
    91	STP	(ZR, ZR), 32(R0)
    92	STP	(ZR, ZR), 48(R0)
    93	STP.W	(ZR, ZR), 64(R0)
    94	SUBS	$64, R1, R1
    95	BGE	loop_64
    96	ANDS	$63, R1, ZR
    97	ADD	$16, R0, R0
    98	BNE	tail63
    99	RET
   100
   101try_zva:
   102	// Try using the ZVA feature to zero entire cache lines
   103	// It is not meaningful to use ZVA if the block size is less than 64,
   104	// so make sure that n is greater than or equal to 64
   105	CMP	$63, R1
   106	BLE	tail63
   107
   108	CMP	$128, R1
   109	// Ensure n is at least 128 bytes, so that there is enough to copy after
   110	// alignment.
   111	BLT	no_zva
   112	// Check if ZVA is allowed from user code, and if so get the block size
   113	MOVW	block_size<>(SB), R5
   114	TBNZ	$31, R5, no_zva
   115	CBNZ	R5, zero_by_line
   116	// DCZID_EL0 bit assignments
   117	// [63:5] Reserved
   118	// [4]    DZP, if bit set DC ZVA instruction is prohibited, else permitted
   119	// [3:0]  log2 of the block size in words, eg. if it returns 0x4 then block size is 16 words
   120	MRS	DCZID_EL0, R3
   121	TBZ	$4, R3, init
   122	// ZVA not available
   123	MOVW	$~0, R5
   124	MOVW	R5, block_size<>(SB)
   125	B	no_zva
   126
   127init:
   128	MOVW	$4, R9
   129	ANDW	$15, R3, R5
   130	LSLW	R5, R9, R5
   131	MOVW	R5, block_size<>(SB)
   132
   133	ANDS	$63, R5, R9
   134	// Block size is less than 64.
   135	BNE	no_zva
   136
   137zero_by_line:
   138	CMP	R5, R1
   139	// Not enough memory to reach alignment
   140	BLO	no_zva
   141	SUB	$1, R5, R6
   142	NEG	R0, R4
   143	ANDS	R6, R4, R4
   144	// Already aligned
   145	BEQ	aligned
   146
   147	// check there is enough to copy after alignment
   148	SUB	R4, R1, R3
   149
   150	// Check that the remaining length to ZVA after alignment
   151	// is greater than 64.
   152	CMP	$64, R3
   153	CCMP	GE, R3, R5, $10  // condition code GE, NZCV=0b1010
   154	BLT	no_zva
   155
   156	// We now have at least 64 bytes to zero, update n
   157	MOVD	R3, R1
   158
   159loop_zva_prolog:
   160	STP	(ZR, ZR), (R0)
   161	STP	(ZR, ZR), 16(R0)
   162	STP	(ZR, ZR), 32(R0)
   163	SUBS	$64, R4, R4
   164	STP	(ZR, ZR), 48(R0)
   165	ADD	$64, R0, R0
   166	BGE	loop_zva_prolog
   167
   168	ADD	R4, R0, R0
   169
   170aligned:
   171	SUB	R5, R1, R1
   172
   173loop_zva:
   174	WORD	$0xd50b7420 // DC ZVA, R0
   175	ADD	R5, R0, R0
   176	SUBS	R5, R1, R1
   177	BHS	loop_zva
   178	ANDS	R6, R1, R1
   179	BNE	tail_maybe_long
   180	RET
   181
   182GLOBL block_size<>(SB), NOPTR, $8
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