memclr_arm64.s

     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).
    11  TEXT runtime·memclrNoHeapPointers<ABIInternal>(SB),NOSPLIT,$0-16
    12  #ifndef GOEXPERIMENT_regabiargs
    13  	MOVD	ptr+0(FP), R0
    14  	MOVD	n+8(FP), R1
    15  #endif
    16  
    17  	CMP	$16, R1
    18  	// If n is equal to 16 bytes, use zero_exact_16 to zero
    19  	BEQ	zero_exact_16
    20  
    21  	// If n is greater than 16 bytes, use zero_by_16 to zero
    22  	BHI	zero_by_16
    23  
    24  	// n is less than 16 bytes
    25  	ADD	R1, R0, R7
    26  	TBZ	$3, R1, less_than_8
    27  	MOVD	ZR, (R0)
    28  	MOVD	ZR, -8(R7)
    29  	RET
    30  
    31  less_than_8:
    32  	TBZ	$2, R1, less_than_4
    33  	MOVW	ZR, (R0)
    34  	MOVW	ZR, -4(R7)
    35  	RET
    36  
    37  less_than_4:
    38  	CBZ	R1, ending
    39  	MOVB	ZR, (R0)
    40  	TBZ	$1, R1, ending
    41  	MOVH	ZR, -2(R7)
    42  
    43  ending:
    44  	RET
    45  
    46  zero_exact_16:
    47  	// n is exactly 16 bytes
    48  	STP	(ZR, ZR), (R0)
    49  	RET
    50  
    51  zero_by_16:
    52  	// n greater than 16 bytes, check if the start address is aligned
    53  	NEG	R0, R4
    54  	ANDS	$15, R4, R4
    55  	// Try zeroing using zva if the start address is aligned with 16
    56  	BEQ	try_zva
    57  
    58  	// Non-aligned store
    59  	STP	(ZR, ZR), (R0)
    60  	// Make the destination aligned
    61  	SUB	R4, R1, R1
    62  	ADD	R4, R0, R0
    63  	B	try_zva
    64  
    65  tail_maybe_long:
    66  	CMP	$64, R1
    67  	BHS	no_zva
    68  
    69  tail63:
    70  	ANDS	$48, R1, R3
    71  	BEQ	last16
    72  	CMPW	$32, R3
    73  	BEQ	last48
    74  	BLT	last32
    75  	STP.P	(ZR, ZR), 16(R0)
    76  last48:
    77  	STP.P	(ZR, ZR), 16(R0)
    78  last32:
    79  	STP.P	(ZR, ZR), 16(R0)
    80  	// The last store length is at most 16, so it is safe to use
    81  	// stp to write last 16 bytes
    82  last16:
    83  	ANDS	$15, R1, R1
    84  	CBZ	R1, last_end
    85  	ADD	R1, R0, R0
    86  	STP	(ZR, ZR), -16(R0)
    87  last_end:
    88  	RET
    89  
    90  no_zva:
    91  	SUB	$16, R0, R0
    92  	SUB	$64, R1, R1
    93  
    94  loop_64:
    95  	STP	(ZR, ZR), 16(R0)
    96  	STP	(ZR, ZR), 32(R0)
    97  	STP	(ZR, ZR), 48(R0)
    98  	STP.W	(ZR, ZR), 64(R0)
    99  	SUBS	$64, R1, R1
   100  	BGE	loop_64
   101  	ANDS	$63, R1, ZR
   102  	ADD	$16, R0, R0
   103  	BNE	tail63
   104  	RET
   105  
   106  try_zva:
   107  	// Try using the ZVA feature to zero entire cache lines
   108  	// It is not meaningful to use ZVA if the block size is less than 64,
   109  	// so make sure that n is greater than or equal to 64
   110  	CMP	$63, R1
   111  	BLE	tail63
   112  
   113  	CMP	$128, R1
   114  	// Ensure n is at least 128 bytes, so that there is enough to copy after
   115  	// alignment.
   116  	BLT	no_zva
   117  	// Check if ZVA is allowed from user code, and if so get the block size
   118  	MOVW	block_size<>(SB), R5
   119  	TBNZ	$31, R5, no_zva
   120  	CBNZ	R5, zero_by_line
   121  	// DCZID_EL0 bit assignments
   122  	// [63:5] Reserved
   123  	// [4]    DZP, if bit set DC ZVA instruction is prohibited, else permitted
   124  	// [3:0]  log2 of the block size in words, eg. if it returns 0x4 then block size is 16 words
   125  	MRS	DCZID_EL0, R3
   126  	TBZ	$4, R3, init
   127  	// ZVA not available
   128  	MOVW	$~0, R5
   129  	MOVW	R5, block_size<>(SB)
   130  	B	no_zva
   131  
   132  init:
   133  	MOVW	$4, R9
   134  	ANDW	$15, R3, R5
   135  	LSLW	R5, R9, R5
   136  	MOVW	R5, block_size<>(SB)
   137  
   138  	ANDS	$63, R5, R9
   139  	// Block size is less than 64.
   140  	BNE	no_zva
   141  
   142  zero_by_line:
   143  	CMP	R5, R1
   144  	// Not enough memory to reach alignment
   145  	BLO	no_zva
   146  	SUB	$1, R5, R6
   147  	NEG	R0, R4
   148  	ANDS	R6, R4, R4
   149  	// Already aligned
   150  	BEQ	aligned
   151  
   152  	// check there is enough to copy after alignment
   153  	SUB	R4, R1, R3
   154  
   155  	// Check that the remaining length to ZVA after alignment
   156  	// is greater than 64.
   157  	CMP	$64, R3
   158  	CCMP	GE, R3, R5, $10  // condition code GE, NZCV=0b1010
   159  	BLT	no_zva
   160  
   161  	// We now have at least 64 bytes to zero, update n
   162  	MOVD	R3, R1
   163  
   164  loop_zva_prolog:
   165  	STP	(ZR, ZR), (R0)
   166  	STP	(ZR, ZR), 16(R0)
   167  	STP	(ZR, ZR), 32(R0)
   168  	SUBS	$64, R4, R4
   169  	STP	(ZR, ZR), 48(R0)
   170  	ADD	$64, R0, R0
   171  	BGE	loop_zva_prolog
   172  
   173  	ADD	R4, R0, R0
   174  
   175  aligned:
   176  	SUB	R5, R1, R1
   177  
   178  loop_zva:
   179  	WORD	$0xd50b7420 // DC ZVA, R0
   180  	ADD	R5, R0, R0
   181  	SUBS	R5, R1, R1
   182  	BHS	loop_zva
   183  	ANDS	R6, R1, R1
   184  	BNE	tail_maybe_long
   185  	RET
   186  
   187  GLOBL block_size<>(SB), NOPTR, $8
   188
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