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runtime: memmove/memclr pointers atomically
Make sure that we're moving or zeroing pointers atomically. Anything that is a multiple of pointer size and at least pointer aligned might have pointers in it. All the code looks ok except for the 1-pointer-sized moves. Fixes #13160 Update #12552 Change-Id: Ib97d9b918fa9f4cc5c56c67ed90255b7fdfb7b45 Reviewed-on: https://go-review.googlesource.com/16668 Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Keith Randall
parent
321a40721b
commit
4b7d5f0b94
10 changed files with 135 additions and 20 deletions
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@ -629,6 +629,9 @@ TEXT runtime·memclr(SB),NOSPLIT,$0-8
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MOVQ BX, CX
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REP
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STOSB
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// Note: we zero only 4 bytes at a time so that the tail is at most
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// 3 bytes. That guarantees that we aren't zeroing pointers with STOSB.
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// See issue 13160.
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RET
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TEXT runtime·getcallerpc(SB),NOSPLIT,$8-12
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@ -21,7 +21,8 @@ tail:
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CMPL BX, $2
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JBE _1or2
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CMPL BX, $4
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JBE _3or4
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JB _3
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JE _4
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CMPL BX, $8
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JBE _5through8
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CMPL BX, $16
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@ -68,9 +69,13 @@ _1or2:
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RET
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_0:
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RET
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_3or4:
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_3:
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MOVW AX, (DI)
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MOVW AX, -2(DI)(BX*1)
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MOVB AX, 2(DI)
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RET
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_4:
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// We need a separate case for 4 to make sure we clear pointers atomically.
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MOVL AX, (DI)
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RET
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_5through8:
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MOVL AX, (DI)
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@ -23,7 +23,8 @@ tail:
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CMPQ BX, $4
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JBE _3or4
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CMPQ BX, $8
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JBE _5through8
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JB _5through7
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JE _8
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CMPQ BX, $16
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JBE _9through16
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PXOR X0, X0
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@ -71,10 +72,14 @@ _3or4:
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MOVW AX, (DI)
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MOVW AX, -2(DI)(BX*1)
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RET
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_5through8:
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_5through7:
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MOVL AX, (DI)
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MOVL AX, -4(DI)(BX*1)
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RET
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_8:
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// We need a separate case for 8 to make sure we clear pointers atomically.
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MOVQ AX, (DI)
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RET
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_9through16:
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MOVQ AX, (DI)
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MOVQ AX, -8(DI)(BX*1)
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@ -16,7 +16,8 @@ tail:
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CMPL BX, $2
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JBE _1or2
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CMPL BX, $4
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JBE _3or4
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JB _3
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JE _4
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CMPL BX, $8
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JBE _5through8
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CMPL BX, $16
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@ -35,9 +36,13 @@ _1or2:
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RET
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_0:
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RET
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_3or4:
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_3:
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MOVW AX, (DI)
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MOVW AX, -2(DI)(BX*1)
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MOVB AX, 2(DI)
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RET
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_4:
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// We need a separate case for 4 to make sure we clear pointers atomically.
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MOVL AX, (DI)
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RET
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_5through8:
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MOVL AX, (DI)
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@ -43,7 +43,8 @@ tail:
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CMPL BX, $2
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JBE move_1or2
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CMPL BX, $4
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JBE move_3or4
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JB move_3
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JE move_4
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CMPL BX, $8
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JBE move_5through8
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CMPL BX, $16
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@ -118,11 +119,16 @@ move_1or2:
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RET
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move_0:
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RET
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move_3or4:
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move_3:
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MOVW (SI), AX
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MOVW -2(SI)(BX*1), CX
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MOVB 2(SI), CX
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MOVW AX, (DI)
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MOVW CX, -2(DI)(BX*1)
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MOVB CX, 2(DI)
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RET
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move_4:
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// We need a separate case for 4 to make sure we write pointers atomically.
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MOVL (SI), AX
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MOVL AX, (DI)
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RET
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move_5through8:
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MOVL (SI), AX
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@ -50,7 +50,8 @@ tail:
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CMPQ BX, $4
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JBE move_3or4
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CMPQ BX, $8
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JBE move_5through8
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JB move_5through7
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JE move_8
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CMPQ BX, $16
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JBE move_9through16
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CMPQ BX, $32
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@ -131,12 +132,17 @@ move_3or4:
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MOVW AX, (DI)
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MOVW CX, -2(DI)(BX*1)
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RET
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move_5through8:
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move_5through7:
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MOVL (SI), AX
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MOVL -4(SI)(BX*1), CX
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MOVL AX, (DI)
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MOVL CX, -4(DI)(BX*1)
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RET
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move_8:
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// We need a separate case for 8 to make sure we write pointers atomically.
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MOVQ (SI), AX
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MOVQ AX, (DI)
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RET
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move_9through16:
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MOVQ (SI), AX
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MOVQ -8(SI)(BX*1), CX
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@ -46,4 +46,7 @@ back:
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REP; MOVSB
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CLD
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// Note: we copy only 4 bytes at a time so that the tail is at most
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// 3 bytes. That guarantees that we aren't copying pointers with MOVSB.
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// See issue 13160.
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RET
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@ -39,7 +39,8 @@ tail:
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CMPL BX, $2
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JBE move_1or2
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CMPL BX, $4
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JBE move_3or4
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JB move_3
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JE move_4
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CMPL BX, $8
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JBE move_5through8
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CMPL BX, $16
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@ -104,11 +105,16 @@ move_1or2:
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RET
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move_0:
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RET
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move_3or4:
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move_3:
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MOVW (SI), AX
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MOVW -2(SI)(BX*1), CX
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MOVB 2(SI), CX
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MOVW AX, (DI)
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MOVW CX, -2(DI)(BX*1)
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MOVB CX, 2(DI)
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RET
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move_4:
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// We need a separate case for 4 to make sure we write pointers atomically.
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MOVL (SI), AX
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MOVL AX, (DI)
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RET
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move_5through8:
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MOVL (SI), AX
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@ -43,7 +43,8 @@ tail:
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CMPQ BX, $4
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JBE move_3or4
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CMPQ BX, $8
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JBE move_5through8
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JB move_5through7
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JE move_8
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CMPQ BX, $16
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JBE move_9through16
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@ -113,12 +114,17 @@ move_3or4:
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MOVW AX, (DI)
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MOVW CX, -2(DI)(BX*1)
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RET
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move_5through8:
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move_5through7:
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MOVL (SI), AX
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MOVL -4(SI)(BX*1), CX
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MOVL AX, (DI)
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MOVL CX, -4(DI)(BX*1)
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RET
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move_8:
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// We need a separate case for 8 to make sure we write pointers atomically.
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MOVQ (SI), AX
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MOVQ AX, (DI)
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RET
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move_9through16:
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MOVQ (SI), AX
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MOVQ -8(SI)(BX*1), CX
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70
test/fixedbugs/issue13160.go
Normal file
70
test/fixedbugs/issue13160.go
Normal file
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@ -0,0 +1,70 @@
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// run
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"fmt"
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"runtime"
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)
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const N = 100000
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func main() {
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// Allocate more Ps than processors. This raises
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// the chance that we get interrupted by the OS
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// in exactly the right (wrong!) place.
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p := runtime.NumCPU()
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runtime.GOMAXPROCS(2 * p)
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// Allocate some pointers.
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ptrs := make([]*int, p)
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for i := 0; i < p; i++ {
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ptrs[i] = new(int)
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}
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// Arena where we read and write pointers like crazy.
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collider := make([]*int, p)
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done := make(chan struct{}, 2*p)
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// Start writers. They alternately write a pointer
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// and nil to a slot in the collider.
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for i := 0; i < p; i++ {
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i := i
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go func() {
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for j := 0; j < N; j++ {
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// Write a pointer using memmove.
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copy(collider[i:i+1], ptrs[i:i+1])
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// Write nil using memclr.
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// (This is a magic loop that gets lowered to memclr.)
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r := collider[i : i+1]
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for k := range r {
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r[k] = nil
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}
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}
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done <- struct{}{}
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}()
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}
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// Start readers. They read pointers from slots
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// and make sure they are valid.
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for i := 0; i < p; i++ {
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i := i
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go func() {
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for j := 0; j < N; j++ {
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var ptr [1]*int
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copy(ptr[:], collider[i:i+1])
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if ptr[0] != nil && ptr[0] != ptrs[i] {
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panic(fmt.Sprintf("bad pointer read %p!", ptr[0]))
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}
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}
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done <- struct{}{}
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}()
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}
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for i := 0; i < 2*p; i++ {
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<-done
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}
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}
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