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// Copyright 2011 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.
// Linux/ARM atomic operations.
// Because there is so much variation in ARM devices,
// the Linux kernel provides an appropriate compare-and-swap
// implementation at address 0xffff0fc0. Caller sets:
// R0 = old value
// R1 = new value
// R2 = valptr
// LR = return address
// The function returns with CS true if the swap happened.
// http://lxr.linux.no/linux+v2.6.37.2/arch/arm/kernel/entry-armv.S#L850
// On older kernels (before 2.6.24) the function can incorrectly
// report a conflict, so we have to double-check the compare ourselves
// and retry if necessary.
//
// http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b49c0f24cf6744a3f4fd09289fe7cade349dead5
//
TEXT cas<>(SB),7,$0
MOVW $0xffff0fc0, PC
TEXT ·CompareAndSwapInt32(SB),7,$0
B ·CompareAndSwapUint32(SB)
// Implement using kernel cas for portability.
TEXT ·CompareAndSwapUint32(SB),7,$0
MOVW valptr+0(FP), R2
MOVW old+4(FP), R0
casagain:
MOVW new+8(FP), R1
BL cas<>(SB)
BCC cascheck
MOVW $1, R0
casret:
MOVW R0, ret+12(FP)
RET
cascheck:
// Kernel lies; double-check.
MOVW valptr+0(FP), R2
MOVW old+4(FP), R0
MOVW 0(R2), R3
CMP R0, R3
BEQ casagain
MOVW $0, R0
B casret
TEXT ·CompareAndSwapUintptr(SB),7,$0
B ·CompareAndSwapUint32(SB)
TEXT ·AddInt32(SB),7,$0
B ·AddUint32(SB)
// Implement using kernel cas for portability.
TEXT ·AddUint32(SB),7,$0
MOVW valptr+0(FP), R2
MOVW delta+4(FP), R4
addloop1:
MOVW 0(R2), R0
MOVW R0, R1
ADD R4, R1
BL cas<>(SB)
BCC addloop1
MOVW R1, ret+8(FP)
RET
TEXT ·AddUintptr(SB),7,$0
B ·AddUint32(SB)
// The kernel provides no 64-bit compare-and-swap,
// so use native ARM instructions, which will only work on
// ARM 11 and later devices.
TEXT ·CompareAndSwapInt64(SB),7,$0
B ·armCompareAndSwapUint64(SB)
TEXT ·CompareAndSwapUint64(SB),7,$0
B ·armCompareAndSwapUint64(SB)
TEXT ·AddInt64(SB),7,$0
B ·armAddUint64(SB)
TEXT ·AddUint64(SB),7,$0
B ·armAddUint64(SB)
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