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sync/atomic: fix 64-bit atomic cas for Linux/ARM

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This is a follow-up to CL 5978051.
    Use kernel cas64 helper if we can, fallback to LDREXD/STREXD if
    we are on ARMv6 or higher, and to lock-emulated cas64 if on ARMv5.
    A future CL will fix {Add,Load,Store}{Int,Uint}64 and issue 3331.

R=bradfitz, rsc
CC=golang-dev
https://golang.org/cl/6034048
This commit is contained in:
Shenghou Ma 2012-05-05 02:02:36 +08:00
parent a642ca4930
commit 4d724f4c5b
1 changed files with 55 additions and 6 deletions
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61
src/pkg/sync/atomic/asm_linux_arm.s
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@ -72,14 +72,63 @@ addloop1:
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 cas64<>(SB),7,$0
MOVW $0xffff0f60, PC // __kuser_cmpxchg64: Linux-3.1 and above
TEXT kernelCAS64<>(SB),7,$0
// int (*__kuser_cmpxchg64_t)(const int64_t *oldval, const int64_t *newval, volatile int64_t *ptr);
MOVW valptr+0(FP), R2 // ptr
MOVW $4(FP), R0 // oldval
MOVW $12(FP), R1 // newval
BL cas64<>(SB)
MOVW.CS $1, R0 // C is set if the kernel has changed *ptr
MOVW.CC $0, R0
MOVW R0, 20(FP)
RET
TEXT generalCAS64<>(SB),7,$20
// bool runtime·cas64(uint64 volatile *addr, uint64 *old, uint64 new)
MOVW valptr+0(FP), R0
MOVW R0, 4(R13)
MOVW $4(FP), R1 // oldval
MOVW R1, 8(R13)
MOVW newlo+12(FP), R2
MOVW R2, 12(R13)
MOVW newhi+16(FP), R3
MOVW R3, 16(R13)
BL runtime·cas64(SB)
MOVW R0, 20(FP)
RET
GLOBL armCAS64(SB), $4
TEXT setupAndCallCAS64<>(SB),7,$-4
MOVW $0xffff0ffc, R0 // __kuser_helper_version
MOVW (R0), R0
// __kuser_cmpxchg64 only present if helper version >= 5
CMP $5, R0
MOVW.CS $kernelCAS64<>(SB), R1
MOVW.CS R1, armCAS64(SB)
MOVW.CS R1, PC
MOVB runtime·armArch(SB), R0
// LDREXD, STREXD only present on ARMv6K or higher
CMP $6, R0 // TODO(minux): how to differentiate ARMv6 with ARMv6K?
MOVW.CS $·armCompareAndSwapUint64(SB), R1
MOVW.CS R1, armCAS64(SB)
MOVW.CS R1, PC
// we are out of luck, can only use runtime's emulated 64-bit cas
MOVW $generalCAS64<>(SB), R1
MOVW R1, armCAS64(SB)
MOVW R1, PC
TEXT ·CompareAndSwapInt64(SB),7,$-4
MOVW armCAS64(SB), R0
CMP $0, R0
MOVW.NE R0, PC
B setupAndCallCAS64<>(SB)
TEXT ·CompareAndSwapUint64(SB),7,$0
B ·armCompareAndSwapUint64(SB)
B ·CompareAndSwapInt64(SB)
TEXT ·AddInt64(SB),7,$0
B ·armAddUint64(SB)