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runtime: use mach_absolute_time for runtime.nanotime

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The existing darwin/amd64 implementation of runtime.nanotime returns the
wallclock time, which results in timers not functioning properly when
system time runs backwards. By implementing the algorithm used by the
darwin syscall mach_absolute_time, timers will function as expected.

The algorithm is described at
https://opensource.apple.com/source/xnu/xnu-3248.60.10/libsyscall/wrappers/mach_absolute_time.s

Fixes #17610

Change-Id: I9c8d35240d48249a6837dca1111b1406e2686f67
Reviewed-on: https://go-review.googlesource.com/35292
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Lars Wiegman 2017-01-17 11:38:18 +01:00 committed by Russ Cox
parent 8958d8ce37
commit e546b295b8
1 changed files with 22 additions and 1 deletions
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23
src/runtime/sys_darwin_amd64.s
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@ -117,6 +117,27 @@ TEXT runtime·madvise(SB), NOSPLIT, $0
#define gtod_ns_base 0x70
#define gtod_sec_base 0x78
TEXT monotonictime<>(SB), NOSPLIT, $32
MOVQ $0x7fffffe00000, SI // comm page base
timeloop:
MOVL nt_generation(SI), R8
TESTL R8, R8
JZ timeloop
RDTSC
SHLQ $32, DX
ORQ DX, AX
MOVL nt_shift(SI), CX
SUBQ nt_tsc_base(SI), AX
SHLQ CX, AX
MOVL nt_scale(SI), CX
MULQ CX
SHRQ $32, AX:DX
ADDQ nt_ns_base(SI), AX
CMPL nt_generation(SI), R8
JNE timeloop
RET
TEXT nanotime<>(SB), NOSPLIT, $32
MOVQ $0x7fffffe00000, BP /* comm page base */
// Loop trying to take a consistent snapshot
@ -173,7 +194,7 @@ inreg:
RET
TEXT runtime·nanotime(SB),NOSPLIT,$0-8
CALL nanotime<>(SB)
CALL monotonictime<>(SB)
MOVQ AX, ret+0(FP)
RET