runtime: fix time.Now on Sierra and older

CL 67332 created the fast no-syscall path for time.Now in High Sierra
but managed to break Sierra and older by forcing them into the slow
syscall path: the version check based on commpage version was wrong.

This CL uses the Darwin version number instead.

The assembly diff is noisy because many variables had to be
renamed, but the only actual change is the version check.

Fixes #23419.

Change-Id: Ie31ef5fb88f66d1517a8693942a7fb6100c213b0
Reviewed-on: https://go-review.googlesource.com/87655
Run-TryBot: Giovanni Bajo <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Austin Clements <[email protected]>

Author: rasky

src/runtime/os_darwin.go

@@ -11,6 +11,8 @@ type mOS struct {
 	waitsema uint32 // semaphore for parking on locks
 }
 
+var darwinVersion int
+
 func bsdthread_create(stk, arg unsafe.Pointer, fn uintptr) int32
 func bsdthread_register() int32
 
@@ -50,16 +52,35 @@ func osinit() {
 	// can look at the environment first.
 
 	ncpu = getncpu()
-
 	physPageSize = getPageSize()
+	darwinVersion = getDarwinVersion()
 }
 
 const (
-	_CTL_HW      = 6
-	_HW_NCPU     = 3
-	_HW_PAGESIZE = 7
+	_CTL_KERN       = 1
+	_CTL_HW         = 6
+	_KERN_OSRELEASE = 2
+	_HW_NCPU        = 3
+	_HW_PAGESIZE    = 7
 )
 
+func getDarwinVersion() int {
+	// Use sysctl to fetch kern.osrelease
+	mib := [2]uint32{_CTL_KERN, _KERN_OSRELEASE}
+	var out [32]byte
+	nout := unsafe.Sizeof(out)
+	ret := sysctl(&mib[0], 2, (*byte)(unsafe.Pointer(&out)), &nout, nil, 0)
+	if ret >= 0 {
+		ver := 0
+		for i := 0; i < int(nout) && out[i] >= '0' && out[i] <= '9'; i++ {
+			ver *= 10
+			ver += int(out[i] - '0')
+		}
+		return ver
+	}
+	return 17 // should not happen: default to a newish version
+}
+
 func getncpu() int32 {
 	// Use sysctl to fetch hw.ncpu.
 	mib := [2]uint32{_CTL_HW, _HW_NCPU}

src/runtime/sys_darwin_amd64.s

@@ -122,36 +122,34 @@ TEXT runtime·madvise(SB), NOSPLIT, $0
 // OS X comm page time offsets
 // https://opensource.apple.com/source/xnu/xnu-4570.1.46/osfmk/i386/cpu_capabilities.h
 
-#define	commpage_version	0x1e
-
-#define	v12_nt_tsc_base	0x50
-#define	v12_nt_scale	0x58
-#define	v12_nt_shift	0x5c
-#define	v12_nt_ns_base	0x60
-#define	v12_nt_generation	0x68
-#define	v12_gtod_generation	0x6c  // obsolete since High Sierra (v13)
-#define	v12_gtod_ns_base	0x70  // obsolete since High Sierra (v13)
-#define	v12_gtod_sec_base	0x78  // obsolete since High Sierra (v13)
-
-#define	v13_gtod_ns_base	0xd0
-#define	v13_gtod_sec_ofs	0xd8
-#define	v13_gtod_frac_ofs	0xe0
-#define	v13_gtod_scale		0xe8
-#define	v13_gtod_tkspersec	0xf0
+#define	nt_tsc_base	0x50
+#define	nt_scale	0x58
+#define	nt_shift	0x5c
+#define	nt_ns_base	0x60
+#define	nt_generation	0x68
+#define	gtod_generation	0x6c  // obsolete since Darwin v17 (High Sierra)
+#define	gtod_ns_base	0x70  // obsolete since Darwin v17 (High Sierra)
+#define	gtod_sec_base	0x78  // obsolete since Darwin v17 (High Sierra)
+
+#define	v17_gtod_ns_base	0xd0
+#define	v17_gtod_sec_ofs	0xd8
+#define	v17_gtod_frac_ofs	0xe0
+#define	v17_gtod_scale		0xe8
+#define	v17_gtod_tkspersec	0xf0
 
 TEXT runtime·nanotime(SB),NOSPLIT,$0-8
 	MOVQ	$0x7fffffe00000, BP	/* comm page base */
 	// Loop trying to take a consistent snapshot
 	// of the time parameters.
 timeloop:
-	MOVL	v12_nt_generation(BP), R9
+	MOVL	nt_generation(BP), R9
 	TESTL	R9, R9
 	JZ	timeloop
 	RDTSC
-	MOVQ	v12_nt_tsc_base(BP), R10
-	MOVL	v12_nt_scale(BP), R11
-	MOVQ	v12_nt_ns_base(BP), R12
-	CMPL	v12_nt_generation(BP), R9
+	MOVQ	nt_tsc_base(BP), R10
+	MOVL	nt_scale(BP), R11
+	MOVQ	nt_ns_base(BP), R12
+	CMPL	nt_generation(BP), R9
 	JNE	timeloop
 
 	// Gathered all the data we need. Compute monotonic time:
@@ -173,32 +171,32 @@ TEXT time·now(SB), NOSPLIT, $32-24
 	// are used in the systime fallback, as the timeval address
 	// filled in by the system call.
 	MOVQ	$0x7fffffe00000, BP	/* comm page base */
-	CMPW	commpage_version(BP), $13
-	JB		v12 /* sierra and older */
+	CMPQ	runtime·darwinVersion(SB), $17
+	JB		legacy /* sierra and older */
 
-	// This is the new code, for macOS High Sierra (v13) and newer.
-v13:
+	// This is the new code, for macOS High Sierra (Darwin v17) and newer.
+v17:
 	// Loop trying to take a consistent snapshot
 	// of the time parameters.
-timeloop13:
-	MOVQ 	v13_gtod_ns_base(BP), R12
+timeloop17:
+	MOVQ 	v17_gtod_ns_base(BP), R12
 
-	MOVL	v12_nt_generation(BP), CX
+	MOVL	nt_generation(BP), CX
 	TESTL	CX, CX
-	JZ		timeloop13
+	JZ		timeloop17
 	RDTSC
-	MOVQ	v12_nt_tsc_base(BP), SI
-	MOVL	v12_nt_scale(BP), DI
-	MOVQ	v12_nt_ns_base(BP), BX
-	CMPL	v12_nt_generation(BP), CX
-	JNE		timeloop13
-
-	MOVQ 	v13_gtod_sec_ofs(BP), R8
-	MOVQ 	v13_gtod_frac_ofs(BP), R9
-	MOVQ 	v13_gtod_scale(BP), R10
-	MOVQ 	v13_gtod_tkspersec(BP), R11
-	CMPQ 	v13_gtod_ns_base(BP), R12
-	JNE 	timeloop13
+	MOVQ	nt_tsc_base(BP), SI
+	MOVL	nt_scale(BP), DI
+	MOVQ	nt_ns_base(BP), BX
+	CMPL	nt_generation(BP), CX
+	JNE		timeloop17
+
+	MOVQ 	v17_gtod_sec_ofs(BP), R8
+	MOVQ 	v17_gtod_frac_ofs(BP), R9
+	MOVQ 	v17_gtod_scale(BP), R10
+	MOVQ 	v17_gtod_tkspersec(BP), R11
+	CMPQ 	v17_gtod_ns_base(BP), R12
+	JNE 	timeloop17
 
 	// Compute monotonic time
 	//	mono = ((tsc - nt_tsc_base) * nt_scale) >> 32 + nt_ns_base
@@ -240,24 +238,24 @@ timeloop13:
 	MOVQ	DX, nsec+8(FP)
 	RET
 
-	// This is the legacy code needed for macOS Sierra (v12) and older.
-v12:
+	// This is the legacy code needed for macOS Sierra (Darwin v16) and older.
+legacy:
 	// Loop trying to take a consistent snapshot
 	// of the time parameters.
 timeloop:
-	MOVL	v12_gtod_generation(BP), R8
-	MOVL	v12_nt_generation(BP), R9
+	MOVL	gtod_generation(BP), R8
+	MOVL	nt_generation(BP), R9
 	TESTL	R9, R9
 	JZ	timeloop
 	RDTSC
-	MOVQ	v12_nt_tsc_base(BP), R10
-	MOVL	v12_nt_scale(BP), R11
-	MOVQ	v12_nt_ns_base(BP), R12
-	CMPL	v12_nt_generation(BP), R9
+	MOVQ	nt_tsc_base(BP), R10
+	MOVL	nt_scale(BP), R11
+	MOVQ	nt_ns_base(BP), R12
+	CMPL	nt_generation(BP), R9
 	JNE	timeloop
-	MOVQ	v12_gtod_ns_base(BP), R13
-	MOVQ	v12_gtod_sec_base(BP), R14
-	CMPL	v12_gtod_generation(BP), R8
+	MOVQ	gtod_ns_base(BP), R13
+	MOVQ	gtod_sec_base(BP), R14
+	CMPL	gtod_generation(BP), R8
 	JNE	timeloop
 
 	// Gathered all the data we need. Compute: