runtime: use futexes with 64-bit time on Linux

Linux introduced new syscalls to fix the year 2038 issue.
To still be able to use the old ones, the Kconfig option
COMPAT_32BIT_TIME would be necessary.

Use the new syscall with 64-bit values for futexwakeup by default.
Define _ENOSYS for detecting if it's not available.
Add a fallback to use the older syscall in case the new one is
not available, since Go runs on Linux from 2.6.32 on, per
https://go.dev/wiki/MinimumRequirements.

Fixes #75133

src/runtime/defs2_linux.go

@@ -48,6 +48,7 @@ const (
 	EINTR  = C.EINTR
 	EAGAIN = C.EAGAIN
 	ENOMEM = C.ENOMEM
+	ENOSYS = C.ENOSYS
 
 	PROT_NONE  = C.PROT_NONE
 	PROT_READ  = C.PROT_READ

src/runtime/defs_linux.go

@@ -37,6 +37,7 @@ const (
 	EINTR  = C.EINTR
 	EAGAIN = C.EAGAIN
 	ENOMEM = C.ENOMEM
+	ENOSYS = C.ENOSYS
 
 	PROT_NONE  = C.PROT_NONE
 	PROT_READ  = C.PROT_READ

src/runtime/defs_linux_386.go

@@ -9,6 +9,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1
@@ -136,16 +137,30 @@ type fpstate struct {
 	anon0     [48]byte
 }
 
-type timespec struct {
+// The timespec structs and types are defined in Linux in
+// include/uapi/linux/time_types.h and include/uapi/asm-generic/posix_types.h.
+type timespec32 struct {
 	tv_sec  int32
 	tv_nsec int32
 }
 
 //go:nosplit
-func (ts *timespec) setNsec(ns int64) {
+func (ts *timespec32) setNsec(ns int64) {
 	ts.tv_sec = timediv(ns, 1e9, &ts.tv_nsec)
 }
 
+type timespec struct {
+	tv_sec  int64
+	tv_nsec int64
+}
+
+//go:nosplit
+func (ts *timespec) setNsec(ns int64) {
+	var newNS int32
+	ts.tv_sec = int64(timediv(ns, 1e9, &newNS))
+	ts.tv_nsec = int64(newNS)
+}
+
 type timeval struct {
 	tv_sec  int32
 	tv_usec int32
@@ -223,8 +238,8 @@ type ucontext struct {
 }
 
 type itimerspec struct {
-	it_interval timespec
+	it_interval timespec32
-	it_value    timespec
+	it_value    timespec32
 }
 
 type itimerval struct {

src/runtime/defs_linux_amd64.go

@@ -9,6 +9,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/defs_linux_arm.go

@@ -11,6 +11,7 @@ const (
 	_EINTR  = 0x4
 	_ENOMEM = 0xc
 	_EAGAIN = 0xb
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0
 	_PROT_READ  = 0x1
@@ -95,16 +96,30 @@ const (
 	_SOCK_DGRAM = 0x2
 )
 
-type timespec struct {
+// The timespec structs and types are defined in Linux in
+// include/uapi/linux/time_types.h and include/uapi/asm-generic/posix_types.h.
+type timespec32 struct {
 	tv_sec  int32
 	tv_nsec int32
 }
 
 //go:nosplit
-func (ts *timespec) setNsec(ns int64) {
+func (ts *timespec32) setNsec(ns int64) {
 	ts.tv_sec = timediv(ns, 1e9, &ts.tv_nsec)
 }
 
+type timespec struct {
+	tv_sec  int64
+	tv_nsec int64
+}
+
+//go:nosplit
+func (ts *timespec) setNsec(ns int64) {
+	var newNS int32
+	ts.tv_sec = int64(timediv(ns, 1e9, &newNS))
+	ts.tv_nsec = int64(newNS)
+}
+
 type stackt struct {
 	ss_sp    *byte
 	ss_flags int32
@@ -155,8 +170,8 @@ func (tv *timeval) set_usec(x int32) {
 }
 
 type itimerspec struct {
-	it_interval timespec
+	it_interval timespec32
-	it_value    timespec
+	it_value    timespec32
 }
 
 type itimerval struct {

src/runtime/defs_linux_arm64.go

@@ -9,6 +9,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/defs_linux_loong64.go

@@ -10,6 +10,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/defs_linux_mips64x.go

@@ -12,6 +12,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/defs_linux_mipsx.go

@@ -12,6 +12,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1
@@ -93,16 +94,30 @@ const (
 	_SIGEV_THREAD_ID = 0x4
 )
 
-type timespec struct {
+// The timespec structs and types are defined in Linux in
+// include/uapi/linux/time_types.h and include/uapi/asm-generic/posix_types.h.
+type timespec32 struct {
 	tv_sec  int32
 	tv_nsec int32
 }
 
 //go:nosplit
-func (ts *timespec) setNsec(ns int64) {
+func (ts *timespec32) setNsec(ns int64) {
 	ts.tv_sec = timediv(ns, 1e9, &ts.tv_nsec)
 }
 
+type timespec struct {
+	tv_sec  int64
+	tv_nsec int64
+}
+
+//go:nosplit
+func (ts *timespec) setNsec(ns int64) {
+	var newNS int32
+	ts.tv_sec = int64(timediv(ns, 1e9, &newNS))
+	ts.tv_nsec = int64(newNS)
+}
+
 type timeval struct {
 	tv_sec  int32
 	tv_usec int32
@@ -138,8 +153,8 @@ type siginfo struct {
 }
 
 type itimerspec struct {
-	it_interval timespec
+	it_interval timespec32
-	it_value    timespec
+	it_value    timespec32
 }
 
 type itimerval struct {

src/runtime/defs_linux_ppc64.go

@@ -9,6 +9,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/defs_linux_ppc64le.go

@@ -9,6 +9,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/defs_linux_riscv64.go

@@ -10,6 +10,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/defs_linux_s390x.go

@@ -10,6 +10,7 @@ const (
 	_EINTR  = 0x4
 	_EAGAIN = 0xb
 	_ENOMEM = 0xc
+	_ENOSYS = 0x26
 
 	_PROT_NONE  = 0x0
 	_PROT_READ  = 0x1

src/runtime/os_linux.go

@@ -40,9 +40,6 @@ type mOS struct {
 	waitsema uint32 // semaphore for parking on locks
 }
 
-//go:noescape
-func futex(addr unsafe.Pointer, op int32, val uint32, ts, addr2 unsafe.Pointer, val3 uint32) int32
-
 // Linux futex.
 //
 //	futexsleep(uint32 *addr, uint32 val)
@@ -79,7 +76,7 @@ func futexsleep(addr *uint32, val uint32, ns int64) {
 
 	var ts timespec
 	ts.setNsec(ns)
-	futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, unsafe.Pointer(&ts), nil, 0)
+	futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, &ts, nil, 0)
 }
 
 // If any procs are sleeping on addr, wake up at most cnt.

src/runtime/os_linux_futex32.go

@@ -0,0 +1,40 @@
+// Copyright 2025 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.
+
+//go:build linux && (386 || arm || mips || mipsle || ppc)
+
+package runtime
+
+import (
+	"internal/runtime/atomic"
+	"unsafe"
+)
+
+//go:noescape
+func futex_time32(addr unsafe.Pointer, op int32, val uint32, ts *timespec32, addr2 unsafe.Pointer, val3 uint32) int32
+
+//go:noescape
+func futex_time64(addr unsafe.Pointer, op int32, val uint32, ts *timespec, addr2 unsafe.Pointer, val3 uint32) int32
+
+var is32bitOnly atomic.Bool
+
+//go:nosplit
+func futex(addr unsafe.Pointer, op int32, val uint32, ts *timespec, addr2 unsafe.Pointer, val3 uint32) int32 {
+	if !is32bitOnly.Load() {
+		ret := futex_time64(addr, op, val, ts, addr2, val3)
+		// futex_time64 is only supported on Linux 5.0+
+		if ret != -_ENOSYS {
+			return ret
+		}
+		is32bitOnly.Store(true)
+	}
+	// Downgrade ts.
+	var ts32 timespec32
+	var pts32 *timespec32
+	if ts != nil {
+		ts32.setNsec(ts.tv_sec*1e9 + ts.tv_nsec)
+		pts32 = &ts32
+	}
+	return futex_time32(addr, op, val, pts32, addr2, val3)
+}

src/runtime/os_linux_futex64.go

@@ -0,0 +1,14 @@
+// Copyright 2025 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.
+
+//go:build linux && !(386 || arm || mips || mipsle || ppc || s390)
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+//go:noescape
+func futex(addr unsafe.Pointer, op int32, val uint32, ts *timespec, addr2 unsafe.Pointer, val3 uint32) int32

src/runtime/sys_linux_386.s

@@ -48,6 +48,7 @@
 #define SYS_madvise		219
 #define SYS_gettid		224
 #define SYS_futex		240
+#define SYS_futex_time64	422
 #define SYS_sched_getaffinity	242
 #define SYS_set_thread_area	243
 #define SYS_exit_group		252
@@ -532,10 +533,26 @@ TEXT runtime·madvise(SB),NOSPLIT,$0
 	MOVL	AX, ret+12(FP)
 	RET
 
+// Linux: kernel/futex/syscalls.c, requiring COMPAT_32BIT_TIME
+// int32 futex(int32 *uaddr, int32 op, int32 val,
+//	struct old_timespec32 *timeout, int32 *uaddr2, int32 val2);
+TEXT runtime·futex_time32(SB),NOSPLIT,$0
+	MOVL	$SYS_futex, AX
+	MOVL	addr+0(FP), BX
+	MOVL	op+4(FP), CX
+	MOVL	val+8(FP), DX
+	MOVL	ts+12(FP), SI
+	MOVL	addr2+16(FP), DI
+	MOVL	val3+20(FP), BP
+	INVOKE_SYSCALL
+	MOVL	AX, ret+24(FP)
+	RET
+
+// Linux: kernel/futex/syscalls.c
 // int32 futex(int32 *uaddr, int32 op, int32 val,
 //	struct timespec *timeout, int32 *uaddr2, int32 val2);
-TEXT runtime·futex(SB),NOSPLIT,$0
+TEXT runtime·futex_time64(SB),NOSPLIT,$0
-	MOVL	$SYS_futex, AX
+	MOVL	$SYS_futex_time64, AX
 	MOVL	addr+0(FP), BX
 	MOVL	op+4(FP), CX
 	MOVL	val+8(FP), DX

src/runtime/sys_linux_arm.s

@@ -30,6 +30,7 @@
 #define SYS_sigaltstack (SYS_BASE + 186)
 #define SYS_mmap2 (SYS_BASE + 192)
 #define SYS_futex (SYS_BASE + 240)
+#define SYS_futex_time64 (SYS_BASE + 422)
 #define SYS_exit_group (SYS_BASE + 248)
 #define SYS_munmap (SYS_BASE + 91)
 #define SYS_madvise (SYS_BASE + 220)
@@ -403,9 +404,10 @@ finish:
 
 	RET
 
+// Linux: kernel/futex/syscalls.c, requiring COMPAT_32BIT_TIME
 // int32 futex(int32 *uaddr, int32 op, int32 val,
-//	struct timespec *timeout, int32 *uaddr2, int32 val2);
+//	struct old_timespec32 *timeout, int32 *uaddr2, int32 val2);
-TEXT runtime·futex(SB),NOSPLIT,$0
+TEXT runtime·futex_time32(SB),NOSPLIT,$0
 	MOVW    addr+0(FP), R0
 	MOVW    op+4(FP), R1
 	MOVW    val+8(FP), R2
@@ -417,6 +419,21 @@ TEXT runtime·futex(SB),NOSPLIT,$0
 	MOVW	R0, ret+24(FP)
 	RET
 
+// Linux: kernel/futex/syscalls.c
+// int32 futex(int32 *uaddr, int32 op, int32 val,
+//	struct timespec *timeout, int32 *uaddr2, int32 val2);
+TEXT runtime·futex_time64(SB),NOSPLIT,$0
+	MOVW    addr+0(FP), R0
+	MOVW    op+4(FP), R1
+	MOVW    val+8(FP), R2
+	MOVW    ts+12(FP), R3
+	MOVW    addr2+16(FP), R4
+	MOVW    val3+20(FP), R5
+	MOVW	$SYS_futex_time64, R7
+	SWI	$0
+	MOVW	R0, ret+24(FP)
+	RET
+
 // int32 clone(int32 flags, void *stack, M *mp, G *gp, void (*fn)(void));
 TEXT runtime·clone(SB),NOSPLIT,$0
 	MOVW	flags+0(FP), R0

src/runtime/sys_linux_mipsx.s

@@ -34,6 +34,7 @@
 #define SYS_mincore		4217
 #define SYS_gettid		4222
 #define SYS_futex		4238
+#define SYS_futex_time64	4422
 #define SYS_sched_getaffinity	4240
 #define SYS_exit_group		4246
 #define SYS_timer_create	4257
@@ -362,8 +363,10 @@ TEXT runtime·madvise(SB),NOSPLIT,$0-16
 	MOVW	R2, ret+12(FP)
 	RET
 
-// int32 futex(int32 *uaddr, int32 op, int32 val, struct timespec *timeout, int32 *uaddr2, int32 val2);
+// Linux: kernel/futex/syscalls.c, requiring COMPAT_32BIT_TIME
-TEXT runtime·futex(SB),NOSPLIT,$20-28
+// int32 futex(int32 *uaddr, int32 op, int32 val,
+//	struct old_timespec32 *timeout, int32 *uaddr2, int32 val2);
+TEXT runtime·futex_time32(SB),NOSPLIT,$20-28
 	MOVW	addr+0(FP), R4
 	MOVW	op+4(FP), R5
 	MOVW	val+8(FP), R6
@@ -382,6 +385,27 @@ TEXT runtime·futex(SB),NOSPLIT,$20-28
 	MOVW	R2, ret+24(FP)
 	RET
 
+// Linux: kernel/futex/syscalls.c
+// int32 futex(int32 *uaddr, int32 op, int32 val,
+//	struct timespec *timeout, int32 *uaddr2, int32 val2);
+TEXT runtime·futex_time64(SB),NOSPLIT,$20-28
+	MOVW	addr+0(FP), R4
+	MOVW	op+4(FP), R5
+	MOVW	val+8(FP), R6
+	MOVW	ts+12(FP), R7
+
+	MOVW	addr2+16(FP), R8
+	MOVW	val3+20(FP), R9
+
+	MOVW	R8, 16(R29)
+	MOVW	R9, 20(R29)
+
+	MOVW	$SYS_futex_time64, R2
+	SYSCALL
+	BEQ	R7, 2(PC)
+	SUBU	R2, R0, R2	// caller expects negative errno
+	MOVW	R2, ret+24(FP)
+	RET
 
 // int32 clone(int32 flags, void *stk, M *mp, G *gp, void (*fn)(void));
 TEXT runtime·clone(SB),NOSPLIT|NOFRAME,$0-24