runtime: use timer_settime64 on 32-bit 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 64-bit syscall for timer_settime by default.
Add a fallback to use the 32-bit syscall when the
64-bit version returns _ENOSYS.

Fixes #75133

Change-Id: Iccb8831b67f665067ee526e93c3ff2f4f5392edf
GitHub-Last-Rev: 6c3d62d60e
GitHub-Pull-Request: golang/go#75957
Reviewed-on: https://go-review.googlesource.com/c/go/+/712642
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>

src/runtime/defs_linux_386.go

@@ -237,10 +237,14 @@ type ucontext struct {
 	uc_sigmask  uint32
 }
 
-type itimerspec struct {
+type itimerspec32 struct {
 	it_interval timespec32
 	it_value    timespec32
 }
+type itimerspec struct {
+	it_interval timespec
+	it_value    timespec
+}
 
 type itimerval struct {
 	it_interval timeval

src/runtime/defs_linux_arm.go

@@ -169,11 +169,16 @@ func (tv *timeval) set_usec(x int32) {
 	tv.tv_usec = x
 }
 
-type itimerspec struct {
+type itimerspec32 struct {
 	it_interval timespec32
 	it_value    timespec32
 }
 
+type itimerspec struct {
+	it_interval timespec
+	it_value    timespec
+}
+
 type itimerval struct {
 	it_interval timeval
 	it_value    timeval

src/runtime/defs_linux_mipsx.go

@@ -152,11 +152,16 @@ type siginfo struct {
 	_ [_si_max_size - unsafe.Sizeof(siginfoFields{})]byte
 }
 
-type itimerspec struct {
+type itimerspec32 struct {
 	it_interval timespec32
 	it_value    timespec32
 }
 
+type itimerspec struct {
+	it_interval timespec
+	it_value    timespec
+}
+
 type itimerval struct {
 	it_interval timeval
 	it_value    timeval

src/runtime/os_linux.go

@@ -435,9 +435,6 @@ func setitimer(mode int32, new, old *itimerval)
 //go:noescape
 func timer_create(clockid int32, sevp *sigevent, timerid *int32) int32
 
-//go:noescape
-func timer_settime(timerid int32, flags int32, new, old *itimerspec) int32
-
 //go:noescape
 func timer_delete(timerid int32) int32
 

src/runtime/os_linux_settime32.go

@@ -0,0 +1,47 @@
+// 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)
+
+package runtime
+
+import "internal/runtime/atomic"
+
+var timer32bitOnly atomic.Bool
+
+//go:noescape
+func timer_settime32(timerid int32, flags int32, new, old *itimerspec32) int32
+
+//go:noescape
+func timer_settime64(timerid int32, flags int32, new, old *itimerspec) int32
+
+//go:nosplit
+func timer_settime(timerid int32, flags int32, new, old *itimerspec) int32 {
+	if !timer32bitOnly.Load() {
+		ret := timer_settime64(timerid, flags, new, old)
+		// timer_settime64 is only supported on Linux 5.0+
+		if ret != -_ENOSYS {
+			return ret
+		}
+		timer32bitOnly.Store(true)
+	}
+
+	var newts,oldts itimerspec32
+	var new32,old32 *itimerspec32
+
+	if new != nil {
+		newts.it_interval.setNsec(new.it_interval.tv_sec*1e9 + new.it_interval.tv_nsec)
+		newts.it_value.setNsec(new.it_value.tv_sec*1e9 + new.it_value.tv_nsec)
+		new32 = &newts
+	}
+
+	if old != nil {
+		oldts.it_interval.setNsec(old.it_interval.tv_sec*1e9 + old.it_interval.tv_nsec)
+		oldts.it_value.setNsec(old.it_value.tv_sec*1e9 + old.it_value.tv_nsec)
+		old32 = &oldts
+	}
+
+	// Fall back to 32-bit timer
+	return timer_settime32(timerid, flags, new32, old32)
+}

src/runtime/os_linux_settime64.go

@@ -0,0 +1,10 @@
+// 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)
+
+package runtime
+
+//go:noescape
+func timer_settime(timerid int32, flags int32, new, old *itimerspec) int32

src/runtime/sys_linux_386.s

@@ -54,6 +54,7 @@
 #define SYS_exit_group		252
 #define SYS_timer_create	259
 #define SYS_timer_settime	260
+#define SYS_timer_settime64	409
 #define SYS_timer_delete	263
 #define SYS_clock_gettime	265
 #define SYS_tgkill		270
@@ -209,7 +210,8 @@ TEXT runtime·timer_create(SB),NOSPLIT,$0-16
 	MOVL	AX, ret+12(FP)
 	RET
 
-TEXT runtime·timer_settime(SB),NOSPLIT,$0-20
+// Linux: kernel/time/posix-timer.c, requiring COMPAT_32BIT_TIME
+TEXT runtime·timer_settime32(SB),NOSPLIT,$0-20
 	MOVL	$SYS_timer_settime, AX
 	MOVL	timerid+0(FP), BX
 	MOVL	flags+4(FP), CX
@@ -219,6 +221,16 @@ TEXT runtime·timer_settime(SB),NOSPLIT,$0-20
 	MOVL	AX, ret+16(FP)
 	RET
 
+TEXT runtime·timer_settime64(SB),NOSPLIT,$0-20
+	MOVL	$SYS_timer_settime64, AX
+	MOVL	timerid+0(FP), BX
+	MOVL	flags+4(FP), CX
+	MOVL	new+8(FP), DX
+	MOVL	old+12(FP), SI
+	INVOKE_SYSCALL
+	MOVL	AX, ret+16(FP)
+	RET
+
 TEXT runtime·timer_delete(SB),NOSPLIT,$0-8
 	MOVL	$SYS_timer_delete, AX
 	MOVL	timerid+0(FP), BX

src/runtime/sys_linux_arm.s

@@ -44,6 +44,7 @@
 #define SYS_clock_gettime (SYS_BASE + 263)
 #define SYS_timer_create (SYS_BASE + 257)
 #define SYS_timer_settime (SYS_BASE + 258)
+#define SYS_timer_settime64 (SYS_BASE + 409)
 #define SYS_timer_delete (SYS_BASE + 261)
 #define SYS_pipe2 (SYS_BASE + 359)
 #define SYS_access (SYS_BASE + 33)
@@ -231,8 +232,8 @@ TEXT runtime·timer_create(SB),NOSPLIT,$0-16
 	SWI	$0
 	MOVW	R0, ret+12(FP)
 	RET
-
+// Linux: kernel/time/posix-timer.c, requiring COMPAT_32BIT_TIME.
-TEXT runtime·timer_settime(SB),NOSPLIT,$0-20
+TEXT runtime·timer_settime32(SB),NOSPLIT,$0-20
 	MOVW	timerid+0(FP), R0
 	MOVW	flags+4(FP), R1
 	MOVW	new+8(FP), R2
@@ -242,6 +243,16 @@ TEXT runtime·timer_settime(SB),NOSPLIT,$0-20
 	MOVW	R0, ret+16(FP)
 	RET
 
+TEXT runtime·timer_settime64(SB),NOSPLIT,$0-20
+	MOVW	timerid+0(FP), R0
+	MOVW	flags+4(FP), R1
+	MOVW	new+8(FP), R2
+	MOVW	old+12(FP), R3
+	MOVW	$SYS_timer_settime64, R7
+	SWI	$0
+	MOVW	R0, ret+16(FP)
+	RET
+
 TEXT runtime·timer_delete(SB),NOSPLIT,$0-8
 	MOVW	timerid+0(FP), R0
 	MOVW	$SYS_timer_delete, R7

src/runtime/sys_linux_mipsx.s

@@ -39,6 +39,7 @@
 #define SYS_exit_group		4246
 #define SYS_timer_create	4257
 #define SYS_timer_settime	4258
+#define SYS_timer_settime64	4409
 #define SYS_timer_delete	4261
 #define SYS_clock_gettime	4263
 #define SYS_tgkill		4266
@@ -197,7 +198,8 @@ TEXT runtime·timer_create(SB),NOSPLIT,$0-16
 	MOVW	R2, ret+12(FP)
 	RET
 
-TEXT runtime·timer_settime(SB),NOSPLIT,$0-20
+// Linux: kernel/time/posix-timer.c, requiring COMPAT_32BIT_TIME
+TEXT runtime·timer_settime32(SB),NOSPLIT,$0-20
 	MOVW	timerid+0(FP), R4
 	MOVW	flags+4(FP), R5
 	MOVW	new+8(FP), R6
@@ -207,6 +209,16 @@ TEXT runtime·timer_settime(SB),NOSPLIT,$0-20
 	MOVW	R2, ret+16(FP)
 	RET
 
+TEXT runtime·timer_settime64(SB),NOSPLIT,$0-20
+	MOVW	timerid+0(FP), R4
+	MOVW	flags+4(FP), R5
+	MOVW	new+8(FP), R6
+	MOVW	old+12(FP), R7
+	MOVW	$SYS_timer_settime64, R2
+	SYSCALL
+	MOVW	R2, ret+16(FP)
+	RET
+
 TEXT runtime·timer_delete(SB),NOSPLIT,$0-8
 	MOVW	timerid+0(FP), R4
 	MOVW	$SYS_timer_delete, R2