// MADV_FREE was added in Linux 4.5. Fall back on MADV_DONTNEED if it's
		// not supported.
		if madvise(v, n, _MADV_DONTNEED) == 0 {
			break
		}
		atomic.Store(&adviseUnused, madviseUnsupported)
		fallthrough
	case madviseUnsupported:
		// Since Linux 3.18, support for madvise is optional.
		// Fall back on mmap if it's not supported.
		// _MAP_ANON|_MAP_FIXED|_MAP_PRIVATE will unmap all the

	ready, err := p.blockUntilWaitable()
	if err != nil {
		return nil, err
	}
	if ready {
		// Mark the process done now, before the call to Wait4,
		// so that Process.pidSignal will not send a signal.
		p.pidDeactivate(statusDone)
		// Acquire a write lock on sigMu to wait for any
		// active call to the signal method to complete.
		p.sigMu.Lock()
		p.sigMu.Unlock()
	}

	var (
		status syscall.WaitStatus

		// Something wrong with socket(), fall back to checking the kernel version.
		major, minor := KernelVersion()
		if runtime.GOOS == "illumos" {
			return major > 5 || (major == 5 && minor >= 11) // minimal requirement is SunOS 5.11
		}
		return major > 11 || (major == 11 && minor >= 4)
	}
	return false
})

// SupportAccept4 tests whether accept4 system call is available.

	RET

noswitch:
	// already on system stack; tail call the function
	// Using a tail call here cleans up tracebacks since we won't stop
	// at an intermediate systemstack.
	MOVL	DI, DX
	MOVL	0(DI), DI
	JMP	DI

bad:
	// Bad: g is not gsignal, not g0, not curg. What is it?
	// Hide call from linker nosplit analysis.
	MOVL	$runtime·badsystemstack(SB), AX
	CALL	AX
	INT	$3

// atomicwb performs a write barrier before an atomic pointer write.
// The caller should guard the call with "if writeBarrier.enabled".
//
// atomicwb should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/bytedance/gopkg
//   - github.com/songzhibin97/gkit
//
// Do not remove or change the type signature.

	MOVW	(g_sched+gobuf_sp)(g), R1
	MOVW	R1, R29

	// call target function
	MOVW	0(REGCTXT), R4	// code pointer
	JAL	(R4)

	// switch back to g
	MOVW	g_m(g), R1
	MOVW	m_curg(R1), g
	JAL	runtime·save_g(SB)
	MOVW	(g_sched+gobuf_sp)(g), R29
	MOVW	R0, (g_sched+gobuf_sp)(g)
	RET

noswitch:
	// already on m stack, just call directly
	// Using a tail call here cleans up tracebacks since we won't stop

// value of mheap_.arena_used. (See issue #9984.)
//
//
// Stack writes:
//
// The compiler omits write barriers for writes to the current frame,
// but if a stack pointer has been passed down the call stack, the
// compiler will generate a write barrier for writes through that
// pointer (because it doesn't know it's not a heap pointer).
//
//
// Global writes:
//

	MOVV	(g_sched+gobuf_sp)(g), R19
	MOVV	R19, R3

	// call target function
	MOVV	0(REGCTXT), R6	// code pointer
	JAL	(R6)

	// switch back to g
	MOVV	g_m(g), R4
	MOVV	m_curg(R4), g
	JAL	runtime·save_g(SB)
	MOVV	(g_sched+gobuf_sp)(g), R3
	MOVV	R0, (g_sched+gobuf_sp)(g)
	RET

noswitch:
	// already on m stack, just call directly
	// Using a tail call here cleans up tracebacks since we won't stop

// If all is set, print all goroutine stacks. Otherwise, print just the current goroutine.
// If crash is set, crash (core dump, etc) after tracebacking.
//
//go:nosplit
func gotraceback() (level int32, all, crash bool) {
	gp := getg()
	t := atomic.Load(&traceback_cache)
	crash = t&tracebackCrash != 0
	all = gp.m.throwing >= throwTypeUser || t&tracebackAll != 0
	if gp.m.traceback != 0 {
		level = int32(gp.m.traceback)

	fn funcInfo

	// pc is the program counter within fn.
	//
	// The meaning of this is subtle:
	//
	// - Typically, this frame performed a regular function call
	//   and this is the return PC (just after the CALL
	//   instruction). In this case, pc-1 reflects the CALL
	//   instruction itself and is the correct source of symbolic
	//   information.
	//
	// - If this frame "called" sigpanic, then pc is the