stack overflow (morestack).

For example, deferproc might call malloc, which does one of the
above checks (without allocating a full frame), which might trigger
a call to morestack.  This sequence needs to fit in the bottom
section of the stack.  On amd64, morestack's frame is 40 bytes, and
deferproc's frame is 56 bytes.  That fits well within the
StackGuard - StackSmall bytes at the bottom.

	bls.To.SetTarget(movw)

	// BL runtime.morestack
	call := obj.Appendp(movw, c.newprog)
	call.As = obj.ACALL
	call.To.Type = obj.TYPE_BRANCH
	morestack := "runtime.morestack"
	switch {
	case c.cursym.CFunc():
		morestack = "runtime.morestackc"
	case !c.cursym.Func().Text.From.Sym.NeedCtxt():
		morestack = "runtime.morestack_noctxt"
	}
	call.To.Sym = c.ctxt.Lookup(morestack)

	// Spill the register args that could be clobbered by the
	// morestack code
	p = c.cursym.Func().SpillRegisterArgs(p, c.newprog)

	// JAL	runtime.morestack(SB)
	p = obj.Appendp(p, c.newprog)

	p.As = AJAL
	p.To.Type = obj.TYPE_BRANCH
	if c.cursym.CFunc() {
		p.To.Sym = c.ctxt.Lookup("runtime.morestackc")
	} else if !c.cursym.Func().Text.From.Sym.NeedCtxt() {

	}

	// BL	runtime.morestack(SB)
	call := obj.Appendp(debug, c.newprog)
	call.As = ABL
	call.To.Type = obj.TYPE_BRANCH
	morestack := "runtime.morestack"
	switch {
	case c.cursym.CFunc():
		morestack = "runtime.morestackc"
	case !c.cursym.Func().Text.From.Sym.NeedCtxt():
		morestack = "runtime.morestack_noctxt"
	}
	call.To.Sym = c.ctxt.Lookup(morestack)

	var morestacksym *obj.LSym
	if c.cursym.CFunc() {
		morestacksym = c.ctxt.Lookup("runtime.morestackc")
	} else if !c.cursym.Func().Text.From.Sym.NeedCtxt() {
		morestacksym = c.ctxt.Lookup("runtime.morestack_noctxt")
	} else {
		morestacksym = c.ctxt.Lookup("runtime.morestack")
	}

	if NeedTOCpointer(c.ctxt) {
		// In PPC64 PIC code, R2 is used as TOC pointer derived from R12

	call.As = obj.ACALL
	call.To.Type = obj.TYPE_BRANCH
	call.To.Name = obj.NAME_EXTERN
	morestack := "runtime.morestack"
	switch {
	case cursym.CFunc():
		morestack = "runtime.morestackc"
	case !cursym.Func().Text.From.Sym.NeedCtxt():
		morestack = "runtime.morestack_noctxt"
	}
	call.To.Sym = ctxt.Lookup(morestack)
	// When compiling 386 code for dynamic linking, the call needs to be adjusted

	// stackguard1 is the stack pointer compared in the //go:systemstack stack growth prologue.
	// It is stack.lo+StackGuard on g0 and gsignal stacks.
	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
	stack       stack   // offset known to runtime/cgo
	stackguard0 uintptr // offset known to liblink
	stackguard1 uintptr // offset known to liblink

	CALL

	// should never return
	CALL	runtime·abort(SB)
	UNDEF

// Called during function prolog when more stack is needed.
//
// The traceback routines see morestack on a g0 as being
// the top of a stack (for example, morestack calling newstack
// calling the scheduler calling newm calling gc), so we must
// record an argument size. For that purpose, it has no arguments.
TEXT runtime·morestack(SB), NOSPLIT, $0-0

	}
	return n
}

// nosplit to avoid preemption or morestack spilling registers.
//
//go:nosplit
//go:noinline
func testTracebackArgs10(a, b, c, d, e int32) int {
	// no use of any args
	return runtime.Stack(testTracebackArgsBuf[:], false)
}

// norace to avoid race instrumentation changing spill locations.
// nosplit to avoid preemption or morestack spilling registers.
//
//go:norace
//go:nosplit

	CALL	runtime·abort(SB)
	UNDEF

/*
 * support for morestack
 */

// Called during function prolog when more stack is needed.
// Called with return address (i.e. caller's PC) in X5 (aka T0),
// and the LR register contains the caller's LR.
//
// The traceback routines see morestack on a g0 as being
// the top of a stack (for example, morestack calling newstack