// We won't get a nested signal.
	MOVBZ	runtime·iscgo(SB), R22
	CMP	R22, $0
	BNE	nosaveg
	MOVD	m_gsignal(R21), R22	// g.m.gsignal
	CMP	R22, $0
	BEQ	nosaveg

	CMP	g, R22
	BEQ	nosaveg
	MOVD	(g_stack+stack_lo)(R22), R22 // g.m.gsignal.stack.lo
	MOVD	g, (R22)

	BL	(CTR)	// Call from VDSO

	MOVD	$0, (R22)	// clear g slot, R22 is unchanged by C code

	JMP	finish

	MOVV	fn+0(FP), R19	// R19 = fn
	MOVV	R19, REGCTXT		// context
	MOVV	g_m(g), R4	// R4 = m

	MOVV	m_gsignal(R4), R5	// R5 = gsignal
	BEQ	g, R5, noswitch

	MOVV	m_g0(R4), R5	// R5 = g0
	BEQ	g, R5, noswitch

	MOVV	m_curg(R4), R6
	BEQ	g, R6, switch

	// Bad: g is not gsignal, not g0, not curg. What is it?
	// Hide call from linker nosplit analysis.
	MOVV	$runtime·badsystemstack(SB), R7
	JAL	(R7)

	// Also don't save g if we are already on the signal stack.
	// We won't get a nested signal.
	MOVBU	runtime·iscgo(SB), R22
	CBNZ	R22, nosaveg
	MOVD	m_gsignal(R21), R22          // g.m.gsignal
	CBZ	R22, nosaveg
	CMP	g, R22
	BEQ	nosaveg
	MOVD	(g_stack+stack_lo)(R22), R22 // g.m.gsignal.stack.lo
	MOVD	g, (R22)

	BL	(R2)

	MOVD	ZR, (R22)  // clear g slot, R22 is unchanged by C code

	B	finish

nosaveg:

TEXT runtime·systemstack(SB),NOSPLIT,$0-4
	MOVW	fn+0(FP), R0	// R0 = fn
	MOVW	g_m(g), R1	// R1 = m

	MOVW	m_gsignal(R1), R2	// R2 = gsignal
	CMP	g, R2
	B.EQ	noswitch

	MOVW	m_g0(R1), R2	// R2 = g0
	CMP	g, R2
	B.EQ	noswitch

	MOVW	m_curg(R1), R3
	CMP	g, R3
	B.EQ	switch

	// Bad: g is not gsignal, not g0, not curg. What is it?
	// Hide call from linker nosplit analysis.
	MOVW	$runtime·badsystemstack(SB), R0

	// Cannot grow scheduler stack (m->g0).
	Get g
	Get R2
	I64Eq
	If
		CALLNORESUME runtime·badmorestackg0(SB)
		CALLNORESUME runtime·abort(SB)
	End

	// Cannot grow signal stack (m->gsignal).
	Get g
	I64Load m_gsignal(R1)
	I64Eq
	If
		CALLNORESUME runtime·badmorestackgsignal(SB)
		CALLNORESUME runtime·abort(SB)
	End

	// Called from f.
	// Set m->morebuf to f's caller.

	// We get called to create new OS threads too, and those
	// come in on the m->g0 stack already. Or we might already
	// be on the m->gsignal stack.
	get_tls(CX)
	MOVL	g(CX), DI
	CMPL	DI, $0
	JEQ	nosave	// Don't even have a G yet.
	MOVL	g_m(DI), BP
	CMPL	DI, m_gsignal(BP)
	JEQ	noswitch
	MOVL	m_g0(BP), SI
	CMPL	DI, SI
	JEQ	noswitch
	CALL	gosave_systemstack_switch<>(SB)
	get_tls(CX)
	MOVL	SI, g(CX)

	MOVD	fn+0(FP), R3	// R3 = fn
	MOVD	R3, R11		// context
	MOVD	g_m(g), R4	// R4 = m

	MOVD	m_gsignal(R4), R5	// R5 = gsignal
	CMP	g, R5
	BEQ	noswitch

	MOVD	m_g0(R4), R5	// R5 = g0
	CMP	g, R5
	BEQ	noswitch

	MOVD	m_curg(R4), R6
	CMP	g, R6
	BEQ	switch

	// Bad: g is not gsignal, not g0, not curg. What is it?
	// Hide call from linker nosplit analysis.
	MOVD	$runtime·badsystemstack(SB), R12

	MOVD	fn+0(FP), R3	// R3 = fn
	MOVD	R3, R26		// context
	MOVD	g_m(g), R4	// R4 = m

	MOVD	m_gsignal(R4), R5	// R5 = gsignal
	CMP	g, R5
	BEQ	noswitch

	MOVD	m_g0(R4), R5	// R5 = g0
	CMP	g, R5
	BEQ	noswitch

	MOVD	m_curg(R4), R6
	CMP	g, R6
	BEQ	switch

	// Bad: g is not gsignal, not g0, not curg. What is it?
	// Hide call from linker nosplit analysis.
	MOVD	$runtime·badsystemstack(SB), R3

	// bother saving g.
	MOVW	m_gsignal(R6), R7          // g.m.gsignal
	CMP	$0, R7
	BEQ	nosaveg
	// Don't save g if we are already on the signal stack, as we won't get
	// a nested signal.
	CMP	g, R7
	BEQ	nosaveg
	// If we don't have a signal stack, we won't receive signal, so don't
	// bother saving g.
	MOVW	(g_stack+stack_lo)(R7), R7 // g.m.gsignal.stack.lo
	CMP	$0, R7
	BEQ	nosaveg
	MOVW	g, (R7)

	// iOS always use the main stack to run the signal handler.
	// We need to switch to gsignal ourselves.
	MOVD	g_m(g), R11
	MOVD	m_gsignal(R11), R5
	MOVD	(g_stack+stack_hi)(R5), R6

nog:
	// Restore arguments.
	MOVW	(8*1)(RSP), R0
	MOVD	(8*2)(RSP), R1
	MOVD	(8*3)(RSP), R2

	// Reserve space for args and the stack pointer on the
	// gsignal stack.
	SUB	$48, R6
	// Save stack pointer.
	MOVD	RSP, R4