// void tstart(M *newm);
TEXT tstart<>(SB),NOSPLIT,$8-4
	MOVL	newm+0(FP), CX		// m
	MOVL	m_g0(CX), DX		// g

	// Layout new m scheduler stack on os stack.
	MOVL	SP, AX
	MOVL	AX, (g_stack+stack_hi)(DX)
	SUBL	$(64*1024), AX		// initial stack size (adjusted later)
	MOVL	AX, (g_stack+stack_lo)(DX)
	ADDL	$const_stackGuard, AX
	MOVL	AX, g_stackguard0(DX)
	MOVL	AX, g_stackguard1(DX)

	// Set up tls.
	LEAL	m_tls(CX), DI

	MOVW	m_g0(R0), g
	MOVW	R0, g_m(g)
	BL	runtime·save_g(SB)

	// Layout new m scheduler stack on os stack.
	MOVW	R13, R0
	MOVW	R0, g_stack+stack_hi(g)
	SUB	$(64*1024), R0
	MOVW	R0, (g_stack+stack_lo)(g)
	MOVW	R0, g_stackguard0(g)
	MOVW	R0, g_stackguard1(g)

	BL	runtime·emptyfunc(SB)	// fault if stack check is wrong
	BL	runtime·mstart(SB)

	// Exit the thread.
	MOVW	$0, R0

	EvGoBlockRecv       = 23 // goroutine blocks on chan recv [timestamp, stack]
	EvGoBlockSelect     = 24 // goroutine blocks on select [timestamp, stack]
	EvGoBlockSync       = 25 // goroutine blocks on Mutex/RWMutex [timestamp, stack]
	EvGoBlockCond       = 26 // goroutine blocks on Cond [timestamp, stack]
	EvGoBlockNet        = 27 // goroutine blocks on network [timestamp, stack]
	EvGoSysCall         = 28 // syscall enter [timestamp, stack]

	BR	runtime·badmcall2(SB)

// systemstack_switch is a dummy routine that systemstack leaves at the bottom
// of the G stack. We need to distinguish the routine that
// lives at the bottom of the G stack from the one that lives
// at the top of the system stack because the one at the top of
// the system stack terminates the stack walk (see topofstack()).
TEXT runtime·systemstack_switch(SB), NOSPLIT, $0-0

	MOVD	RSP, R13
	SUB	$16, R13
	MOVD	R13, RSP
	MOVD	R4, 0(RSP)	// save old g on stack
	MOVD	(g_stack+stack_hi)(R4), R4
	SUB	R2, R4
	MOVD	R4, 8(RSP)	// save depth in old g stack (can't just save SP, as stack might be copied during a callback)
	BL	(R1)
	MOVD	R0, R9

	// Restore g, stack pointer. R0 is errno, so don't touch it
	MOVD	0(RSP), g
	BL	runtime·save_g(SB)
	MOVD	(g_stack+stack_hi)(g), R5

	MOVL	AX, ret+4(FP)
	RET

TEXT runtime·tstart_plan9(SB),NOSPLIT,$4
	MOVL	newm+0(FP), CX
	MOVL	m_g0(CX), DX

	// Layout new m scheduler stack on os stack.
	MOVL	SP, AX
	MOVL	AX, (g_stack+stack_hi)(DX)
	SUBL	$(64*1024), AX		// stack size
	MOVL	AX, (g_stack+stack_lo)(DX)
	MOVL	AX, g_stackguard0(DX)
	MOVL	AX, g_stackguard1(DX)

	// Initialize procid from TOS struct.
	MOVL	_tos(SB), AX
	MOVL	48(AX), AX

	JMP	AX
	RET

// systemstack_switch is a dummy routine that systemstack leaves at the bottom
// of the G stack. We need to distinguish the routine that
// lives at the bottom of the G stack from the one that lives
// at the top of the system stack because the one at the top of
// the system stack terminates the stack walk (see topofstack()).
TEXT runtime·systemstack_switch(SB), NOSPLIT, $0-0
	RET

// func systemstack(fn func())

	PUSH_REGS_HOST_TO_ABI0()

	// CX contains first arg newm
	MOVQ	m_g0(CX), DX		// g

	// Layout new m scheduler stack on os stack.
	MOVQ	SP, AX
	MOVQ	AX, (g_stack+stack_hi)(DX)
	SUBQ	$(64*1024), AX		// initial stack size (adjusted later)
	MOVQ	AX, (g_stack+stack_lo)(DX)
	ADDQ	$const_stackGuard, AX
	MOVQ	AX, g_stackguard0(DX)
	MOVQ	AX, g_stackguard1(DX)

	// Set up tls.
	LEAQ	m_tls(CX), DI

	// and without worrying about the stack moving out from under us
	// (because we're on a system stack, not a goroutine stack).
	// The above code could be used directly if already on a system stack,
	// but then the only path through this code would be a rare case on Solaris.
	// Using this code for all "already on system stack" calls exercises it more,
	// which should help keep it correct.
	SUBQ	$16, SP

		data="hello world\x00"

These events are identified in their spec by the HasData flag.

The second special case consists of stack events. These events are identified
by the IsStack flag. These events also have a trailing unsigned integer argument
describing the number of stack frame descriptors that follow. Each stack frame
descriptor is on its own line following the event, consisting of four signed