src/runtime/asm_mipsx.s

// Copyright 2016 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.

// +build mips mipsle

#include "go_asm.h"
#include "go_tls.h"
#include "funcdata.h"
#include "textflag.h"

#define	REGCTXT	R22

TEXT runtime·rt0_go(SB),NOSPLIT,$0
	// R29 = stack; R4 = argc; R5 = argv

	ADDU	$-12, R29
	MOVW	R4, 4(R29)	// argc
	MOVW	R5, 8(R29)	// argv

	// create istack out of the given (operating system) stack.
	// _cgo_init may update stackguard.
	MOVW	$runtime·g0(SB), g
	MOVW	$(-64*1024), R23
	ADD	R23, R29, R1
	MOVW	R1, g_stackguard0(g)
	MOVW	R1, g_stackguard1(g)
	MOVW	R1, (g_stack+stack_lo)(g)
	MOVW	R29, (g_stack+stack_hi)(g)

	// if there is a _cgo_init, call it using the gcc ABI.
	MOVW	_cgo_init(SB), R25
	BEQ	R25, nocgo
	ADDU	$-16, R29
	MOVW	R0, R7	// arg 3: not used
	MOVW	R0, R6	// arg 2: not used
	MOVW	$setg_gcc<>(SB), R5	// arg 1: setg
	MOVW	g, R4	// arg 0: G
	JAL	(R25)
	ADDU	$16, R29

nocgo:
	// update stackguard after _cgo_init
	MOVW	(g_stack+stack_lo)(g), R1
	ADD	$const__StackGuard, R1
	MOVW	R1, g_stackguard0(g)
	MOVW	R1, g_stackguard1(g)

	// set the per-goroutine and per-mach "registers"
	MOVW	$runtime·m0(SB), R1

	// save m->g0 = g0
	MOVW	g, m_g0(R1)
	// save m0 to g0->m
	MOVW	R1, g_m(g)

	JAL	runtime·check(SB)

	// args are already prepared
	JAL	runtime·args(SB)
	JAL	runtime·osinit(SB)
	JAL	runtime·schedinit(SB)

	// create a new goroutine to start program
	MOVW	$runtime·mainPC(SB), R1	// entry
	ADDU	$-12, R29
	MOVW	R1, 8(R29)
	MOVW	R0, 4(R29)
	MOVW	R0, 0(R29)
	JAL	runtime·newproc(SB)
	ADDU	$12, R29

	// start this M
	JAL	runtime·mstart(SB)

	UNDEF
	RET

DATA	runtime·mainPC+0(SB)/4,$runtime·main(SB)
GLOBL	runtime·mainPC(SB),RODATA,$4

TEXT runtime·breakpoint(SB),NOSPLIT,$0-0
	BREAK
	RET

TEXT runtime·asminit(SB),NOSPLIT,$0-0
	RET

/*
 *  go-routine
 */

// void gosave(Gobuf*)
// save state in Gobuf; setjmp
TEXT runtime·gosave(SB),NOSPLIT|NOFRAME,$0-4
	MOVW	buf+0(FP), R1
	MOVW	R29, gobuf_sp(R1)
	MOVW	R31, gobuf_pc(R1)
	MOVW	g, gobuf_g(R1)
	MOVW	R0, gobuf_lr(R1)
	MOVW	R0, gobuf_ret(R1)
	// Assert ctxt is zero. See func save.
	MOVW	gobuf_ctxt(R1), R1
	BEQ	R1, 2(PC)
	JAL	runtime·badctxt(SB)
	RET

// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB),NOSPLIT,$8-4
	MOVW	buf+0(FP), R3
	MOVW	gobuf_g(R3), g	// make sure g is not nil
	JAL	runtime·save_g(SB)

	MOVW	0(g), R2
	MOVW	gobuf_sp(R3), R29
	MOVW	gobuf_lr(R3), R31
	MOVW	gobuf_ret(R3), R1
	MOVW	gobuf_ctxt(R3), REGCTXT
	MOVW	R0, gobuf_sp(R3)
	MOVW	R0, gobuf_ret(R3)
	MOVW	R0, gobuf_lr(R3)
	MOVW	R0, gobuf_ctxt(R3)
	MOVW	gobuf_pc(R3), R4
	JMP	(R4)

// void mcall(fn func(*g))
// Switch to m->g0's stack, call fn(g).
// Fn must never return. It should gogo(&g->sched)
// to keep running g.
TEXT runtime·mcall(SB),NOSPLIT|NOFRAME,$0-4
	// Save caller state in g->sched
	MOVW	R29, (g_sched+gobuf_sp)(g)
	MOVW	R31, (g_sched+gobuf_pc)(g)
	MOVW	R0, (g_sched+gobuf_lr)(g)
	MOVW	g, (g_sched+gobuf_g)(g)

	// Switch to m->g0 & its stack, call fn.
	MOVW	g, R1
	MOVW	g_m(g), R3
	MOVW	m_g0(R3), g
	JAL	runtime·save_g(SB)
	BNE	g, R1, 2(PC)
	JMP	runtime·badmcall(SB)
	MOVW	fn+0(FP), REGCTXT	// context
	MOVW	0(REGCTXT), R4	// code pointer
	MOVW	(g_sched+gobuf_sp)(g), R29	// sp = m->g0->sched.sp
	ADDU	$-8, R29	// make room for 1 arg and fake LR
	MOVW	R1, 4(R29)
	MOVW	R0, 0(R29)
	JAL	(R4)
	JMP	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
	UNDEF
	JAL	(R31)	// make sure this function is not leaf
	RET

// func systemstack(fn func())
TEXT runtime·systemstack(SB),NOSPLIT,$0-4
	MOVW	fn+0(FP), R1	// R1 = fn
	MOVW	R1, REGCTXT	// context
	MOVW	g_m(g), R2	// R2 = m

	MOVW	m_gsignal(R2), R3	// R3 = gsignal
	BEQ	g, R3, noswitch

	MOVW	m_g0(R2), R3	// R3 = g0
	BEQ	g, R3, noswitch

	MOVW	m_curg(R2), R4
	BEQ	g, R4, switch

	// Bad: g is not gsignal, not g0, not curg. What is it?
	// Hide call from linker nosplit analysis.
	MOVW	$runtime·badsystemstack(SB), R4
	JAL	(R4)
	JAL	runtime·abort(SB)

switch:
	// save our state in g->sched.  Pretend to
	// be systemstack_switch if the G stack is scanned.
	MOVW	$runtime·systemstack_switch(SB), R4
	ADDU	$8, R4	// get past prologue
	MOVW	R4, (g_sched+gobuf_pc)(g)
	MOVW	R29, (g_sched+gobuf_sp)(g)
	MOVW	R0, (g_sched+gobuf_lr)(g)
	MOVW	g, (g_sched+gobuf_g)(g)

	// switch to g0
	MOVW	R3, g
	JAL	runtime·save_g(SB)
	MOVW	(g_sched+gobuf_sp)(g), R1
	// make it look like mstart called systemstack on g0, to stop traceback
	ADDU	$-4, R1
	MOVW	$runtime·mstart(SB), R2
	MOVW	R2, 0(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
	// at an intermediate systemstack.
	MOVW	0(REGCTXT), R4	// code pointer
	MOVW	0(R29), R31	// restore LR
	ADD	$4, R29
	JMP	(R4)

/*
 * support for morestack
 */

// Called during function prolog when more stack is needed.
// Caller has already loaded:
// R1: framesize, R2: argsize, R3: LR
//
// 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|NOFRAME,$0-0
	// Cannot grow scheduler stack (m->g0).
	MOVW	g_m(g), R7
	MOVW	m_g0(R7), R8
	BNE	g, R8, 3(PC)
	JAL	runtime·badmorestackg0(SB)
	JAL	runtime·abort(SB)

	// Cannot grow signal stack (m->gsignal).
	MOVW	m_gsignal(R7), R8
	BNE	g, R8, 3(PC)
	JAL	runtime·badmorestackgsignal(SB)
	JAL	runtime·abort(SB)

	// Called from f.
	// Set g->sched to context in f.
	MOVW	R29, (g_sched+gobuf_sp)(g)
	MOVW	R31, (g_sched+gobuf_pc)(g)
	MOVW	R3, (g_sched+gobuf_lr)(g)
	MOVW	REGCTXT, (g_sched+gobuf_ctxt)(g)

	// Called from f.
	// Set m->morebuf to f's caller.
	MOVW	R3, (m_morebuf+gobuf_pc)(R7)	// f's caller's PC
	MOVW	R29, (m_morebuf+gobuf_sp)(R7)	// f's caller's SP
	MOVW	g, (m_morebuf+gobuf_g)(R7)

	// Call newstack on m->g0's stack.
	MOVW	m_g0(R7), g
	JAL	runtime·save_g(SB)
	MOVW	(g_sched+gobuf_sp)(g), R29
	// Create a stack frame on g0 to call newstack.
	MOVW	R0, -4(R29)	// Zero saved LR in frame
	ADDU	$-4, R29
	JAL	runtime·newstack(SB)

	// Not reached, but make sure the return PC from the call to newstack
	// is still in this function, and not the beginning of the next.
	UNDEF

TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
	MOVW	R0, REGCTXT
	JMP	runtime·morestack(SB)

// reflectcall: call a function with the given argument list
// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
// we don't have variable-sized frames, so we use a small number
// of constant-sized-frame functions to encode a few bits of size in the pc.

#define DISPATCH(NAME,MAXSIZE)	\
	MOVW	$MAXSIZE, R23;	\
	SGTU	R1, R23, R23;	\
	BNE	R23, 3(PC);	\
	MOVW	$NAME(SB), R4;	\
	JMP	(R4)

TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-20
	MOVW	argsize+12(FP), R1

	DISPATCH(runtime·call16, 16)
	DISPATCH(runtime·call32, 32)
	DISPATCH(runtime·call64, 64)
	DISPATCH(runtime·call128, 128)
	DISPATCH(runtime·call256, 256)
	DISPATCH(runtime·call512, 512)
	DISPATCH(runtime·call1024, 1024)
	DISPATCH(runtime·call2048, 2048)
	DISPATCH(runtime·call4096, 4096)
	DISPATCH(runtime·call8192, 8192)
	DISPATCH(runtime·call16384, 16384)
	DISPATCH(runtime·call32768, 32768)
	DISPATCH(runtime·call65536, 65536)
	DISPATCH(runtime·call131072, 131072)
	DISPATCH(runtime·call262144, 262144)
	DISPATCH(runtime·call524288, 524288)
	DISPATCH(runtime·call1048576, 1048576)
	DISPATCH(runtime·call2097152, 2097152)
	DISPATCH(runtime·call4194304, 4194304)
	DISPATCH(runtime·call8388608, 8388608)
	DISPATCH(runtime·call16777216, 16777216)
	DISPATCH(runtime·call33554432, 33554432)
	DISPATCH(runtime·call67108864, 67108864)
	DISPATCH(runtime·call134217728, 134217728)
	DISPATCH(runtime·call268435456, 268435456)
	DISPATCH(runtime·call536870912, 536870912)
	DISPATCH(runtime·call1073741824, 1073741824)
	MOVW	$runtime·badreflectcall(SB), R4
	JMP	(R4)

#define CALLFN(NAME,MAXSIZE)	\
TEXT NAME(SB),WRAPPER,$MAXSIZE-20;	\
	NO_LOCAL_POINTERS;	\
	/* copy arguments to stack */		\
	MOVW	arg+8(FP), R1;	\
	MOVW	argsize+12(FP), R2;	\
	MOVW	R29, R3;	\
	ADDU	$4, R3;	\
	ADDU	R3, R2;	\
	BEQ	R3, R2, 6(PC);	\
	MOVBU	(R1), R4;	\
	ADDU	$1, R1;	\
	MOVBU	R4, (R3);	\
	ADDU	$1, R3;	\
	JMP	-5(PC);	\
	/* call function */			\
	MOVW	f+4(FP), REGCTXT;	\
	MOVW	(REGCTXT), R4;	\
	PCDATA	$PCDATA_StackMapIndex, $0;	\
	JAL	(R4);	\
	/* copy return values back */		\
	MOVW	argtype+0(FP), R5;	\
	MOVW	arg+8(FP), R1;	\
	MOVW	n+12(FP), R2;	\
	MOVW	retoffset+16(FP), R4;	\
	ADDU	$4, R29, R3;	\
	ADDU	R4, R3;	\
	ADDU	R4, R1;	\
	SUBU	R4, R2;	\
	JAL	callRet<>(SB);		\
	RET

// callRet copies return values back at the end of call*. This is a
// separate function so it can allocate stack space for the arguments
// to reflectcallmove. It does not follow the Go ABI; it expects its
// arguments in registers.
TEXT callRet<>(SB), NOSPLIT, $16-0
	MOVW	R5, 4(R29)
	MOVW	R1, 8(R29)
	MOVW	R3, 12(R29)
	MOVW	R2, 16(R29)
	JAL	runtime·reflectcallmove(SB)
	RET

CALLFN(·call16, 16)
CALLFN(·call32, 32)
CALLFN(·call64, 64)
CALLFN(·call128, 128)
CALLFN(·call256, 256)
CALLFN(·call512, 512)
CALLFN(·call1024, 1024)
CALLFN(·call2048, 2048)
CALLFN(·call4096, 4096)
CALLFN(·call8192, 8192)
CALLFN(·call16384, 16384)
CALLFN(·call32768, 32768)
CALLFN(·call65536, 65536)
CALLFN(·call131072, 131072)
CALLFN(·call262144, 262144)
CALLFN(·call524288, 524288)
CALLFN(·call1048576, 1048576)
CALLFN(·call2097152, 2097152)
CALLFN(·call4194304, 4194304)
CALLFN(·call8388608, 8388608)
CALLFN(·call16777216, 16777216)
CALLFN(·call33554432, 33554432)
CALLFN(·call67108864, 67108864)
CALLFN(·call134217728, 134217728)
CALLFN(·call268435456, 268435456)
CALLFN(·call536870912, 536870912)
CALLFN(·call1073741824, 1073741824)

TEXT runtime·procyield(SB),NOSPLIT,$0-4
	RET

// void jmpdefer(fv, sp);
// called from deferreturn.
// 1. grab stored LR for caller
// 2. sub 8 bytes to get back to JAL deferreturn
// 3. JMP to fn
TEXT runtime·jmpdefer(SB),NOSPLIT,$0-8
	MOVW	0(R29), R31
	ADDU	$-8, R31

	MOVW	fv+0(FP), REGCTXT
	MOVW	argp+4(FP), R29
	ADDU	$-4, R29
	NOR	R0, R0	// prevent scheduling
	MOVW	0(REGCTXT), R4
	JMP	(R4)

// Save state of caller into g->sched. Smashes R1.
TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
	MOVW	R31, (g_sched+gobuf_pc)(g)
	MOVW	R29, (g_sched+gobuf_sp)(g)
	MOVW	R0, (g_sched+gobuf_lr)(g)
	MOVW	R0, (g_sched+gobuf_ret)(g)
	// Assert ctxt is zero. See func save.
	MOVW	(g_sched+gobuf_ctxt)(g), R1
	BEQ	R1, 2(PC)
	JAL	runtime·badctxt(SB)
	RET

// func asmcgocall(fn, arg unsafe.Pointer) int32
// Call fn(arg) on the scheduler stack,
// aligned appropriately for the gcc ABI.
// See cgocall.go for more details.
TEXT ·asmcgocall(SB),NOSPLIT,$0-12
	MOVW	fn+0(FP), R25
	MOVW	arg+4(FP), R4

	MOVW	R29, R3	// save original stack pointer
	MOVW	g, R2

	// Figure out if we need to switch to m->g0 stack.
	// We get called to create new OS threads too, and those
	// come in on the m->g0 stack already.
	MOVW	g_m(g), R5
	MOVW	m_g0(R5), R6
	BEQ	R6, g, g0

	JAL	gosave<>(SB)
	MOVW	R6, g
	JAL	runtime·save_g(SB)
	MOVW	(g_sched+gobuf_sp)(g), R29

	// Now on a scheduling stack (a pthread-created stack).
g0:
	// Save room for two of our pointers and O32 frame.
	ADDU	$-24, R29
	AND	$~7, R29	// O32 ABI expects 8-byte aligned stack on function entry
	MOVW	R2, 16(R29)	// save old g on stack
	MOVW	(g_stack+stack_hi)(R2), R2
	SUBU	R3, R2
	MOVW	R2, 20(R29)	// save depth in old g stack (can't just save SP, as stack might be copied during a callback)
	JAL	(R25)

	// Restore g, stack pointer. R2 is return value.
	MOVW	16(R29), g
	JAL	runtime·save_g(SB)
	MOVW	(g_stack+stack_hi)(g), R5
	MOVW	20(R29), R6
	SUBU	R6, R5
	MOVW	R5, R29

	MOVW	R2, ret+8(FP)
	RET

// cgocallback(void (*fn)(void*), void *frame, uintptr framesize)
// Turn the fn into a Go func (by taking its address) and call
// cgocallback_gofunc.
TEXT runtime·cgocallback(SB),NOSPLIT,$16-16
	MOVW	$fn+0(FP), R1
	MOVW	R1, 4(R29)
	MOVW	frame+4(FP), R1
	MOVW	R1, 8(R29)
	MOVW	framesize+8(FP), R1
	MOVW	R1, 12(R29)
	MOVW	ctxt+12(FP), R1
	MOVW	R1, 16(R29)
	MOVW	$runtime·cgocallback_gofunc(SB), R1
	JAL	(R1)
	RET

// cgocallback_gofunc(FuncVal*, void *frame, uintptr framesize, uintptr ctxt)
// See cgocall.go for more details.
TEXT ·cgocallback_gofunc(SB),NOSPLIT,$8-16
	NO_LOCAL_POINTERS

	// Load m and g from thread-local storage.
	MOVB	runtime·iscgo(SB), R1
	BEQ	R1, nocgo
	JAL	runtime·load_g(SB)
nocgo:

	// If g is nil, Go did not create the current thread.
	// Call needm to obtain one for temporary use.
	// In this case, we're running on the thread stack, so there's
	// lots of space, but the linker doesn't know. Hide the call from
	// the linker analysis by using an indirect call.
	BEQ	g, needm

	MOVW	g_m(g), R3
	MOVW	R3, savedm-4(SP)
	JMP	havem

needm:
	MOVW	g, savedm-4(SP) // g is zero, so is m.
	MOVW	$runtime·needm(SB), R4
	JAL	(R4)

	// Set m->sched.sp = SP, so that if a panic happens
	// during the function we are about to execute, it will
	// have a valid SP to run on the g0 stack.
	// The next few lines (after the havem label)
	// will save this SP onto the stack and then write
	// the same SP back to m->sched.sp. That seems redundant,
	// but if an unrecovered panic happens, unwindm will
	// restore the g->sched.sp from the stack location
	// and then systemstack will try to use it. If we don't set it here,
	// that restored SP will be uninitialized (typically 0) and
	// will not be usable.
	MOVW	g_m(g), R3
	MOVW	m_g0(R3), R1
	MOVW	R29, (g_sched+gobuf_sp)(R1)

havem:
	// Now there's a valid m, and we're running on its m->g0.
	// Save current m->g0->sched.sp on stack and then set it to SP.
	// Save current sp in m->g0->sched.sp in preparation for
	// switch back to m->curg stack.
	// NOTE: unwindm knows that the saved g->sched.sp is at 4(R29) aka savedsp-8(SP).
	MOVW	m_g0(R3), R1
	MOVW	(g_sched+gobuf_sp)(R1), R2
	MOVW	R2, savedsp-8(SP)
	MOVW	R29, (g_sched+gobuf_sp)(R1)

	// Switch to m->curg stack and call runtime.cgocallbackg.
	// Because we are taking over the execution of m->curg
	// but *not* resuming what had been running, we need to
	// save that information (m->curg->sched) so we can restore it.
	// We can restore m->curg->sched.sp easily, because calling
	// runtime.cgocallbackg leaves SP unchanged upon return.
	// To save m->curg->sched.pc, we push it onto the stack.
	// This has the added benefit that it looks to the traceback
	// routine like cgocallbackg is going to return to that
	// PC (because the frame we allocate below has the same
	// size as cgocallback_gofunc's frame declared above)
	// so that the traceback will seamlessly trace back into
	// the earlier calls.
	//
	// In the new goroutine, -4(SP) is unused (where SP refers to
	// m->curg's SP while we're setting it up, before we've adjusted it).
	MOVW	m_curg(R3), g
	JAL	runtime·save_g(SB)
	MOVW	(g_sched+gobuf_sp)(g), R2 // prepare stack as R2
	MOVW	(g_sched+gobuf_pc)(g), R4
	MOVW	R4, -12(R2)
	MOVW    ctxt+12(FP), R1
	MOVW    R1, -8(R2)
	MOVW	$-12(R2), R29
	JAL	runtime·cgocallbackg(SB)

	// Restore g->sched (== m->curg->sched) from saved values.
	MOVW	0(R29), R4
	MOVW	R4, (g_sched+gobuf_pc)(g)
	MOVW	$12(R29), R2
	MOVW	R2, (g_sched+gobuf_sp)(g)

	// Switch back to m->g0's stack and restore m->g0->sched.sp.
	// (Unlike m->curg, the g0 goroutine never uses sched.pc,
	// so we do not have to restore it.)
	MOVW	g_m(g), R3
	MOVW	m_g0(R3), g
	JAL	runtime·save_g(SB)
	MOVW	(g_sched+gobuf_sp)(g), R29
	MOVW	savedsp-8(SP), R2
	MOVW	R2, (g_sched+gobuf_sp)(g)

	// If the m on entry was nil, we called needm above to borrow an m
	// for the duration of the call. Since the call is over, return it with dropm.
	MOVW	savedm-4(SP), R3
	BNE	R3, droppedm
	MOVW	$runtime·dropm(SB), R4
	JAL	(R4)
droppedm:

	// Done!
	RET

// void setg(G*); set g. for use by needm.
// This only happens if iscgo, so jump straight to save_g
TEXT runtime·setg(SB),NOSPLIT,$0-4
	MOVW	gg+0(FP), g
	JAL	runtime·save_g(SB)
	RET

// void setg_gcc(G*); set g in C TLS.
// Must obey the gcc calling convention.
TEXT setg_gcc<>(SB),NOSPLIT,$0
	MOVW	R4, g
	JAL	runtime·save_g(SB)
	RET

TEXT runtime·abort(SB),NOSPLIT,$0-0
	UNDEF

// Not implemented.
TEXT runtime·aeshash(SB),NOSPLIT,$0
	UNDEF

// Not implemented.
TEXT runtime·aeshash32(SB),NOSPLIT,$0
	UNDEF

// Not implemented.
TEXT runtime·aeshash64(SB),NOSPLIT,$0
	UNDEF

// Not implemented.
TEXT runtime·aeshashstr(SB),NOSPLIT,$0
	UNDEF

TEXT runtime·return0(SB),NOSPLIT,$0
	MOVW	$0, R1
	RET

// Called from cgo wrappers, this function returns g->m->curg.stack.hi.
// Must obey the gcc calling convention.
TEXT _cgo_topofstack(SB),NOSPLIT|NOFRAME,$0
	// g (R30), R3 and REGTMP (R23) might be clobbered by load_g. R30 and R23
	// are callee-save in the gcc calling convention, so save them.
	MOVW	R23, R8
	MOVW	g, R9
	MOVW	R31, R10 // this call frame does not save LR

	JAL	runtime·load_g(SB)
	MOVW	g_m(g), R1
	MOVW	m_curg(R1), R1
	MOVW	(g_stack+stack_hi)(R1), R2 // return value in R2

	MOVW	R8, R23
	MOVW	R9, g
	MOVW	R10, R31

	RET

// The top-most function running on a goroutine
// returns to goexit+PCQuantum.
TEXT runtime·goexit(SB),NOSPLIT|NOFRAME,$0-0
	NOR	R0, R0	// NOP
	JAL	runtime·goexit1(SB)	// does not return
	// traceback from goexit1 must hit code range of goexit
	NOR	R0, R0	// NOP

TEXT ·checkASM(SB),NOSPLIT,$0-1
	MOVW	$1, R1
	MOVB	R1, ret+0(FP)
	RET

// gcWriteBarrier performs a heap pointer write and informs the GC.
//
// gcWriteBarrier does NOT follow the Go ABI. It takes two arguments:
// - R20 is the destination of the write
// - R21 is the value being written at R20.
// It clobbers R23 (the linker temp register).
// The act of CALLing gcWriteBarrier will clobber R31 (LR).
// It does not clobber any other general-purpose registers,
// but may clobber others (e.g., floating point registers).
TEXT runtime·gcWriteBarrier(SB),NOSPLIT,$104
	// Save the registers clobbered by the fast path.
	MOVW	R1, 100(R29)
	MOVW	R2, 104(R29)
	MOVW	g_m(g), R1
	MOVW	m_p(R1), R1
	MOVW	(p_wbBuf+wbBuf_next)(R1), R2
	// Increment wbBuf.next position.
	ADD	$8, R2
	MOVW	R2, (p_wbBuf+wbBuf_next)(R1)
	MOVW	(p_wbBuf+wbBuf_end)(R1), R1
	MOVW	R1, R23		// R23 is linker temp register
	// Record the write.
	MOVW	R21, -8(R2)	// Record value
	MOVW	(R20), R1	// TODO: This turns bad writes into bad reads.
	MOVW	R1, -4(R2)	// Record *slot
	// Is the buffer full?
	BEQ	R2, R23, flush
ret:
	MOVW	100(R29), R1
	MOVW	104(R29), R2
	// Do the write.
	MOVW	R21, (R20)
	RET

flush:
	// Save all general purpose registers since these could be
	// clobbered by wbBufFlush and were not saved by the caller.
	MOVW	R20, 4(R29)	// Also first argument to wbBufFlush
	MOVW	R21, 8(R29)	// Also second argument to wbBufFlush
	// R1 already saved
	// R2 already saved
	MOVW	R3, 12(R29)
	MOVW	R4, 16(R29)
	MOVW	R5, 20(R29)
	MOVW	R6, 24(R29)
	MOVW	R7, 28(R29)
	MOVW	R8, 32(R29)
	MOVW	R9, 36(R29)
	MOVW	R10, 40(R29)
	MOVW	R11, 44(R29)
	MOVW	R12, 48(R29)
	MOVW	R13, 52(R29)
	MOVW	R14, 56(R29)
	MOVW	R15, 60(R29)
	MOVW	R16, 64(R29)
	MOVW	R17, 68(R29)
	MOVW	R18, 72(R29)
	MOVW	R19, 76(R29)
	MOVW	R20, 80(R29)
	// R21 already saved
	// R22 already saved.
	MOVW	R22, 84(R29)
	// R23 is tmp register.
	MOVW	R24, 88(R29)
	MOVW	R25, 92(R29)
	// R26 is reserved by kernel.
	// R27 is reserved by kernel.
	MOVW	R28, 96(R29)
	// R29 is SP.
	// R30 is g.
	// R31 is LR, which was saved by the prologue.

	// This takes arguments R20 and R21.
	CALL	runtime·wbBufFlush(SB)

	MOVW	4(R29), R20
	MOVW	8(R29), R21
	MOVW	12(R29), R3
	MOVW	16(R29), R4
	MOVW	20(R29), R5
	MOVW	24(R29), R6
	MOVW	28(R29), R7
	MOVW	32(R29), R8
	MOVW	36(R29), R9
	MOVW	40(R29), R10
	MOVW	44(R29), R11
	MOVW	48(R29), R12
	MOVW	52(R29), R13
	MOVW	56(R29), R14
	MOVW	60(R29), R15
	MOVW	64(R29), R16
	MOVW	68(R29), R17
	MOVW	72(R29), R18
	MOVW	76(R29), R19
	MOVW	80(R29), R20
	MOVW	84(R29), R22
	MOVW	88(R29), R24
	MOVW	92(R29), R25
	MOVW	96(R29), R28
	JMP	ret