// Copyright 2018 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.

#include "go_asm.h"
#include "textflag.h"

// _rt0_wasm_js is not used itself. It only exists to mark the exported functions as alive.
TEXT _rt0_wasm_js(SB),NOSPLIT,$0
	I32Const $wasm_export_run(SB)
	Drop
	I32Const $wasm_export_resume(SB)
	Drop
	I32Const $wasm_export_getsp(SB)
	Drop

// wasm_export_run gets called from JavaScript. It initializes the Go runtime and executes Go code until it needs
// to wait for a callback. It does NOT follow the Go ABI. It has two WebAssembly parameters:
// R0: argc (i32)
// R1: argv (i32)
TEXT wasm_export_run(SB),NOSPLIT,$0
	MOVD $runtime·wasmStack+m0Stack__size(SB), SP

	Get SP
	Get R0 // argc
	I64ExtendUI32
	I64Store $0

	Get SP
	Get R1 // argv
	I64ExtendUI32
	I64Store $8

	I32Const $runtime·rt0_go(SB)
	I32Const $16
	I32ShrU
	Set PC_F

	I32Const $0
	Set PC_B

	Call wasm_pc_f_loop(SB)

	Return

// wasm_export_resume gets called from JavaScript. It resumes the execution of Go code until it needs to wait for
// a callback.
TEXT wasm_export_resume(SB),NOSPLIT,$0
	I32Const $runtime·handleCallback(SB)
	I32Const $16
	I32ShrU
	Set PC_F

	I32Const $0
	Set PC_B

	Call wasm_pc_f_loop(SB)

	Return

TEXT wasm_pc_f_loop(SB),NOSPLIT,$0
// Call the function for the current PC_F. Repeat until PAUSE != 0 indicates pause or exit.
// The WebAssembly stack may unwind, e.g. when switching goroutines.
// The Go stack on the linear memory is then used to jump to the correct functions
// with this loop, without having to restore the full WebAssembly stack.
loop:
	Loop
		Get PC_F
		CallIndirect $0
		Drop

		Get PAUSE
		I32Eqz
		BrIf loop
	End

	I32Const $0
	Set PAUSE

	Return

// wasm_export_getsp gets called from JavaScript to retrieve the SP.
TEXT wasm_export_getsp(SB),NOSPLIT,$0
	Get SP
	Return

TEXT runtime·pause(SB), NOSPLIT, $0-8
	MOVD newsp+0(FP), SP
	I32Const $1
	Set PAUSE
	RETUNWIND

TEXT runtime·exit(SB), NOSPLIT, $0-4
	Call runtime·wasmExit(SB)
	Drop
	I32Const $1
	Set PAUSE
	RETUNWIND

TEXT wasm_export_lib(SB),NOSPLIT,$0
	UNDEF