tinygo/src/runtime/runtime_wasm.go

// +build wasm

package runtime

import (
	"unsafe"
)

// Implements __wasi_iovec_t.
type __wasi_iovec_t struct {
	buf    unsafe.Pointer
	bufLen uint
}

//go:wasm-module wasi_unstable
//export fd_write
func fd_write(id uint32, iovs *__wasi_iovec_t, iovs_len uint, nwritten *uint) (errno uint)

func postinit() {}

const (
	putcharBufferSize = 120
	stdout            = 1
)

// Using global variables to avoid heap allocation.
var (
	putcharBuffer        = [putcharBufferSize]byte{}
	putcharPosition uint = 0
	putcharIOVec         = __wasi_iovec_t{
		buf: unsafe.Pointer(&putcharBuffer[0]),
	}
	putcharNWritten uint
)

func putchar(c byte) {
	putcharBuffer[putcharPosition] = c
	putcharPosition++

	if c == '\n' || putcharPosition >= putcharBufferSize {
		putcharIOVec.bufLen = putcharPosition
		fd_write(stdout, &putcharIOVec, 1, &putcharNWritten)
		putcharPosition = 0
	}
}

// Abort executes the wasm 'unreachable' instruction.
func abort() {
	trap()
}

// TinyGo does not yet support any form of parallelism on WebAssembly, so these
// can be left empty.

//go:linkname procPin sync/atomic.runtime_procPin
func procPin() {
}

//go:linkname procUnpin sync/atomic.runtime_procUnpin
func procUnpin() {
}