derpy derp jit for basic arithmetic in Go

gistfile1.go

package main

// int callGate(void* p) {
//    return ((int (*)())p)();
// }
import "C"

import (
	"os"
	"io"
	"fmt"
	"syscall"
	"unsafe"
	"bytes"
	"bufio"
	"unicode"
)

type Compiler struct {
	Buffer *bytes.Buffer
	Reader *bufio.Reader
	Curr   rune
}

func NewCompiler(in io.Reader) *Compiler {
	c := &Compiler{
		Buffer: bytes.NewBuffer([]byte{}),
                Reader: bufio.NewReader(in),
	}
	c.Next()
	return c
}

func (c *Compiler) Program() {
	//c.Buffer.WriteByte(0xcc) // INT3 debugger break
	c.Expression()
	fmt.Printf("retq\n")
	c.Buffer.WriteByte(0xc3)
}

func (c *Compiler) Expression() {
	c.Number()
	if c.Curr == '+' {
		fmt.Printf("push\t%%rax\n")
		c.Buffer.WriteByte(0x50)
		c.Next()
		c.Expression()
		fmt.Printf("pop\t%%rdi\n")
		c.Buffer.WriteByte(0x5f)
		fmt.Printf("add\t%%rdi,%%rax\n")
		c.Buffer.Write([]byte{0x48, 0x01, 0xf8})
	}
}

func (c *Compiler) Number() {
	var sum int32 = 0
	for unicode.IsDigit(c.Curr) {
		sum = sum*10 + int32(c.Curr)-'0'
		c.Next()
	}

	fmt.Printf("mov\t$%d,%%rax\n", sum)
	c.Buffer.Write([]byte{0x48, 0xc7, 0xc0})
	c.Buffer.Write([]byte{
		byte(sum & 0xff),
		byte((sum >> 8) & 0xff),
		byte((sum >> 16) & 0xff),
		byte(sum >> 24)})
}

func (c *Compiler) Next() {
	r, _, err := c.Reader.ReadRune()
	if err != nil {
		panic("Error reading next character")
	}
	c.Curr = r
}

func main() {
	data, err := syscall.Mmap(-1, 0, 4096, syscall.PROT_READ|syscall.PROT_WRITE|syscall.PROT_EXEC, syscall.MAP_PRIVATE|syscall.MAP_ANONYMOUS)
	if err != nil {
		fmt.Printf("Error: mmap: %s\n", err);
	}

	c := NewCompiler(os.Stdin)
	c.Program()
	copy(data, c.Buffer.Bytes())
	rv := C.callGate(unsafe.Pointer(&data[0]))
	fmt.Printf("==> %d\n", rv)
}