path: root/core/asm/compiler.go

// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package asm

import (
    "fmt"
    "math/big"
    "os"
    "strings"

    "github.com/dexon-foundation/dexon/common/math"
    "github.com/dexon-foundation/dexon/core/vm"
)

// Compiler contains information about the parsed source
// and holds the tokens for the program.
type Compiler struct {
    tokens []token
    binary []interface{}

    labels map[string]int

    pc, pos int

    debug bool
}

// newCompiler returns a new allocated compiler.
func NewCompiler(debug bool) *Compiler {
    return &Compiler{
        labels: make(map[string]int),
        debug:  debug,
    }
}

// Feed feeds tokens in to ch and are interpreted by
// the compiler.
//
// feed is the first pass in the compile stage as it
// collects the used labels in the program and keeps a
// program counter which is used to determine the locations
// of the jump dests. The labels can than be used in the
// second stage to push labels and determine the right
// position.
func (c *Compiler) Feed(ch <-chan token) {
    for i := range ch {
        switch i.typ {
        case number:
            num := math.MustParseBig256(i.text).Bytes()
            if len(num) == 0 {
                num = []byte{0}
            }
            c.pc += len(num)
        case stringValue:
            c.pc += len(i.text) - 2
        case element:
            c.pc++
        case labelDef:
            c.labels[i.text] = c.pc
            c.pc++
        case label:
            c.pc += 5
        }

        c.tokens = append(c.tokens, i)
    }
    if c.debug {
        fmt.Fprintln(os.Stderr, "found", len(c.labels), "labels")
    }
}

// Compile compiles the current tokens and returns a
// binary string that can be interpreted by the EVM
// and an error if it failed.
//
// compile is the second stage in the compile phase
// which compiles the tokens to EVM instructions.
func (c *Compiler) Compile() (string, []error) {
    var errors []error
    // continue looping over the tokens until
    // the stack has been exhausted.
    for c.pos < len(c.tokens) {
        if err := c.compileLine(); err != nil {
            errors = append(errors, err)
        }
    }

    // turn the binary to hex
    var bin string
    for _, v := range c.binary {
        switch v := v.(type) {
        case vm.OpCode:
            bin += fmt.Sprintf("%x", []byte{byte(v)})
        case []byte:
            bin += fmt.Sprintf("%x", v)
        }
    }
    return bin, errors
}

// next returns the next token and increments the
// position.
func (c *Compiler) next() token {
    token := c.tokens[c.pos]
    c.pos++
    return token
}

// compileLine compiles a single line instruction e.g.
// "push 1", "jump @label".
func (c *Compiler) compileLine() error {
    n := c.next()
    if n.typ != lineStart {
        return compileErr(n, n.typ.String(), lineStart.String())
    }

    lvalue := c.next()
    switch lvalue.typ {
    case eof:
        return nil
    case element:
        if err := c.compileElement(lvalue); err != nil {
            return err
        }
    case labelDef:
        c.compileLabel()
    case lineEnd:
        return nil
    default:
        return compileErr(lvalue, lvalue.text, fmt.Sprintf("%v or %v", labelDef, element))
    }

    if n := c.next(); n.typ != lineEnd {
        return compileErr(n, n.text, lineEnd.String())
    }

    return nil
}

// compileNumber compiles the number to bytes
func (c *Compiler) compileNumber(element token) (int, error) {
    num := math.MustParseBig256(element.text).Bytes()
    if len(num) == 0 {
        num = []byte{0}
    }
    c.pushBin(num)
    return len(num), nil
}

// compileElement compiles the element (push & label or both)
// to a binary representation and may error if incorrect statements
// where fed.
func (c *Compiler) compileElement(element token) error {
    // check for a jump. jumps must be read and compiled
    // from right to left.
    if isJump(element.text) {
        rvalue := c.next()
        switch rvalue.typ {
        case number:
            // TODO figure out how to return the error properly
            c.compileNumber(rvalue)
        case stringValue:
            // strings are quoted, remove them.
            c.pushBin(rvalue.text[1 : len(rvalue.text)-2])
        case label:
            c.pushBin(vm.PUSH4)
            pos := big.NewInt(int64(c.labels[rvalue.text])).Bytes()
            pos = append(make([]byte, 4-len(pos)), pos...)
            c.pushBin(pos)
        default:
            return compileErr(rvalue, rvalue.text, "number, string or label")
        }
        // push the operation
        c.pushBin(toBinary(element.text))
        return nil
    } else if isPush(element.text) {
        // handle pushes. pushes are read from left to right.
        var value []byte

        rvalue := c.next()
        switch rvalue.typ {
        case number:
            value = math.MustParseBig256(rvalue.text).Bytes()
            if len(value) == 0 {
                value = []byte{0}
            }
        case stringValue:
            value = []byte(rvalue.text[1 : len(rvalue.text)-1])
        case label:
            value = make([]byte, 4)
            copy(value, big.NewInt(int64(c.labels[rvalue.text])).Bytes())
        default:
            return compileErr(rvalue, rvalue.text, "number, string or label")
        }

        if len(value) > 32 {
            return fmt.Errorf("%d type error: unsupported string or number with size > 32", rvalue.lineno)
        }

        c.pushBin(vm.OpCode(int(vm.PUSH1) - 1 + len(value)))
        c.pushBin(value)
    } else {
        c.pushBin(toBinary(element.text))
    }

    return nil
}

// compileLabel pushes a jumpdest to the binary slice.
func (c *Compiler) compileLabel() {
    c.pushBin(vm.JUMPDEST)
}

// pushBin pushes the value v to the binary stack.
func (c *Compiler) pushBin(v interface{}) {
    if c.debug {
        fmt.Printf("%d: %v\n", len(c.binary), v)
    }
    c.binary = append(c.binary, v)
}

// isPush returns whether the string op is either any of
// push(N).
func isPush(op string) bool {
    return strings.ToUpper(op) == "PUSH"
}

// isJump returns whether the string op is jump(i)
func isJump(op string) bool {
    return strings.ToUpper(op) == "JUMPI" || strings.ToUpper(op) == "JUMP"
}

// toBinary converts text to a vm.OpCode
func toBinary(text string) vm.OpCode {
    return vm.StringToOp(strings.ToUpper(text))
}

type compileError struct {
    got  string
    want string

    lineno int
}

func (err compileError) Error() string {
    return fmt.Sprintf("%d syntax error: unexpected %v, expected %v", err.lineno, err.got, err.want)
}

func compileErr(c token, got, want string) error {
    return compileError{
        got:    got,
        want:   want,
        lineno: c.lineno,
    }
}