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package nguh
import (
"bytes"
"fmt"
"io"
"github.com/eaburns/peggy/peg"
"github.com/go-interpreter/wagon/wasm/leb128"
)
// Section is a WebAssembly binary section.
type Section struct {
Kind uint32
Len uint32
Data bytes.Buffer
}
// WebAssembly section types
const (
SectionTypeType = 0x01
SectionTypeImport = 0x02
SectionTypeFunc = 0x03
SectionTypeExport = 0x07
SectionTypeCode = 0x0a
)
// Commit turns a section into WebAssembly bytecode
func (s *Section) Commit(out io.Writer) error {
if s.Len != uint32(s.Data.Len()) {
s.Len = uint32(s.Data.Len())
}
if _, err := leb128.WriteVarUint32(out, s.Kind); err != nil {
return err
}
if _, err := leb128.WriteVarUint32(out, s.Len); err != nil {
return err
}
if _, err := io.Copy(out, &s.Data); err != nil {
return err
}
return nil
}
const (
ExportFunc = 0x60
WASMi32Type = 0x7f
)
func Compile(tree *peg.Node) ([]byte, error) {
out := bytes.NewBuffer([]byte{
// WebAssembly binary header / magic numbers
0x00, 0x61, 0x73, 0x6d, // \0asm wasm magic number
0x01, 0x00, 0x00, 0x00, // version 1
})
typeS := &Section{Kind: SectionTypeType}
typeS.Data.Write([]byte{
0x02, // 2 entries
ExportFunc, 0x01, WASMi32Type, 0x00, // function type 0, 1 i32 param, 0 return
ExportFunc, 0x00, 0x00, // function type 1, 0 param, 0 return
})
if err := typeS.Commit(out); err != nil {
return nil, fmt.Errorf("can't write type section: %v", err)
}
importS := &Section{Kind: SectionTypeImport}
importS.Data.Write([]byte{
0x01, // 1 entry
0x01, 0x68, // module h
0x01, 0x68, // name h
0x00, // type index
0x00, // function number
})
if err := importS.Commit(out); err != nil {
return nil, fmt.Errorf("can't write import section: %v", err)
}
funcS := &Section{Kind: SectionTypeFunc}
funcS.Data.Write([]byte{
0x01, // function 1
0x01, // type 1
})
if err := funcS.Commit(out); err != nil {
return nil, fmt.Errorf("can't write func section: %v", err)
}
exportS := &Section{Kind: SectionTypeExport}
exportS.Data.Write([]byte{
0x01, // 1 entry
0x01, 0x68, // "h"
0x00, 0x01, // function 1
})
if err := exportS.Commit(out); err != nil {
return nil, fmt.Errorf("can't write export section: %v", err)
}
codeS := &Section{Kind: SectionTypeCode}
codeS.Data.Write([]byte{
0x01, // 1 entry
})
funcBuf := bytes.NewBuffer([]byte{
0x01, // 1 local declaration
0x03, 0x7f, // 3 i32 values - (local i32 i32 i32)
0x41, 0x0a, // i32.const 10 '\n'
0x21, 0x00, // local.set 0
0x41, 0xe8, 0x00, // i32.const 104 - 'h'
0x21, 0x01, // local.set 1
0x41, 0x27, // i32.const 39 '
0x21, 0x02, // local.set 2
})
// compile AST to wasm
if len(tree.Kids) == 0 {
if err := compileOneNode(funcBuf, tree); err != nil {
return nil, err
}
} else {
for _, node := range tree.Kids {
if err := compileOneNode(funcBuf, node); err != nil {
return nil, err
}
}
}
// finally print newline
funcBuf.Write([]byte{
0x20, 0x00, // local.get 0
0x10, 0x00, // call 0
0x01, 0x01, // two padding NOPs to get a single `h` binary to be 69 bytes.
0x0b, // end of function
})
if _, err := leb128.WriteVarUint32(&codeS.Data, uint32(funcBuf.Len())); err != nil {
return nil, err
}
if _, err := io.Copy(&codeS.Data, funcBuf); err != nil {
return nil, err
}
if err := codeS.Commit(out); err != nil {
return nil, fmt.Errorf("can't write code section: %v", err)
}
return out.Bytes(), nil
}
func compileOneNode(out io.Writer, node *peg.Node) error {
switch node.Text {
case "h":
if _, err := out.Write([]byte{
0x20, 0x01, // local.get 1
0x10, 0x00, // call 0
}); err != nil {
return err
}
case "'":
if _, err := out.Write([]byte{
0x20, 0x02, // local.get 2
0x10, 0x00, // call 0
}); err != nil {
return err
}
default:
fmt.Errorf("h: le vi lerfu zo %q cu gentoldra", node.Text)
}
return nil
}
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