func TestReadWrite(t *testing.T) {
	// Test that we get the same data in a write-read roundtrip.

	// Write a symbol, a relocation, and an aux info.
	var buf bytes.Buffer
	w := dummyWriter(&buf)

	var s Sym
	s.SetABI(1)
	s.SetType(uint8(objabi.STEXT))
	s.SetFlag(0x12)
	s.SetSiz(12345)
	s.SetAlign(8)
	s.Write(w)

	var r Reloc
	r.SetOff(12)
	r.SetSiz(4)
	r.SetType(uint16(objabi.R_ADDR))
	r.SetAdd(54321)

	case ABI0:
		hash = ctxt.hash
	case ABIInternal:
		hash = ctxt.funchash
	default:
		panic("unknown ABI")
	}

	ctxt.hashmu.Lock()
	s := hash[name]
	if s == nil {
		s = &LSym{Name: name}
		s.SetABI(abi)
		hash[name] = s
		if init != nil {
			init(s)
		}
	}
	ctxt.hashmu.Unlock()
	return s
}

// Lookup looks up the symbol with name name.
// If it does not exist, it creates it.

			v &^= flag
		}
		if atomic.CompareAndSwapUint32((*uint32)(a), uint32(v0), uint32(v)) {
			break
		}
	}
}

func (a *Attribute) ABI() ABI { return ABI(a.load() / attrABIBase) }
func (a *Attribute) SetABI(abi ABI) {
	const mask = 1 // Only one ABI bit for now.
	for {
		v0 := a.load()
		v := (v0 &^ (mask * attrABIBase)) | Attribute(abi)*attrABIBase
		if atomic.CompareAndSwapUint32((*uint32)(a), uint32(v0), uint32(v)) {

			default:
				align = 1
			}
		}
	}
	if s.Size > cutoff {
		w.ctxt.Diag("%s: symbol too large (%d bytes > %d bytes)", s.Name, s.Size, cutoff)
	}
	o := &w.tmpSym
	o.SetName(name, w.Writer)
	o.SetABI(abi)
	o.SetType(uint8(s.Type))
	o.SetFlag(flag)
	o.SetFlag2(flag2)
	o.SetSiz(uint32(s.Size))
	o.SetAlign(align)
	o.Write(w.Writer)
}

func (w *writer) Hash64(s *LSym) {

func (s *Sym) SetName(x string, w *Writer) {
	binary.LittleEndian.PutUint32(s[:], uint32(len(x)))
	binary.LittleEndian.PutUint32(s[4:], w.stringOff(x))
}

func (s *Sym) SetABI(x uint16)   { binary.LittleEndian.PutUint16(s[8:], x) }
func (s *Sym) SetType(x uint8)   { s[10] = x }
func (s *Sym) SetFlag(x uint8)   { s[11] = x }
func (s *Sym) SetFlag2(x uint8)  { s[12] = x }