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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ppc64asm
import (
"encoding/binary"
"fmt"
"log"
)
const debugDecode = false
// instFormat is a decoding rule for one specific instruction form.
// a uint32 instruction ins matches the rule if ins&Mask == Value
// DontCare bits should be zero, but the machine might not reject
// ones in those bits, they are mainly reserved for future expansion
// of the instruction set.
// The Args are stored in the same order as the instruction manual.
type instFormat struct {
Op Op
Mask uint32
Value uint32
DontCare uint32
Args [5]*argField
}
// argField indicate how to decode an argument to an instruction.
// First parse the value from the BitFields, shift it left by Shift
// bits to get the actual numerical value.
type argField struct {
Type ArgType
Shift uint8
BitFields
}
// Parse parses the Arg out from the given binary instruction i.
func (a argField) Parse(i uint32) Arg {
switch a.Type {
default:
return nil
case TypeUnknown:
return nil
case TypeReg:
return R0 + Reg(a.BitFields.Parse(i))
case TypeCondRegBit:
return Cond0LT + CondReg(a.BitFields.Parse(i))
case TypeCondRegField:
return CR0 + CondReg(a.BitFields.Parse(i))
case TypeFPReg:
return F0 + Reg(a.BitFields.Parse(i))
case TypeVecReg:
return V0 + Reg(a.BitFields.Parse(i))
case TypeVecSReg:
return VS0 + Reg(a.BitFields.Parse(i))
case TypeSpReg:
return SpReg(a.BitFields.Parse(i))
case TypeImmSigned:
return Imm(a.BitFields.ParseSigned(i) << a.Shift)
case TypeImmUnsigned:
return Imm(a.BitFields.Parse(i) << a.Shift)
case TypePCRel:
return PCRel(a.BitFields.ParseSigned(i) << a.Shift)
case TypeLabel:
return Label(a.BitFields.ParseSigned(i) << a.Shift)
case TypeOffset:
return Offset(a.BitFields.ParseSigned(i) << a.Shift)
}
}
type ArgType int8
const (
TypeUnknown ArgType = iota
TypePCRel // PC-relative address
TypeLabel // absolute address
TypeReg // integer register
TypeCondRegBit // conditional register bit (0-31)
TypeCondRegField // conditional register field (0-7)
TypeFPReg // floating point register
TypeVecReg // vector register
TypeVecSReg // VSX register
TypeSpReg // special register (depends on Op)
TypeImmSigned // signed immediate
TypeImmUnsigned // unsigned immediate/flag/mask, this is the catch-all type
TypeOffset // signed offset in load/store
TypeLast // must be the last one
)
func (t ArgType) String() string {
switch t {
default:
return fmt.Sprintf("ArgType(%d)", int(t))
case TypeUnknown:
return "Unknown"
case TypeReg:
return "Reg"
case TypeCondRegBit:
return "CondRegBit"
case TypeCondRegField:
return "CondRegField"
case TypeFPReg:
return "FPReg"
case TypeVecReg:
return "VecReg"
case TypeVecSReg:
return "VecSReg"
case TypeSpReg:
return "SpReg"
case TypeImmSigned:
return "ImmSigned"
case TypeImmUnsigned:
return "ImmUnsigned"
case TypePCRel:
return "PCRel"
case TypeLabel:
return "Label"
case TypeOffset:
return "Offset"
}
}
func (t ArgType) GoString() string {
s := t.String()
if t > 0 && t < TypeLast {
return "Type" + s
}
return s
}
var (
// Errors
errShort = fmt.Errorf("truncated instruction")
errUnknown = fmt.Errorf("unknown instruction")
)
var decoderCover []bool
// Decode decodes the leading bytes in src as a single instruction using
// byte order ord.
func Decode(src []byte, ord binary.ByteOrder) (inst Inst, err error) {
if len(src) < 4 {
return inst, errShort
}
if decoderCover == nil {
decoderCover = make([]bool, len(instFormats))
}
inst.Len = 4 // only 4-byte instructions are supported
ui := ord.Uint32(src[:inst.Len])
inst.Enc = ui
for i, iform := range instFormats {
if ui&iform.Mask != iform.Value {
continue
}
if ui&iform.DontCare != 0 {
if debugDecode {
log.Printf("Decode(%#x): unused bit is 1 for Op %s", ui, iform.Op)
}
// to match GNU objdump (libopcodes), we ignore don't care bits
}
for i, argfield := range iform.Args {
if argfield == nil {
break
}
inst.Args[i] = argfield.Parse(ui)
}
inst.Op = iform.Op
if debugDecode {
log.Printf("%#x: search entry %d", ui, i)
continue
}
break
}
if inst.Op == 0 {
return inst, errUnknown
}
return inst, nil
}
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