code review 153750044: cmd/objdump: move armasm, x86asm into internal packages

src/cmd/internal/rsc.io/arm/armasm/decode.go

Index: src/cmd/internal/rsc.io/arm/armasm/decode.go
===================================================================
new file mode 100644
--- /dev/null
+++ b/src/cmd/internal/rsc.io/arm/armasm/decode.go
@@ -0,0 +1,567 @@
+// 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 armasm
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+// An instFormat describes the format of an instruction encoding.
+// An instruction with 32-bit value x matches the format if x&mask == value
+// and the condition matches.
+// The condition matches if x>>28 == 0xF && value>>28==0xF
+// or if x>>28 != 0xF and value>>28 == 0.
+// If x matches the format, then the rest of the fields describe how to interpret x.
+// The opBits describe bits that should be extracted from x and added to the opcode.
+// For example opBits = 0x1234 means that the value
+//	(2 bits at offset 1) followed by (4 bits at offset 3)
+// should be added to op.
+// Finally the args describe how to decode the instruction arguments.
+// args is stored as a fixed-size array; if there are fewer than len(args) arguments,
+// args[i] == 0 marks the end of the argument list.
+type instFormat struct {
+	mask     uint32
+	value    uint32
+	priority int8
+	op       Op
+	opBits   uint64
+	args     instArgs
+}
+
+type instArgs [4]instArg
+
+var (
+	errMode    = fmt.Errorf("unsupported execution mode")
+	errShort   = fmt.Errorf("truncated instruction")
+	errUnknown = fmt.Errorf("unknown instruction")
+)
+
+var decoderCover []bool
+
+// Decode decodes the leading bytes in src as a single instruction.
+func Decode(src []byte, mode Mode) (inst Inst, err error) {
+	if mode != ModeARM {
+		return Inst{}, errMode
+	}
+	if len(src) < 4 {
+		return Inst{}, errShort
+	}
+
+	if decoderCover == nil {
+		decoderCover = make([]bool, len(instFormats))
+	}
+
+	x := binary.LittleEndian.Uint32(src)
+
+	// The instFormat table contains both conditional and unconditional instructions.
+	// Considering only the top 4 bits, the conditional instructions use mask=0, value=0,
+	// while the unconditional instructions use mask=f, value=f.
+	// Prepare a version of x with the condition cleared to 0 in conditional instructions
+	// and then assume mask=f during matching.
+	const condMask = 0xf0000000
+	xNoCond := x
+	if x&condMask != condMask {
+		xNoCond &^= condMask
+	}
+	var priority int8
+Search:
+	for i := range instFormats {
+		f := &instFormats[i]
+		if xNoCond&(f.mask|condMask) != f.value || f.priority <= priority {
+			continue
+		}
+		delta := uint32(0)
+		deltaShift := uint(0)
+		for opBits := f.opBits; opBits != 0; opBits >>= 16 {
+			n := uint(opBits & 0xFF)
+			off := uint((opBits >> 8) & 0xFF)
+			delta |= (x >> off) & (1<<n - 1) << deltaShift
+			deltaShift += n
+		}
+		op := f.op + Op(delta)
+
+		// Special case: BKPT encodes with condition but cannot have one.
+		if op&^15 == BKPT_EQ && op != BKPT {
+			continue Search
+		}
+
+		var args Args
+		for j, aop := range f.args {
+			if aop == 0 {
+				break
+			}
+			arg := decodeArg(aop, x)
+			if arg == nil { // cannot decode argument
+				continue Search
+			}
+			args[j] = arg
+		}
+
+		decoderCover[i] = true
+
+		inst = Inst{
+			Op:   op,
+			Args: args,
+			Enc:  x,
+			Len:  4,
+		}
+		priority = f.priority
+		continue Search
+	}
+	if inst.Op != 0 {
+		return inst, nil
+	}
+	return Inst{}, errUnknown
+}
+
+// An instArg describes the encoding of a single argument.
+// In the names used for arguments, _p_ means +, _m_ means -,
+// _pm_ means ± (usually keyed by the U bit).
+// The _W suffix indicates a general addressing mode based on the P and W bits.
+// The _offset and _postindex suffixes force the given addressing mode.
+// The rest should be somewhat self-explanatory, at least given
+// the decodeArg function.
+type instArg uint8
+
+const (
+	_ instArg = iota
+	arg_APSR
+	arg_FPSCR
+	arg_Dn_half
+	arg_R1_0
+	arg_R1_12
+	arg_R2_0
+	arg_R2_12
+	arg_R_0
+	arg_R_12
+	arg_R_12_nzcv
+	arg_R_16
+	arg_R_16_WB
+	arg_R_8
+	arg_R_rotate
+	arg_R_shift_R
+	arg_R_shift_imm
+	arg_SP
+	arg_Sd
+	arg_Sd_Dd
+	arg_Dd_Sd
+	arg_Sm
+	arg_Sm_Dm
+	arg_Sn
+	arg_Sn_Dn
+	arg_const
+	arg_endian
+	arg_fbits
+	arg_fp_0
+	arg_imm24
+	arg_imm5
+	arg_imm5_32
+	arg_imm5_nz
+	arg_imm_12at8_4at0
+	arg_imm_4at16_12at0
+	arg_imm_vfp
+	arg_label24
+	arg_label24H
+	arg_label_m_12
+	arg_label_p_12
+	arg_label_pm_12
+	arg_label_pm_4_4
+	arg_lsb_width
+	arg_mem_R
+	arg_mem_R_pm_R_W
+	arg_mem_R_pm_R_postindex
+	arg_mem_R_pm_R_shift_imm_W
+	arg_mem_R_pm_R_shift_imm_offset
+	arg_mem_R_pm_R_shift_imm_postindex
+	arg_mem_R_pm_imm12_W
+	arg_mem_R_pm_imm12_offset
+	arg_mem_R_pm_imm12_postindex
+	arg_mem_R_pm_imm8_W
+	arg_mem_R_pm_imm8_postindex
+	arg_mem_R_pm_imm8at0_offset
+	arg_option
+	arg_registers
+	arg_registers1
+	arg_registers2
+	arg_satimm4
+	arg_satimm5
+	arg_satimm4m1
+	arg_satimm5m1
+	arg_widthm1
+)
+
+// decodeArg decodes the arg described by aop from the instruction bits x.
+// It returns nil if x cannot be decoded according to aop.
+func decodeArg(aop instArg, x uint32) Arg {
+	switch aop {
+	default:
+		return nil
+
+	case arg_APSR:
+		return APSR
+	case arg_FPSCR:
+		return FPSCR
+
+	case arg_R_0:
+		return Reg(x & (1<<4 - 1))
+	case arg_R_8:
+		return Reg((x >> 8) & (1<<4 - 1))
+	case arg_R_12:
+		return Reg((x >> 12) & (1<<4 - 1))
+	case arg_R_16:
+		return Reg((x >> 16) & (1<<4 - 1))
+
+	case arg_R_12_nzcv:
+		r := Reg((x >> 12) & (1<<4 - 1))
+		if r == R15 {
+			return APSR_nzcv
+		}
+		return r
+
+	case arg_R_16_WB:
+		mode := AddrLDM
+		if (x>>21)&1 != 0 {
+			mode = AddrLDM_WB
+		}
+		return Mem{Base: Reg((x >> 16) & (1<<4 - 1)), Mode: mode}
+
+	case arg_R_rotate:
+		Rm := Reg(x & (1<<4 - 1))
+		typ, count := decodeShift(x)
+		// ROR #0 here means ROR #0, but decodeShift rewrites to RRX #1.
+		if typ == RotateRightExt {
+			return Reg(Rm)
+		}
+		return RegShift{Rm, typ, uint8(count)}
+
+	case arg_R_shift_R:
+		Rm := Reg(x & (1<<4 - 1))
+		Rs := Reg((x >> 8) & (1<<4 - 1))
+		typ := Shift((x >> 5) & (1<<2 - 1))
+		return RegShiftReg{Rm, typ, Rs}
+
+	case arg_R_shift_imm:
+		Rm := Reg(x & (1<<4 - 1))
+		typ, count := decodeShift(x)
+		if typ == ShiftLeft && count == 0 {
+			return Reg(Rm)
+		}
+		return RegShift{Rm, typ, uint8(count)}
+
+	case arg_R1_0:
+		return Reg((x & (1<<4 - 1)))
+	case arg_R1_12:
+		return Reg(((x >> 12) & (1<<4 - 1)))
+	case arg_R2_0:
+		return Reg((x & (1<<4 - 1)) | 1)
+	case arg_R2_12:
+		return Reg(((x >> 12) & (1<<4 - 1)) | 1)
+
+	case arg_SP:
+		return SP
+
+	case arg_Sd_Dd:
+		v := (x >> 12) & (1<<4 - 1)
+		vx := (x >> 22) & 1
+		sz := (x >> 8) & 1
+		if sz != 0 {
+			return D0 + Reg(vx<<4+v)
+		} else {
+			return S0 + Reg(v<<1+vx)
+		}
+
+	case arg_Dd_Sd:
+		return decodeArg(arg_Sd_Dd, x^(1<<8))
+
+	case arg_Sd:
+		v := (x >> 12) & (1<<4 - 1)
+		vx := (x >> 22) & 1
+		return S0 + Reg(v<<1+vx)
+
+	case arg_Sm_Dm:
+		v := (x >> 0) & (1<<4 - 1)
+		vx := (x >> 5) & 1
+		sz := (x >> 8) & 1
+		if sz != 0 {
+			return D0 + Reg(vx<<4+v)
+		} else {
+			return S0 + Reg(v<<1+vx)
+		}
+
+	case arg_Sm:
+		v := (x >> 0) & (1<<4 - 1)
+		vx := (x >> 5) & 1
+		return S0 + Reg(v<<1+vx)
+
+	case arg_Dn_half:
+		v := (x >> 16) & (1<<4 - 1)
+		vx := (x >> 7) & 1
+		return RegX{D0 + Reg(vx<<4+v), int((x >> 21) & 1)}
+
+	case arg_Sn_Dn:
+		v := (x >> 16) & (1<<4 - 1)
+		vx := (x >> 7) & 1
+		sz := (x >> 8) & 1
+		if sz != 0 {
+			return D0 + Reg(vx<<4+v)
+		} else {
+			return S0 + Reg(v<<1+vx)
+		}
+
+	case arg_Sn:
+		v := (x >> 16) & (1<<4 - 1)
+		vx := (x >> 7) & 1
+		return S0 + Reg(v<<1+vx)
+
+	case arg_const:
+		v := x & (1<<8 - 1)
+		rot := (x >> 8) & (1<<4 - 1) * 2
+		if rot > 0 && v&3 == 0 {
+			// could rotate less
+			return ImmAlt{uint8(v), uint8(rot)}
+		}
+		if rot >= 24 && ((v<<(32-rot))&0xFF)>>(32-rot) == v {
+			// could wrap around to rot==0.
+			return ImmAlt{uint8(v), uint8(rot)}
+		}
+		return Imm(v>>rot | v<<(32-rot))
+
+	case arg_endian:
+		return Endian((x >> 9) & 1)
+
+	case arg_fbits:
+		return Imm((16 << ((x >> 7) & 1)) - ((x&(1<<4-1))<<1 | (x>>5)&1))
+
+	case arg_fp_0:
+		return Imm(0)
+
+	case arg_imm24:
+		return Imm(x & (1<<24 - 1))
+
+	case arg_imm5:
+		return Imm((x >> 7) & (1<<5 - 1))
+
+	case arg_imm5_32:
+		x = (x >> 7) & (1<<5 - 1)
+		if x == 0 {
+			x = 32
+		}
+		return Imm(x)
+
+	case arg_imm5_nz:
+		x = (x >> 7) & (1<<5 - 1)
+		if x == 0 {
+			return nil
+		}
+		return Imm(x)
+
+	case arg_imm_4at16_12at0:
+		return Imm((x>>16)&(1<<4-1)<<12 | x&(1<<12-1))
+
+	case arg_imm_12at8_4at0:
+		return Imm((x>>8)&(1<<12-1)<<4 | x&(1<<4-1))
+
+	case arg_imm_vfp:
+		x = (x>>16)&(1<<4-1)<<4 | x&(1<<4-1)
+		return Imm(x)
+
+	case arg_label24:
+		imm := (x & (1<<24 - 1)) << 2
+		return PCRel(int32(imm<<6) >> 6)
+
+	case arg_label24H:
+		h := (x >> 24) & 1
+		imm := (x&(1<<24-1))<<2 | h<<1
+		return PCRel(int32(imm<<6) >> 6)
+
+	case arg_label_m_12:
+		d := int32(x & (1<<12 - 1))
+		return Mem{Base: PC, Mode: AddrOffset, Offset: int16(-d)}
+
+	case arg_label_p_12:
+		d := int32(x & (1<<12 - 1))
+		return Mem{Base: PC, Mode: AddrOffset, Offset: int16(d)}
+
+	case arg_label_pm_12:
+		d := int32(x & (1<<12 - 1))
+		u := (x >> 23) & 1
+		if u == 0 {
+			d = -d
+		}
+		return Mem{Base: PC, Mode: AddrOffset, Offset: int16(d)}
+
+	case arg_label_pm_4_4:
+		d := int32((x>>8)&(1<<4-1)<<4 | x&(1<<4-1))
+		u := (x >> 23) & 1
+		if u == 0 {
+			d = -d
+		}
+		return PCRel(d)
+
+	case arg_lsb_width:
+		lsb := (x >> 7) & (1<<5 - 1)
+		msb := (x >> 16) & (1<<5 - 1)
+		if msb < lsb || msb >= 32 {
+			return nil
+		}
+		return Imm(msb + 1 - lsb)
+
+	case arg_mem_R:
+		Rn := Reg((x >> 16) & (1<<4 - 1))
+		return Mem{Base: Rn, Mode: AddrOffset}
+
+	case arg_mem_R_pm_R_postindex:
+		// Treat [<Rn>],+/-<Rm> like [<Rn>,+/-<Rm>{,<shift>}]{!}
+		// by forcing shift bits to <<0 and P=0, W=0 (postindex=true).
+		return decodeArg(arg_mem_R_pm_R_shift_imm_W, x&^((1<<7-1)<<5|1<<24|1<<21))
+
+	case arg_mem_R_pm_R_W:
+		// Treat [<Rn>,+/-<Rm>]{!} like [<Rn>,+/-<Rm>{,<shift>}]{!}
+		// by forcing shift bits to <<0.
+		return decodeArg(arg_mem_R_pm_R_shift_imm_W, x&^((1<<7-1)<<5))
+
+	case arg_mem_R_pm_R_shift_imm_offset:
+		// Treat [<Rn>],+/-<Rm>{,<shift>} like [<Rn>,+/-<Rm>{,<shift>}]{!}
+		// by forcing P=1, W=0 (index=false, wback=false).
+		return decodeArg(arg_mem_R_pm_R_shift_imm_W, x&^(1<<21)|1<<24)
+
+	case arg_mem_R_pm_R_shift_imm_postindex:
+		// Treat [<Rn>],+/-<Rm>{,<shift>} like [<Rn>,+/-<Rm>{,<shift>}]{!}
+		// by forcing P=0, W=0 (postindex=true).
+		return decodeArg(arg_mem_R_pm_R_shift_imm_W, x&^(1<<24|1<<21))
+
+	case arg_mem_R_pm_R_shift_imm_W:
+		Rn := Reg((x >> 16) & (1<<4 - 1))
+		Rm := Reg(x & (1<<4 - 1))
+		typ, count := decodeShift(x)
+		u := (x >> 23) & 1
+		w := (x >> 21) & 1
+		p := (x >> 24) & 1
+		if p == 0 && w == 1 {
+			return nil
+		}
+		sign := int8(+1)
+		if u == 0 {
+			sign = -1
+		}
+		mode := AddrMode(uint8(p<<1) | uint8(w^1))
+		return Mem{Base: Rn, Mode: mode, Sign: sign, Index: Rm, Shift: typ, Count: count}
+
+	case arg_mem_R_pm_imm12_offset:
+		// Treat [<Rn>,#+/-<imm12>] like [<Rn>{,#+/-<imm12>}]{!}
+		// by forcing P=1, W=0 (index=false, wback=false).
+		return decodeArg(arg_mem_R_pm_imm12_W, x&^(1<<21)|1<<24)
+
+	case arg_mem_R_pm_imm12_postindex:
+		// Treat [<Rn>],#+/-<imm12> like [<Rn>{,#+/-<imm12>}]{!}
+		// by forcing P=0, W=0 (postindex=true).
+		return decodeArg(arg_mem_R_pm_imm12_W, x&^(1<<24|1<<21))
+
+	case arg_mem_R_pm_imm12_W:
+		Rn := Reg((x >> 16) & (1<<4 - 1))
+		u := (x >> 23) & 1
+		w := (x >> 21) & 1
+		p := (x >> 24) & 1
+		if p == 0 && w == 1 {
+			return nil
+		}
+		sign := int8(+1)
+		if u == 0 {
+			sign = -1
+		}
+		imm := int16(x & (1<<12 - 1))
+		mode := AddrMode(uint8(p<<1) | uint8(w^1))
+		return Mem{Base: Rn, Mode: mode, Offset: int16(sign) * imm}
+
+	case arg_mem_R_pm_imm8_postindex:
+		// Treat [<Rn>],#+/-<imm8> like [<Rn>{,#+/-<imm8>}]{!}
+		// by forcing P=0, W=0 (postindex=true).
+		return decodeArg(arg_mem_R_pm_imm8_W, x&^(1<<24|1<<21))
+
+	case arg_mem_R_pm_imm8_W:
+		Rn := Reg((x >> 16) & (1<<4 - 1))
+		u := (x >> 23) & 1
+		w := (x >> 21) & 1
+		p := (x >> 24) & 1
+		if p == 0 && w == 1 {
+			return nil
+		}
+		sign := int8(+1)
+		if u == 0 {
+			sign = -1
+		}
+		imm := int16((x>>8)&(1<<4-1)<<4 | x&(1<<4-1))
+		mode := AddrMode(uint8(p<<1) | uint8(w^1))
+		return Mem{Base: Rn, Mode: mode, Offset: int16(sign) * imm}
+
+	case arg_mem_R_pm_imm8at0_offset:
+		Rn := Reg((x >> 16) & (1<<4 - 1))
+		u := (x >> 23) & 1
+		sign := int8(+1)
+		if u == 0 {
+			sign = -1
+		}
+		imm := int16(x&(1<<8-1)) << 2
+		return Mem{Base: Rn, Mode: AddrOffset, Offset: int16(sign) * imm}
+
+	case arg_option:
+		return Imm(x & (1<<4 - 1))
+
+	case arg_registers:
+		return RegList(x & (1<<16 - 1))
+
+	case arg_registers2:
+		x &= 1<<16 - 1
+		n := 0
+		for i := 0; i < 16; i++ {
+			if x>>uint(i)&1 != 0 {
+				n++
+			}
+		}
+		if n < 2 {
+			return nil
+		}
+		return RegList(x)
+
+	case arg_registers1:
+		Rt := (x >> 12) & (1<<4 - 1)
+		return RegList(1 << Rt)
+
+	case arg_satimm4:
+		return Imm((x >> 16) & (1<<4 - 1))
+
+	case arg_satimm5:
+		return Imm((x >> 16) & (1<<5 - 1))
+
+	case arg_satimm4m1:
+		return Imm((x>>16)&(1<<4-1) + 1)
+
+	case arg_satimm5m1:
+		return Imm((x>>16)&(1<<5-1) + 1)
+
+	case arg_widthm1:
+		return Imm((x>>16)&(1<<5-1) + 1)
+
+	}
+}
+
+// decodeShift decodes the shift-by-immediate encoded in x.
+func decodeShift(x uint32) (Shift, uint8) {
+	count := (x >> 7) & (1<<5 - 1)
+	typ := Shift((x >> 5) & (1<<2 - 1))
+	switch typ {
+	case ShiftRight, ShiftRightSigned:
+		if count == 0 {
+			count = 32
+		}
+	case RotateRight:
+		if count == 0 {
+			typ = RotateRightExt
+			count = 1
+		}
+	}
+	return typ, uint8(count)
+}