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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 armasm
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"strings"
)
// Plan9Syntax returns the Go assembler syntax for the instruction.
// The syntax was originally defined by Plan 9.
// The pc is the program counter of the instruction, used for expanding
// PC-relative addresses into absolute ones.
// The symname function queries the symbol table for the program
// being disassembled. Given a target address it returns the name and base
// address of the symbol containing the target, if any; otherwise it returns "", 0.
// The reader r should read from the text segment using text addresses
// as offsets; it is used to display pc-relative loads as constant loads.
func Plan9Syntax(inst Inst, pc uint64, symname func(uint64) (string, uint64), text io.ReaderAt) string {
if symname == nil {
symname = func(uint64) (string, uint64) { return "", 0 }
}
var args []string
for _, a := range inst.Args {
if a == nil {
break
}
args = append(args, plan9Arg(&inst, pc, symname, a))
}
op := inst.Op.String()
switch inst.Op &^ 15 {
case LDR_EQ, LDRB_EQ, LDRH_EQ:
// Check for RET
reg, _ := inst.Args[0].(Reg)
mem, _ := inst.Args[1].(Mem)
if inst.Op&^15 == LDR_EQ && reg == R15 && mem.Base == SP && mem.Sign == 0 && mem.Mode == AddrPostIndex {
return fmt.Sprintf("RET%s #%d", op[3:], mem.Offset)
}
// Check for PC-relative load.
if mem.Base == PC && mem.Sign == 0 && mem.Mode == AddrOffset && text != nil {
addr := uint32(pc) + 8 + uint32(mem.Offset)
buf := make([]byte, 4)
switch inst.Op &^ 15 {
case LDRB_EQ:
if _, err := text.ReadAt(buf[:1], int64(addr)); err != nil {
break
}
args[1] = fmt.Sprintf("$%#x", buf[0])
case LDRH_EQ:
if _, err := text.ReadAt(buf[:2], int64(addr)); err != nil {
break
}
args[1] = fmt.Sprintf("$%#x", binary.LittleEndian.Uint16(buf))
case LDR_EQ:
if _, err := text.ReadAt(buf, int64(addr)); err != nil {
break
}
x := binary.LittleEndian.Uint32(buf)
if s, base := symname(uint64(x)); s != "" && uint64(x) == base {
args[1] = fmt.Sprintf("$%s(SB)", s)
} else {
args[1] = fmt.Sprintf("$%#x", x)
}
}
}
}
// Move addressing mode into opcode suffix.
suffix := ""
switch inst.Op &^ 15 {
case LDR_EQ, LDRB_EQ, LDRH_EQ, STR_EQ, STRB_EQ, STRH_EQ:
mem, _ := inst.Args[1].(Mem)
switch mem.Mode {
case AddrOffset, AddrLDM:
// no suffix
case AddrPreIndex, AddrLDM_WB:
suffix = ".W"
case AddrPostIndex:
suffix = ".P"
}
off := ""
if mem.Offset != 0 {
off = fmt.Sprintf("%#x", mem.Offset)
}
base := fmt.Sprintf("(R%d)", int(mem.Base))
index := ""
if mem.Sign != 0 {
sign := ""
if mem.Sign < 0 {
sign = ""
}
shift := ""
if mem.Count != 0 {
shift = fmt.Sprintf("%s%d", plan9Shift[mem.Shift], mem.Count)
}
index = fmt.Sprintf("(%sR%d%s)", sign, int(mem.Index), shift)
}
args[1] = off + base + index
}
// Reverse args, placing dest last.
for i, j := 0, len(args)-1; i < j; i, j = i+1, j-1 {
args[i], args[j] = args[j], args[i]
}
switch inst.Op &^ 15 {
case MOV_EQ:
op = "MOVW" + op[3:]
case LDR_EQ:
op = "MOVW" + op[3:] + suffix
case LDRB_EQ:
op = "MOVB" + op[4:] + suffix
case LDRH_EQ:
op = "MOVH" + op[4:] + suffix
case STR_EQ:
op = "MOVW" + op[3:] + suffix
args[0], args[1] = args[1], args[0]
case STRB_EQ:
op = "MOVB" + op[4:] + suffix
args[0], args[1] = args[1], args[0]
case STRH_EQ:
op = "MOVH" + op[4:] + suffix
args[0], args[1] = args[1], args[0]
}
if args != nil {
op += " " + strings.Join(args, ", ")
}
return op
}
// assembler syntax for the various shifts.
// @x> is a lie; the assembler uses @> 0
// instead of @x> 1, but i wanted to be clear that it
// was a different operation (rotate right extended, not rotate right).
var plan9Shift = []string{"<<", ">>", "->", "@>", "@x>"}
func plan9Arg(inst *Inst, pc uint64, symname func(uint64) (string, uint64), arg Arg) string {
switch a := arg.(type) {
case Endian:
case Imm:
return fmt.Sprintf("$%d", int(a))
case Mem:
case PCRel:
addr := uint32(pc) + 8 + uint32(a)
if s, base := symname(uint64(addr)); s != "" && uint64(addr) == base {
return fmt.Sprintf("%s(SB)", s)
}
return fmt.Sprintf("%#x", addr)
case Reg:
if a < 16 {
return fmt.Sprintf("R%d", int(a))
}
case RegList:
var buf bytes.Buffer
start := -2
end := -2
fmt.Fprintf(&buf, "[")
flush := func() {
if start >= 0 {
if buf.Len() > 1 {
fmt.Fprintf(&buf, ",")
}
if start == end {
fmt.Fprintf(&buf, "R%d", start)
} else {
fmt.Fprintf(&buf, "R%d-R%d", start, end)
}
}
}
for i := 0; i < 16; i++ {
if a&(1<<uint(i)) != 0 {
if i == end+1 {
end++
continue
}
start = i
end = i
}
}
flush()
fmt.Fprintf(&buf, "]")
return buf.String()
case RegShift:
return fmt.Sprintf("R%d%s$%d", int(a.Reg), plan9Shift[a.Shift], int(a.Count))
case RegShiftReg:
return fmt.Sprintf("R%d%sR%d", int(a.Reg), plan9Shift[a.Shift], int(a.RegCount))
}
return strings.ToUpper(arg.String())
}
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