96 lines
3.0 KiB
Go
96 lines
3.0 KiB
Go
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// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
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// SPDX-License-Identifier: BSD-3-Clause
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// Package disasm decodes machine code back to instruction text for the four
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// architectures gasm assembles. It is a thin, platform-independent wrapper
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// over golang.org/x/arch and backs both the `gasm dis` command and the live
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// debugger views.
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package disasm
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import (
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"fmt"
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"golang.org/x/arch/arm64/arm64asm"
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"golang.org/x/arch/loong64/loong64asm"
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"golang.org/x/arch/riscv64/riscv64asm"
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"golang.org/x/arch/x86/x86asm"
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"sourcedock.dev/petrbalvin/gasm-devkit/arch"
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)
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// Instruction is one decoded instruction: its text form, its length in bytes
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// and the address it was decoded at.
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type Instruction struct {
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Addr uint64
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Text string
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Len int
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}
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// Decode decodes the instruction at the start of code, located at addr.
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// code needs to hold at least the one instruction being decoded (amd64 may
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// consume up to 15 bytes). Undecodable bytes yield the placeholder text "???"
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// and a length of one word (four bytes, one on amd64) so that a listing can
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// keep making progress, mirroring the debugger's behaviour.
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func Decode(a arch.Arch, code []byte, addr uint64) (Instruction, error) {
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if len(code) == 0 {
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return Instruction{}, fmt.Errorf("disasm: empty input")
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}
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switch a {
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case arch.ARM64:
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if len(code) < 4 {
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return Instruction{}, fmt.Errorf("disasm: need 4 bytes, have %d", len(code))
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}
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inst, err := arm64asm.Decode(code)
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if err != nil {
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return Instruction{Addr: addr, Text: "???", Len: 4}, nil
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}
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return Instruction{Addr: addr, Text: arm64asm.GoSyntax(inst, addr, nil, nil), Len: 4}, nil
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case arch.RISCV:
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// The compressed extensions are decoded transparently; a 16-bit
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// instruction only needs its two bytes.
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inst, err := riscv64asm.Decode(code)
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if err != nil {
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return Instruction{Addr: addr, Text: "???", Len: 2}, nil
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}
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return Instruction{Addr: addr, Text: riscv64asm.GoSyntax(inst, addr, nil, nil), Len: inst.Len}, nil
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case arch.LOONG64:
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if len(code) < 4 {
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return Instruction{}, fmt.Errorf("disasm: need 4 bytes, have %d", len(code))
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}
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inst, err := loong64asm.Decode(code)
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if err != nil {
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return Instruction{Addr: addr, Text: "???", Len: 4}, nil
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}
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return Instruction{Addr: addr, Text: loong64asm.GoSyntax(inst, addr, nil), Len: 4}, nil
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default: // amd64
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inst, err := x86asm.Decode(code, 64)
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if err != nil {
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return Instruction{Addr: addr, Text: "???", Len: 1}, nil
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}
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return Instruction{Addr: addr, Text: x86asm.IntelSyntax(inst, addr, nil), Len: inst.Len}, nil
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}
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}
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// Block decodes up to max instructions from code starting at addr and returns
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// them in order. Decoding stops at the end of code or once an instruction
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// would run past it.
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func Block(a arch.Arch, code []byte, addr uint64, max int) []Instruction {
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var out []Instruction
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pc := 0
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for len(out) < max && pc < len(code) {
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ins, err := Decode(a, code[pc:], addr+uint64(pc))
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if err != nil {
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break
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}
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if ins.Len <= 0 || pc+ins.Len > len(code) {
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break
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}
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out = append(out, ins)
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pc += ins.Len
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}
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return out
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}
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