gasm-sdk/debug/disasm_linux_amd64.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

//go:build linux && amd64

package debug

import (
	"fmt"
	"strings"

	"sourcedock.dev/petrbalvin/gasm-sdk/arch"
	"sourcedock.dev/petrbalvin/gasm-sdk/disasm"
)

// Disassemble decodes the instruction at the given address in the debuggee's
// memory and returns its text representation and length in bytes.  An amd64
// instruction is up to 15 bytes long, but the read must not reach past the
// end of the mapping: when the full 15-byte window crosses into unmapped
// memory the window shrinks, because an instruction at the mapping's end is
// by construction no longer than the readable bytes that hold it.
func (s *Session) Disassemble(addr uint64) (string, int, error) {
	var lastErr error
	for _, n := range []int{15, 8, 4, 2, 1} {
		mem, err := s.ReadMemory(addr, n)
		if err != nil {
			lastErr = err
			continue
		}
		ins, derr := disasm.Decode(arch.AMD64, mem, addr)
		if derr != nil {
			return "", 0, derr
		}
		return ins.Text, ins.Len, nil
	}
	return "", 0, lastErr
}

// DisassembleN decodes up to n instructions starting at addr and returns
// them as a formatted string with addresses and byte offsets.
func (s *Session) DisassembleN(addr uint64, n int) string {
	var result strings.Builder
	pc := addr
	for range n {
		text, length, err := s.Disassemble(pc)
		if err != nil {
			result.WriteString(fmt.Sprintf("  %#08x: <error: %v>\n", pc, err))
			break
		}
		result.WriteString(fmt.Sprintf("  %#08x: %s\n", pc, text))
		if length == 0 {
			length = 1
		}
		pc += uint64(length)
	}
	return result.String()
}

// isCallInsn reports whether disassembled text (x86asm.IntelSyntax) is a
// call.  The first token must match exactly: a prefix test would also catch
// unrelated mnemonics.
func isCallInsn(text string) bool {
	m, _, _ := strings.Cut(text, " ")
	return strings.ToLower(m) == "call"
}