What causes "must specify at least one argument for qRRCmd" in go-delve/delve?

Always pass at least one argument, e.g. conn.qRRCmd("checkpoints")

must specify at least one argument for qRRCmd

Error message

must specify at least one argument for qRRCmd

What it means

qRRCmd sends the 'qRRCmd' packet used to query/mutate mozilla rr state. It requires at least one argument because the packet format joins arguments with ':' after the command name; calling it with zero arguments would produce a malformed packet, so it panics instead.

Source

Thrown at pkg/proc/gdbserial/gdbserver_conn.go:1196

	return sp, nil
}

// restart executes a 'vRun' command.
func (conn *gdbConn) restart(pos string) error {
	conn.outbuf.Reset()
	fmt.Fprint(&conn.outbuf, "$vRun;")
	if pos != "" {
		fmt.Fprint(&conn.outbuf, ";")
		writeAsciiBytes(&conn.outbuf, []byte(pos))
	}
	_, err := conn.exec(conn.outbuf.Bytes(), "restart")
	return err
}

// qRRCmd executes a qRRCmd command
func (conn *gdbConn) qRRCmd(args ...string) (string, error) {
	if len(args) == 0 {
		panic("must specify at least one argument for qRRCmd")
	}
	conn.outbuf.Reset()
	fmt.Fprint(&conn.outbuf, "$qRRCmd")
	for i, arg := range args {
		fmt.Fprint(&conn.outbuf, ":")
		if i == 0 && (conn.newRRCmdStyle || conn.threadSuffixSupported) {
			// newer versions of RR require the command to be followed by a thread id
			// and the command name to be unescaped.
			fmt.Fprintf(&conn.outbuf, "%s:-1", arg)
		} else {
			writeAsciiBytes(&conn.outbuf, []byte(arg))
		}
	}
	resp, err := conn.exec(conn.outbuf.Bytes(), "qRRCmd")
	if err != nil {
		return "", err
	}
	data := make([]byte, 0, len(resp)/2)

View on GitHub (pinned to a23773e6c3)

Solutions

Always pass at least one argument, e.g. conn.qRRCmd("checkpoints")
Audit the call site that builds the args slice; guard against len(args)==0 before calling
If the command legitimately takes no args, send a different packet or a default argument supported by rr

Example fix

// before
conn.qRRCmd(args...)
// after
if len(args) == 0 {
    return "", errors.New("qRRCmd requires arguments")
}
conn.qRRCmd(args...)

Defensive patterns

Strategy: validation

Validate before calling

if len(args) == 0 {
    return errors.New("qRRCmd requires at least one argument")
}

Try / catch

defer func() {
    if r := recover(); r != nil { err = fmt.Errorf("qRRCmd: %v", r) }
}()

Prevention

Guard variadic arg slices before packet construction
Consult rr's qRRCmd documentation for valid argument forms
Add unit tests for packet builders with empty inputs

When it happens

Trigger: Calling conn.qRRCmd() with no variadic arguments from internal code (e.g. rr checkpoint/readPacket helpers built incorrectly).

Common situations: Custom rr integration code, patched forks of delve, or new features issuing qRRCmd queries with a dynamically built (and accidentally empty) argument list.

Related errors

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/4e167ffac2843e26. Report an issue: GitHub.