warning: garbage in qC reply

warning: garbage in qC reply

[Mathieu Tarral]

Hi,

I'm writing a new GDB stub in Python, and while implementing
each command that is sent to me by the GDB client during
the attach phase, I'm facing an issue with the qC command:

GDB is asking me to set the current thread-id to -1, with Hc-1
and immediately after it query the current thread id, with qC
I return -1 with QC-1, and I get a warning:

Sending packet: $Hc-1#09...Ack
Packet received: OK
Sending packet: $qC#b4...Ack
Packet received: QC-1
warning: garbage in qC reply

Is -1 an invalid thread-id syntax for qC ?

Thanks !
--
Mathieu Tarral

Sent with ProtonMail Secure Email.

Re: warning: garbage in qC reply

[Emiliano Testa]

Hi Mathieu,
GDB is asking you to apply the next continue or step command to all threads
when it sends Hc-1:

from:
https://sourceware.org/gdb/onlinedocs/gdb/Packets.html#thread_002did-syntax

"Several packets and replies include a thread-id field to identify a
thread. Normally these are positive numbers with a target-specific
interpretation, formatted as big-endian hex strings. A thread-id can also
be a literal ‘-1’ to indicate all threads, or ‘0’ to pick any thread. "

So when receiving the Qc command your stub should reply with the currently
selected thread id, not -1.

Hope this helps

Emiliano



On Mon, 19 Nov 2018 at 16:34, Mathieu Tarral <mathieu.tarral@protonmail.com>
wrote:

> Hi,
>
> I'm writing a new GDB stub in Python, and while implementing
> each command that is sent to me by the GDB client during
> the attach phase, I'm facing an issue with the qC command:
>
> GDB is asking me to set the current thread-id to -1, with Hc-1
> and immediately after it query the current thread id, with qC
> I return -1 with QC-1, and I get a warning:
>
> Sending packet: $Hc-1#09...Ack
> Packet received: OK
> Sending packet: $qC#b4...Ack
> Packet received: QC-1
> warning: garbage in qC reply
>
> Is -1 an invalid thread-id syntax for qC ?
>
> Thanks !
> --
> Mathieu Tarral
>
> Sent with ProtonMail Secure Email.
>
>
>

-- 
Emiliano Testa
Undo software engineer

22 Station Road
Cambridge
CB1 2JD
United Kingdom