Issues With Thread Events In User Mode GDBServer

[Simon Marchi]

On 2022-09-09 16:04, Bill Messmer via Gdb wrote:
> Folks,
> 
> Apologies if this is the wrong mailing list to ask a question regarding GDBServer / RSP and a potential bug.
> 
> I have been working on new extensibility API surfaces for the Windows platform debuggers that allow folks to write plug-ins that can connect those debugging tools to a variety of new targets including ones that are not Windows based.  We've had the ability to do this for post-mortem targets for some time and are, of late, working to expand that API surface to various forms of live targets.
> 
> As proof of concept for the API surface, I've been experimenting with writing such a plug-in to connect to the standard user mode GDBServer for Linux.  A few things I'll note:
> 
> 
>   1.  When thread events are enabled on the server via a QThreadEvents:1, GDBServer immediately crashes on any thread exit in "resume" on a NULL deref of current_thread.
> 
> 
> 
>   1.  I tried a quick patch here (adding "cs.last_status.kind() != TARGET_WAITKIND_THREAD_EXITED") to the set of conditions that won't set "current_thread->last_status" and the wXXX thread exit packets get sent; however, regardless of whether the target is in non-stop mode or not, the process is STILL RUNNING at the time the server sends the "wXXX" packet.
> 
> 
> Am I missing something with GDBServer and thread events or is this just not well supported...?  The process seems to be stopped at the point that a thread creation event gets sent...  but not for a thread exit...  I assume that's a bug somewhere in GDBServer...?  Or am I misreading the docs at https://sourceware.org/gdb/onlinedocs/gdb/General-Query-Packets.html...?  Is there some alternate means by which thread create/exit notifications come...?
> 
> Sincerely,
> 
> Bill Messmer
> wmessmer@microsoft.com<mailto:wmessmer@microsoft.com>

Hi Bill,

I don't quite understand the situation you are describing.  Can you
maybe send a log of the communication between your tool and GDBserver?

Simon