Re: [PATCH] btrace: diagnose "record btrace pt" without libipt

[Pedro Alves <palves@redhat.com>]

On 11/20/2015 12:11 PM, Metzger, Markus T wrote:

> The record target is popped off the target stack on disconnect.  This disables
> branch tracing.  The below log is for BTS but the logic is the same for PT.
> 	Sending packet: $Qbtrace:off#37...Packet received: OK

> 
> After reconnecting, you need to enable btrace again.

I see.  But then it sounds like we'll have the problem if the connection
drops unexpectedly -- gdb won't be able to tell the server to
disable Qbtrace.  I guess the easiest way to emulate is kill gdb:

 #1 - enable btrace pt
 #2 - connection is terminated unexpectedly / kill gdb
 #3 - reconnect to gdbserver

a) Does the new gdb get out of sync and confused?

b) What if btrace pt was enabled on the inferior, and the gdb that
   reconnects in #3 above is compiled _without_ libipt?
   Will "info record" still crash?  What I'm thinking is that
   a similar format check may be necessary around this code path,
   not only at PT enable time.

Thanks,
Pedro Alves