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[Bug 1907210] Re: QEMU gdbstub command "?" issue

From: Launchpad Bug Tracker
Subject: [Bug 1907210] Re: QEMU gdbstub command "?" issue
Date: Sat, 10 Jul 2021 04:17:37 -0000

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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  QEMU gdbstub command "?" issue

Status in QEMU:

Bug description:
  I am using some third party GDB client, and I have noticed that every time 
"?" command is send from the client, QEMU gdbstub removes all break points. 
This behaviour is not expected since "?" command should only return stop reason.
  Here is documentation from official gdb:
  ‘?’ Indicate the reason the target halted. The reply is the same as for step 
  continue. This packet has a special interpretation when the target is in 
  mode; see Section E.10 [Remote Non-Stop], page 733.
  Reply: See Section E.3 [Stop Reply Packets], page 693, for the reply 

  With some help on the irc, we have been able to pin point the failure 
point(in attachement file gdbstub.c).
  Function that handles "?" command has this comment in it:
       * Remove all the breakpoints when this query is issued,
       * because gdb is doing an initial connect and the state
       * should be cleaned up.
  From which it is clear that developer that wrote that code assumed, that 
because most popular gdb client only uses "?" command at initial connect, it is 
safe to also remove all BPs.
  In my opinion initial connect should be detected in some other way, and not 
with "?" command.
  Also note that official gdbserver does not remove the BPs when this command 
is send, this issue is present in QEMU and apparently also on kgdb(I was told 
that on irc, have not tested it myself)

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