[Bug 1907210] [NEW] QEMU gdbstub command "?" issue

[Matic Kres]

Public bug reported:

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 and
continue. This packet has a special interpretation when the target is in 
non-stop
mode; see Section E.10 [Remote Non-Stop], page 733.
Reply: See Section E.3 [Stop Reply Packets], page 693, for the reply 
specifications.

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)

** Affects: qemu
     Importance: Undecided
         Status: New

** Attachment added: "qemuissue.jpg"
   
https://bugs.launchpad.net/bugs/1907210/+attachment/5441925/+files/qemuissue.jpg

** Description changed:

  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 
and
  continue. This packet has a special interpretation when the target is in 
non-stop
  mode; see Section E.10 [Remote Non-Stop], page 733.
  Reply: See Section E.3 [Stop Reply Packets], page 693, for the reply 
specifications.
  
  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. 
+     /*
+      * 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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https://bugs.launchpad.net/bugs/1907210

Title:
  QEMU gdbstub command "?" issue

Status in QEMU:
  New

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 
and
  continue. This packet has a special interpretation when the target is in 
non-stop
  mode; see Section E.10 [Remote Non-Stop], page 733.
  Reply: See Section E.3 [Stop Reply Packets], page 693, for the reply 
specifications.

  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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