Issue using GDB for non-stop multi-core debugging.

[Rejeesh S. Babu]

Hi All,

We are using GDB 7.5 (via MI protocol) to debug a remote multi-core target in 
non-stop mode. We use custom GDB Server and GDB thread packets are interpreted 
as hardware core for multi-core debugging.

Everything is working fine except that step over through a piece of code which 
is simultaneously accessed by both cores is failing.

The failing scenario can be explained as below:

1. Core 0 is halted and core 1 is running before single stepping
2. When user single step core 0, GDB puts a BP in next location and run the 
target
3. Since core 1 is also executing this piece of code, core 1 takes this BP (GDB 
expect core 0 to take BP)
4. Our custom GDB Server sends the stop notification packet of core 1 
5. Irrespective of the fact that notification packet of core 1 was send, GDB 
tries to read register/memory values of core0 (which is running)
6. GDB Server respond with error packet and GDB stops functioning

Packets exchanged between GDB and GDB Server for single step :

Sending packet: $m80009000,4#5e...Ack
Packet received: 0800e003
Sending packet: $m80009000,4#5e...Ack
Packet received: 0800e003
Sending packet: $qTStatus#49...Ack
Packet received: 
Sending packet: $m80009000,4#5e...Ack
Packet received: 0800e003
Sending packet: $m80009000,4#5e...Ack
Packet received: 0800e003
Sending packet: $Z0,8000b024,4#d6...Ack
Packet received: OK
Packet Z0 (software-breakpoint) is supported
Sending packet: $vCont;c:1#13...Ack //GDB run core 1
Packet received: OK
  Notification received: Stop:T05thread:02; //Core 2 is halted 
stop notification captured
Sending packet: $vStopped#55...Ack
Packet received: OK
Sending packet: $Hg2#e1...Ack
Packet received: OK
Sending packet: $g#67...Ack
Packet received: 
00000000008b0010e08f0080020000000800c7cf424cfb231a0000001a00000000000000000000001a000000000062cfb81962cfa412b97f00ca9a3b00004800020000006476bc800000bc80accdbb800000bc808722c73b4337c3336322cf1f00000000d0300577081fc7cf081fc7cf0000c7cf081fc7cf032387bd24b00080018b00107cf82198d64f000094c40e770000800024b00080
Sending packet: $Hg1#e0...Ack //Though Core 2 was halted, GDB is requesting for 
Core 1 details
Packet received: E 00
Sending packet: $g#67...Ack
Packet received: 
00000000008b0010e08f0080020000000800c7cf424cfb231a0000001a00000000000000000000001a000000000062cfb81962cfa412b97f00ca9a3b00004800020000006476bc800000bc80accdbb800000bc808722c73b4337c3336322cf1f00000000d0300577081fc7cf081fc7cf0000c7cf081fc7cf032387bd24b00080018b00107cf82198d64f000094c40e770000800024b00080
Target is executing.


Is there a way to overcome this limitation? Is there any commands in GDB to 
handle such scenarios? Or is there any GDB patch? Or is it because something is 
missing in our custom GDB Server?

Any hint to help us progress is highly appreciated.

Thanking in anticipation,
Rejeesh
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