On 2/20/20 7:06 PM, Laurent Vivier wrote:
Le 20/02/2020 à 18:47, Philippe Mathieu-Daudé a écrit :
On 2/20/20 4:58 PM, Changbin Du wrote:
Recently when debugging an arm32 system on qemu, I found sometimes the
single-step command (stepi) is not working. This can be reproduced by
below steps:
1) start qemu-system-arm -s -S .. and wait for gdb connection.
2) start gdb and connect to qemu. In my case, gdb gets a wrong value
(0x60) for PC.
3) After connected, type 'stepi' and expect it will stop at next ins.
But, it has never stopped. This because:
1) We doesn't report ‘vContSupported’ feature to gdb explicitly and gdb
think we do not support it. In this case, gdb use a software
breakpoint
to emulate single-step.
2) Since gdb gets a wrong initial value of PC, then gdb inserts a
breakpoint to wrong place (PC+4).
Since we do support ‘vContSupported’ query command, so let's tell gdb
that
we support it.
Before this change, gdb send below 'Z0' packet to implement single-step:
gdb_handle_packet: Z0,4,4
After this change, gdb send "vCont;s.." which is expected:
gdb_handle_packet: vCont?
put_packet: vCont;c;C;s;S
gdb_handle_packet: vCont;s:p1.1;c:p1.-1
You actually fixed this for all architectures :)
This has been annoying me on MIPS since more than a year...
The problem started with an update of QEMU or of GDB?
At one point it seemed to work, so what happened?
I'd say gdb. I can try different combinations of QEMU/gdb but I won't do
that soon.
