On Thu, 20 Feb 2020 at 15:59, Changbin Du <changbin...@gmail.com> 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 > > Signed-off-by: Changbin Du <changbin...@gmail.com>
Certainly if we support vCont we should advertise it. But why does the fallback path not work? That is, why does gdb get a wrong PC value initially? thanks -- PMM
