On 2/21/20 1:25 AM, 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, which is an another bug. > 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). > > Not only for the arm target, Philippe has also encountered this on MIPS. > Probably gdb has different assumption for different architectures. > > 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> > Tested-by: Philippe Mathieu-Daudé <phi...@redhat.com>
Reviewed-by: Luc Michel <luc.mic...@greensocs.com> > > --- > v2: polish commit message. > --- > gdbstub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/gdbstub.c b/gdbstub.c > index ce304ff482..adccd938e2 100644 > --- a/gdbstub.c > +++ b/gdbstub.c > @@ -2111,7 +2111,7 @@ static void handle_query_supported(GdbCmdContext > *gdb_ctx, void *user_ctx) > gdb_ctx->s->multiprocess = true; > } > > - pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf), ";multiprocess+"); > + pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf), > ";vContSupported+;multiprocess+"); > put_packet(gdb_ctx->s, gdb_ctx->str_buf); > } > >
