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authorChangbin Du <changbin.du@gmail.com>2020-03-16 17:21:55 +0000
committerAlex Bennée <alex.bennee@linaro.org>2020-03-17 17:38:52 +0000
commit3bc2609d478779be600fd66744eb4e3730ec5e33 (patch)
tree38227b92c327c2b5770c8d5e95efc3d63306116c
parentd86b4672f2ee4775ce5711c5626e6311efd788c8 (diff)
gdbstub: Fix single-step issue by confirming 'vContSupported+' feature to gdb
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.du@gmail.com> Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com> Message-Id: <20200221002559.6768-1-changbin.du@gmail.com> [AJB: fix for static gdbstub] Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Luc Michel <luc.michel@greensocs.com> Message-Id: <20200316172155.971-29-alex.bennee@linaro.org>
-rw-r--r--gdbstub.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/gdbstub.c b/gdbstub.c
index 9ae148cd1f..013fb1ac0f 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -2130,7 +2130,7 @@ static void handle_query_supported(GdbCmdContext *gdb_ctx, void *user_ctx)
gdbserver_state.multiprocess = true;
}
- g_string_append(gdbserver_state.str_buf, ";multiprocess+");
+ g_string_append(gdbserver_state.str_buf, ";vContSupported+;multiprocess+");
put_strbuf();
}