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[PATCH v1 28/28] gdbstub: Fix single-step issue by confirming 'vContSupp
From: |
Alex Bennée |
Subject: |
[PATCH v1 28/28] gdbstub: Fix single-step issue by confirming 'vContSupported+' feature to gdb |
Date: |
Mon, 16 Mar 2020 17:21:55 +0000 |
From: Changbin Du <address@hidden>
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 <address@hidden>
Tested-by: Philippe Mathieu-Daudé <address@hidden>
Message-Id: <address@hidden>
[AJB: fix for static gdbstub]
Signed-off-by: Alex Bennée <address@hidden>
Reviewed-by: Luc Michel <address@hidden>
---
gdbstub.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/gdbstub.c b/gdbstub.c
index 9ae148cd1ff..013fb1ac0f1 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();
}
--
2.20.1
- [PATCH v1 27/28] gdbstub: do not split gdb_monitor_write payload, (continued)
- [PATCH v1 27/28] gdbstub: do not split gdb_monitor_write payload, Alex Bennée, 2020/03/16
- [PATCH v1 11/28] target/arm: use gdb_get_reg helpers, Alex Bennée, 2020/03/16
- [PATCH v1 09/28] gdbstub: move mem_buf to GDBState and use GByteArray, Alex Bennée, 2020/03/16
- [PATCH v1 12/28] target/m68k: use gdb_get_reg helpers, Alex Bennée, 2020/03/16
- [PATCH v1 07/28] gdbstub: stop passing GDBState * around and use global, Alex Bennée, 2020/03/16
- [PATCH v1 13/28] target/i386: use gdb_get_reg helpers, Alex Bennée, 2020/03/16
- [PATCH v1 15/28] target/arm: prepare for multiple dynamic XMLs, Alex Bennée, 2020/03/16
- [PATCH v1 28/28] gdbstub: Fix single-step issue by confirming 'vContSupported+' feature to gdb,
Alex Bennée <=
- [PATCH v1 14/28] gdbstub: extend GByteArray to read register helpers, Alex Bennée, 2020/03/16
- [PATCH v1 24/28] tests/tcg/aarch64: add SVE iotcl test, Alex Bennée, 2020/03/16
- Re: [PATCH v1 24/28] tests/tcg/aarch64: add SVE iotcl test, Aleksandar Markovic, 2020/03/17
[PATCH v1 17/28] target/arm: default SVE length to 64 bytes for linux-user, Alex Bennée, 2020/03/16
[PATCH v1 22/28] tests/guest-debug: add a simple test runner, Alex Bennée, 2020/03/16