[Qemu-devel] [PATCH 1/2] Add GDB qAttached support

[Fabien Chouteau]

With this patch QEMU handles qAttached request from gdb. When QEMU
replies 1, GDB sends a "detach" command at the end of a debugging
session otherwise GDB sends "kill".

The default value for qAttached is 1 on system emulation and 0 on user
emulation.

We introduce a new command line option. It's a generic option to
customize the gdb server:

-gdb-opts [attached=on|off]

The only parameter for now is "attached".

This patch implements the requirement described in Jan Kiszka's patch:
"gdbstub: Do not kill target in system emulation mode". The patch can
therefore be reverted.

Signed-off-by: Fabien Chouteau <address@hidden>
---
 gdbstub.c              |   38 +++++++++++++++++++++++++++++++++++++-
 include/exec/gdbstub.h |    2 ++
 qemu-options.hx        |   17 +++++++++++++++++
 vl.c                   |    3 +++
 4 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/gdbstub.c b/gdbstub.c
index e414ad9..de95849 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -32,7 +32,6 @@
 #include "monitor/monitor.h"
 #include "char/char.h"
 #include "sysemu/sysemu.h"
-#include "exec/gdbstub.h"
 #endif
 
 #define MAX_PACKET_LENGTH 4096
@@ -41,6 +40,13 @@
 #include "qemu/sockets.h"
 #include "sysemu/kvm.h"
 #include "qemu/bitops.h"
+#include "exec/gdbstub.h"
+
+#ifdef CONFIG_USER_ONLY
+static bool gdb_attached; /* false */
+#else
+static bool gdb_attached = true;
+#endif
 
 #ifndef TARGET_CPU_MEMORY_RW_DEBUG
 static inline int target_memory_rw_debug(CPUArchState *env, target_ulong addr,
@@ -2491,6 +2497,10 @@ static int gdb_handle_packet(GDBState *s, const char 
*line_buf)
             break;
         }
 #endif
+        if (strncmp(p, "Attached", 8) == 0) {
+            put_packet(s, gdb_attached ? "1" : "0");
+            break;
+        }
         /* Unrecognised 'q' command.  */
         goto unknown_command;
 
@@ -3055,3 +3065,29 @@ int gdbserver_start(const char *device)
     return 0;
 }
 #endif
+
+static QemuOptsList qemu_gdb_opts = {
+    .name = "gdb",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_gdb_opts.head),
+    .desc = {
+        {
+            .name = "attached",
+            .type = QEMU_OPT_BOOL,
+        },
+        { /* end of list */ }
+    },
+};
+
+void gdb_set_opts(const char *opts_str)
+{
+    QemuOpts *opts;
+
+    opts = qemu_opts_parse(&qemu_gdb_opts, opts_str, 0);
+    if (!opts) {
+        exit(1);
+    }
+
+    gdb_attached = qemu_opt_get_bool(opts, "attached", gdb_attached);
+
+    qemu_opts_del(opts);
+}
diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
index ba20afa..86fc18b 100644
--- a/include/exec/gdbstub.h
+++ b/include/exec/gdbstub.h
@@ -50,4 +50,6 @@ int gdbserver_start(const char *port);
 /* in gdbstub-xml.c, generated by scripts/feature_to_c.sh */
 extern const char *const xml_builtin[][2];
 
+void gdb_set_opts(const char *opts_str);
+
 #endif
diff --git a/qemu-options.hx b/qemu-options.hx
index cd76f2a..49a480f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2505,6 +2505,23 @@ within gdb and establish the connection via a pipe:
 @end example
 ETEXI
 
+DEF("gdb-opts", HAS_ARG, QEMU_OPTION_gdb_opts, \
+    "-gdb-opts attached=on|off\n"\
+    "                options for the gdb remote server\n", QEMU_ARCH_ALL)
+STEXI
address@hidden -gdb-opts @var{dev}
address@hidden -gdb-opts
+Set options for the gdb remote server:
address@hidden @option
address@hidden attached=on|off:
+
+When 'on' (default), gdb sends a 'detach' command at the end of debugging
+session, otherwise gdb sends a 'kill' command.
+
address@hidden table
+
+ETEXI
+
 DEF("s", 0, QEMU_OPTION_s, \
     "-s              shorthand for -gdb tcp::" DEFAULT_GDBSTUB_PORT "\n",
     QEMU_ARCH_ALL)
diff --git a/vl.c b/vl.c
index 154f7ba..cce96b6 100644
--- a/vl.c
+++ b/vl.c
@@ -3251,6 +3251,9 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_gdb:
                 add_device_config(DEV_GDB, optarg);
                 break;
+            case QEMU_OPTION_gdb_opts:
+                gdb_set_opts(optarg);
+                break;
             case QEMU_OPTION_L:
                 data_dir = optarg;
                 break;
-- 
1.7.9.5