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From: Ilya Leoshkevich <iii@linux.ibm.com>
To: Warner Losh <imp@bsdimp.com>, Riku Voipio <riku.voipio@iki.fi>,
Laurent Vivier <laurent@vivier.eu>, Paolo Bonzini <pbonzini@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>
Cc: Kyle Evans <kevans@freebsd.org>,
=?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= <philmd@linaro.org>,
qemu-devel@nongnu.org, Ilya Leoshkevich <iii@linux.ibm.com>
Subject: [PATCH v3 6/8] gdbstub: Allow late attachment
Date: Mon, 16 Dec 2024 13:33:24 +0100
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Allow debugging individual processes in multi-process applications by
starting them with export QEMU_GDB=3D/tmp/qemu-%d.sock,suspend=3Dn.
Currently one would have to attach to every process to ensure the app
makes progress.
In case suspend=3Dn is not specified, the flow remains unchanged. If it
is specified, then accepting the client connection is delegated to a
thread. In the future this machinery may be reused for handling
reconnections and interruptions.
On accepting a connection, the thread schedules gdb_handlesig() on the
first CPU and wakes it up with host_interrupt_signal. Note that the
result of this gdb_handlesig() invocation is handled, as opposed to
many other existing call sites. These other call sites probably need to
be fixed separately.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
bsd-user/main.c | 1 -
gdbstub/user.c | 120 ++++++++++++++++++++++++++++++++++++++++++----
linux-user/main.c | 1 -
3 files changed, 110 insertions(+), 12 deletions(-)
diff --git a/bsd-user/main.c b/bsd-user/main.c
index 61ca73c4781..ca4773a3f40 100644
--- a/bsd-user/main.c
+++ b/bsd-user/main.c
@@ -628,7 +628,6 @@ int main(int argc, char **argv)
=20
if (gdbstub) {
gdbserver_start(gdbstub);
- gdb_handlesig(cpu, 0, NULL, NULL, 0);
}
cpu_loop(env);
/* never exits */
diff --git a/gdbstub/user.c b/gdbstub/user.c
index c900d0a52fe..6ada0d687b9 100644
--- a/gdbstub/user.c
+++ b/gdbstub/user.c
@@ -10,6 +10,7 @@
*/
=20
#include "qemu/osdep.h"
+#include <sys/syscall.h>
#include "qemu/bitops.h"
#include "qemu/cutils.h"
#include "qemu/sockets.h"
@@ -21,6 +22,7 @@
#include "gdbstub/user.h"
#include "gdbstub/enums.h"
#include "hw/core/cpu.h"
+#include "user/signal.h"
#include "trace.h"
#include "internals.h"
=20
@@ -416,11 +418,101 @@ static int gdbserver_open_port(int port)
return fd;
}
=20
-int gdbserver_start(const char *port_or_path)
+static bool gdbserver_accept(int port, int gdb_fd, const char *port_or_pat=
h)
{
- int port =3D g_ascii_strtoull(port_or_path, NULL, 10);
+ bool ret;
+
+ if (port > 0) {
+ ret =3D gdb_accept_tcp(gdb_fd);
+ } else {
+ ret =3D gdb_accept_socket(gdb_fd);
+ if (ret) {
+ gdbserver_user_state.socket_path =3D g_strdup(port_or_path);
+ }
+ }
+
+ if (!ret) {
+ close(gdb_fd);
+ }
+
+ return ret;
+}
+
+struct {
+ int port;
int gdb_fd;
+ char *port_or_path;
+} gdbserver_args;
+
+static void do_gdb_handlesig(CPUState *cs, run_on_cpu_data arg)
+{
+ int sig;
+
+ sig =3D target_to_host_signal(gdb_handlesig(cs, 0, NULL, NULL, 0));
+ if (sig >=3D 1 && sig < NSIG) {
+ qemu_kill_thread(gdb_get_cpu_index(cs), sig);
+ }
+}
+
+static void *gdbserver_accept_thread(void *arg)
+{
+ if (gdbserver_accept(gdbserver_args.port, gdbserver_args.gdb_fd,
+ gdbserver_args.port_or_path)) {
+ CPUState *cs =3D first_cpu;
+
+ async_safe_run_on_cpu(cs, do_gdb_handlesig, RUN_ON_CPU_NULL);
+ qemu_kill_thread(gdb_get_cpu_index(cs), host_interrupt_signal);
+ }
+
+ g_free(gdbserver_args.port_or_path);
+
+ return NULL;
+}
+
+__attribute__((__format__(__printf__, 1, 2)))
+static void print_usage(const char *format, ...)
+{
+ va_list ap;
+
+ va_start(ap, format);
+ vfprintf(stderr, format, ap);
+ va_end(ap);
+ fprintf(stderr, "Usage: -g {port|path}[,suspend=3D{y|n}]\n");
+}
+
+#define SUSPEND "suspend=3D"
+
+int gdbserver_start(const char *args)
+{
+ g_auto(GStrv) argv =3D g_strsplit(args, ",", 0);
+ const char *port_or_path =3D NULL;
+ bool suspend =3D true;
+ int gdb_fd, port;
+ GStrv arg;
=20
+ for (arg =3D argv; *arg; arg++) {
+ if (g_str_has_prefix(*arg, SUSPEND)) {
+ const char *val =3D *arg + strlen(SUSPEND);
+
+ suspend =3D (strcmp(val, "y") =3D=3D 0);
+ if (!suspend && (strcmp(val, "n") !=3D 0)) {
+ print_usage("Bad option value: %s", *arg);
+ return -1;
+ }
+ } else {
+ if (port_or_path) {
+ print_usage("Unknown option: %s", *arg);
+ return -1;
+ }
+ port_or_path =3D *arg;
+ }
+ }
+ if (!port_or_path) {
+ print_usage("Port or path not specified");
+ return -1;
+ }
+
+ port =3D g_ascii_strtoull(port_or_path, NULL, 10);
if (port > 0) {
gdb_fd =3D gdbserver_open_port(port);
} else {
@@ -431,16 +523,24 @@ int gdbserver_start(const char *port_or_path)
return -1;
}
=20
- if (port > 0 && gdb_accept_tcp(gdb_fd)) {
- return 0;
- } else if (gdb_accept_socket(gdb_fd)) {
- gdbserver_user_state.socket_path =3D g_strdup(port_or_path);
+ if (suspend) {
+ if (gdbserver_accept(port, gdb_fd, port_or_path)) {
+ gdb_handlesig(first_cpu, 0, NULL, NULL, 0);
+ return 0;
+ } else {
+ return -1;
+ }
+ } else {
+ QemuThread thread;
+
+ gdbserver_args.port =3D port;
+ gdbserver_args.gdb_fd =3D gdb_fd;
+ gdbserver_args.port_or_path =3D g_strdup(port_or_path);
+ qemu_thread_create(&thread, "gdb-accept",
+ &gdbserver_accept_thread, NULL,
+ QEMU_THREAD_DETACHED);
return 0;
}
-
- /* gone wrong */
- close(gdb_fd);
- return -1;
}
=20
void gdbserver_fork_start(void)
diff --git a/linux-user/main.c b/linux-user/main.c
index b09af8d4365..97245ab37c2 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -1027,7 +1027,6 @@ int main(int argc, char **argv, char **envp)
gdbstub);
exit(EXIT_FAILURE);
}
- gdb_handlesig(cpu, 0, NULL, NULL, 0);
}
=20
#ifdef CONFIG_SEMIHOSTING
--=20
2.47.0