gdbstub: Introduce gdbserver_fork_start()

The upcoming follow-fork-mode child support requires knowing when
fork() is about to happen in order to initialize its state. Add a hook
for that.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240219141628.246823-5-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240305121005.3528075-6-alex.bennee@linaro.org>

bsd-user/main.c

@@ -113,6 +113,7 @@ void fork_start(void)
     start_exclusive();
     cpu_list_lock();
     mmap_fork_start();
+    gdbserver_fork_start();
 }
 
 void fork_end(int child)

gdbstub/user.c

@@ -356,6 +356,10 @@ int gdbserver_start(const char *port_or_path)
     return -1;
 }
 
+void gdbserver_fork_start(void)
+{
+}
+
 static void disable_gdbstub(CPUState *thread_cpu)
 {
     CPUState *cpu;

include/gdbstub/user.h

@@ -45,6 +45,11 @@ static inline int gdb_handlesig(CPUState *cpu, int sig)
  */
 void gdb_signalled(CPUArchState *as, int sig);
 
+/**
+ * gdbserver_fork_start() - inform gdb of the upcoming fork()
+ */
+void gdbserver_fork_start(void);
+
 /**
  * gdbserver_fork() - disable gdb stub for child processes.
  * @cs: CPU

linux-user/main.c

@@ -145,6 +145,7 @@ void fork_start(void)
     mmap_fork_start();
     cpu_list_lock();
     qemu_plugin_user_prefork_lock();
+    gdbserver_fork_start();
 }
 
 void fork_end(int child)