gdbstub: Call gdbserver_fork() both in parent and in child

The upcoming follow-fork-mode child support requires post-fork message
exchange between the parent and the child. Prepare gdbserver_fork() for
this purpose. Rename it to gdbserver_fork_end() to better reflect its
purpose.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240219141628.246823-8-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240305121005.3528075-9-alex.bennee@linaro.org>

bsd-user/main.c

@@ -138,10 +138,11 @@ void fork_end(pid_t pid)
          */
         qemu_init_cpu_list();
         get_task_state(thread_cpu)->ts_tid = qemu_get_thread_id();
-        gdbserver_fork(thread_cpu, pid);
+        gdbserver_fork_end(thread_cpu, pid);
     } else {
         mmap_fork_end(child);
         cpu_list_unlock();
+        gdbserver_fork_end(thread_cpu, pid);
         end_exclusive();
     }
 }

gdbstub/user.c

@@ -374,10 +374,9 @@ static void disable_gdbstub(CPUState *thread_cpu)
     tb_flush(thread_cpu);
 }
 
-/* Disable gdb stub for child processes.  */
-void gdbserver_fork(CPUState *cpu, pid_t pid)
+void gdbserver_fork_end(CPUState *cpu, pid_t pid)
 {
-    if (!gdbserver_state.init || gdbserver_user_state.fd < 0) {
+    if (pid != 0 || !gdbserver_state.init || gdbserver_user_state.fd < 0) {
         return;
     }
     disable_gdbstub(cpu);

include/gdbstub/user.h

@@ -51,10 +51,11 @@ void gdb_signalled(CPUArchState *as, int sig);
 void gdbserver_fork_start(void);
 
 /**
- * gdbserver_fork() - disable gdb stub for child processes.
+ * gdbserver_fork_end() - inform gdb of the completed fork()
  * @cs: CPU
+ * @pid: 0 if in child process, -1 if fork failed, child process pid otherwise
  */
-void gdbserver_fork(CPUState *cs, pid_t pid);
+void gdbserver_fork_end(CPUState *cs, pid_t pid);
 
 /**
  * gdb_syscall_entry() - inform gdb of syscall entry and yield control to it

linux-user/main.c

@@ -165,10 +165,10 @@ void fork_end(pid_t pid)
         }
         qemu_init_cpu_list();
         get_task_state(thread_cpu)->ts_tid = qemu_get_thread_id();
-        gdbserver_fork(thread_cpu, pid);
     } else {
         cpu_list_unlock();
     }
+    gdbserver_fork_end(thread_cpu, pid);
     /*
      * qemu_init_cpu_list() reinitialized the child exclusive state, but we
      * also need to keep current_cpu consistent, so call end_exclusive() for