gdbstub: Introduce gdb_handle_set_thread_user()

The upcoming follow-fork-mode child support needs to perform certain
actions when GDB switches between the stopped parent and the stopped
child. Introduce a user-specific hook for this.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240219141628.246823-10-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240305121005.3528075-11-alex.bennee@linaro.org>

gdbstub/gdbstub.c

@@ -1099,6 +1099,7 @@ static void handle_cont_with_sig(GArray *params, void *user_ctx)
 
 static void handle_set_thread(GArray *params, void *user_ctx)
 {
+    uint32_t pid, tid;
     CPUState *cpu;
 
     if (params->len != 2) {
@@ -1116,8 +1117,14 @@ static void handle_set_thread(GArray *params, void *user_ctx)
         return;
     }
 
-    cpu = gdb_get_cpu(get_param(params, 1)->thread_id.pid,
-                      get_param(params, 1)->thread_id.tid);
+    pid = get_param(params, 1)->thread_id.pid;
+    tid = get_param(params, 1)->thread_id.tid;
+#ifdef CONFIG_USER_ONLY
+    if (gdb_handle_set_thread_user(pid, tid)) {
+        return;
+    }
+#endif
+    cpu = gdb_get_cpu(pid, tid);
     if (!cpu) {
         gdb_put_packet("E22");
         return;

gdbstub/internals.h

@@ -197,6 +197,7 @@ void gdb_handle_v_file_readlink(GArray *params, void *user_ctx); /* user */
 void gdb_handle_query_xfer_exec_file(GArray *params, void *user_ctx); /* user */
 void gdb_handle_set_catch_syscalls(GArray *params, void *user_ctx); /* user */
 void gdb_handle_query_supported_user(const char *gdb_supported); /* user */
+bool gdb_handle_set_thread_user(uint32_t pid, uint32_t tid); /* user */
 
 void gdb_handle_query_attached(GArray *params, void *user_ctx); /* both */
 

gdbstub/user.c

@@ -386,6 +386,11 @@ void gdb_handle_query_supported_user(const char *gdb_supported)
 {
 }
 
+bool gdb_handle_set_thread_user(uint32_t pid, uint32_t tid)
+{
+    return false;
+}
+
 /*
  * Execution state helpers
  */