gdbstub: Introduce gdb_handle_query_supported_user()

The upcoming follow-fork-mode child support requires advertising the
fork-events feature, which is user-specific. Introduce a user-specific
hook for this.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240219141628.246823-9-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240305121005.3528075-10-alex.bennee@linaro.org>

gdbstub/gdbstub.c

@@ -1655,9 +1655,15 @@ static void handle_query_supported(GArray *params, void *user_ctx)
     g_string_append(gdbserver_state.str_buf, ";qXfer:exec-file:read+");
 #endif
 
-    if (params->len &&
-        strstr(get_param(params, 0)->data, "multiprocess+")) {
-        gdbserver_state.multiprocess = true;
+    if (params->len) {
+        const char *gdb_supported = get_param(params, 0)->data;
+
+        if (strstr(gdb_supported, "multiprocess+")) {
+            gdbserver_state.multiprocess = true;
+        }
+#if defined(CONFIG_USER_ONLY)
+        gdb_handle_query_supported_user(gdb_supported);
+#endif
     }
 
     g_string_append(gdbserver_state.str_buf, ";vContSupported+;multiprocess+");

gdbstub/internals.h

@@ -196,6 +196,7 @@ void gdb_handle_v_file_pread(GArray *params, void *user_ctx); /* user */
 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 */
 
 void gdb_handle_query_attached(GArray *params, void *user_ctx); /* both */
 

gdbstub/user.c

@@ -382,6 +382,10 @@ void gdbserver_fork_end(CPUState *cpu, pid_t pid)
     disable_gdbstub(cpu);
 }
 
+void gdb_handle_query_supported_user(const char *gdb_supported)
+{
+}
+
 /*
  * Execution state helpers
  */