gdbstub: reject unsupported flags in handle_set_qemu_sstep

handle_query_qemu_sstepbits is reporting NOIRQ and NOTIMER bits
even if they are not supported (as is the case with record/replay).
Instead, store the supported singlestep flags and reject
any unsupported bits in handle_set_qemu_sstep.  This removes
the need for the get_sstep_flags() wrapper.

While at it, move the variables in GDBState, instead of using
global variables.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
[Extracted from Maxim's patch into a separate commit. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20211111110604.207376-4-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

gdbstub.c

@@ -368,27 +368,10 @@ typedef struct GDBState {
     gdb_syscall_complete_cb current_syscall_cb;
     GString *str_buf;
     GByteArray *mem_buf;
+    int sstep_flags;
+    int supported_sstep_flags;
 } GDBState;
 
-/* By default use no IRQs and no timers while single stepping so as to
- * make single stepping like an ICE HW step.
- */
-static int sstep_flags = SSTEP_ENABLE|SSTEP_NOIRQ|SSTEP_NOTIMER;
-
-/* Retrieves flags for single step mode. */
-static int get_sstep_flags(void)
-{
-    /*
-     * In replay mode all events written into the log should be replayed.
-     * That is why NOIRQ flag is removed in this mode.
-     */
-    if (replay_mode != REPLAY_MODE_NONE) {
-        return SSTEP_ENABLE;
-    } else {
-        return sstep_flags;
-    }
-}
-
 static GDBState gdbserver_state;
 
 static void init_gdbserver_state(void)
@@ -399,6 +382,26 @@ static void init_gdbserver_state(void)
     gdbserver_state.str_buf = g_string_new(NULL);
     gdbserver_state.mem_buf = g_byte_array_sized_new(MAX_PACKET_LENGTH);
     gdbserver_state.last_packet = g_byte_array_sized_new(MAX_PACKET_LENGTH + 4);
+
+    /*
+     * In replay mode all events will come from the log and can't be
+     * suppressed otherwise we would break determinism. However as those
+     * events are tied to the number of executed instructions we won't see
+     * them occurring every time we single step.
+     */
+    if (replay_mode != REPLAY_MODE_NONE) {
+        gdbserver_state.supported_sstep_flags = SSTEP_ENABLE;
+    } else {
+        gdbserver_state.supported_sstep_flags =
+            SSTEP_ENABLE | SSTEP_NOIRQ | SSTEP_NOTIMER;
+    }
+
+    /*
+     * By default use no IRQs and no timers while single stepping so as to
+     * make single stepping like an ICE HW step.
+     */
+    gdbserver_state.sstep_flags = gdbserver_state.supported_sstep_flags;
+
 }
 
 #ifndef CONFIG_USER_ONLY
@@ -505,7 +508,7 @@ static int gdb_continue_partial(char *newstates)
     CPU_FOREACH(cpu) {
         if (newstates[cpu->cpu_index] == 's') {
             trace_gdbstub_op_stepping(cpu->cpu_index);
-            cpu_single_step(cpu, sstep_flags);
+            cpu_single_step(cpu, gdbserver_state.sstep_flags);
         }
     }
     gdbserver_state.running_state = 1;
@@ -524,7 +527,7 @@ static int gdb_continue_partial(char *newstates)
                 break; /* nothing to do here */
             case 's':
                 trace_gdbstub_op_stepping(cpu->cpu_index);
-                cpu_single_step(cpu, get_sstep_flags());
+                cpu_single_step(cpu, gdbserver_state.sstep_flags);
                 cpu_resume(cpu);
                 flag = 1;
                 break;
@@ -1883,7 +1886,7 @@ static void handle_step(GArray *params, void *user_ctx)
         gdb_set_cpu_pc((target_ulong)get_param(params, 0)->val_ull);
     }
 
-    cpu_single_step(gdbserver_state.c_cpu, get_sstep_flags());
+    cpu_single_step(gdbserver_state.c_cpu, gdbserver_state.sstep_flags);
     gdb_continue();
 }
 
@@ -2017,24 +2020,44 @@ static void handle_v_commands(GArray *params, void *user_ctx)
 
 static void handle_query_qemu_sstepbits(GArray *params, void *user_ctx)
 {
-    g_string_printf(gdbserver_state.str_buf, "ENABLE=%x,NOIRQ=%x,NOTIMER=%x",
-                    SSTEP_ENABLE, SSTEP_NOIRQ, SSTEP_NOTIMER);
+    g_string_printf(gdbserver_state.str_buf, "ENABLE=%x", SSTEP_ENABLE);
+
+    if (gdbserver_state.supported_sstep_flags & SSTEP_NOIRQ) {
+        g_string_append_printf(gdbserver_state.str_buf, ",NOIRQ=%x",
+                               SSTEP_NOIRQ);
+    }
+
+    if (gdbserver_state.supported_sstep_flags & SSTEP_NOTIMER) {
+        g_string_append_printf(gdbserver_state.str_buf, ",NOTIMER=%x",
+                               SSTEP_NOTIMER);
+    }
+
     put_strbuf();
 }
 
 static void handle_set_qemu_sstep(GArray *params, void *user_ctx)
 {
+    int new_sstep_flags;
+
     if (!params->len) {
         return;
     }
 
-    sstep_flags = get_param(params, 0)->val_ul;
+    new_sstep_flags = get_param(params, 0)->val_ul;
+
+    if (new_sstep_flags  & ~gdbserver_state.supported_sstep_flags) {
+        put_packet("E22");
+        return;
+    }
+
+    gdbserver_state.sstep_flags = new_sstep_flags;
     put_packet("OK");
 }
 
 static void handle_query_qemu_sstep(GArray *params, void *user_ctx)
 {
-    g_string_printf(gdbserver_state.str_buf, "0x%x", sstep_flags);
+    g_string_printf(gdbserver_state.str_buf, "0x%x",
+                    gdbserver_state.sstep_flags);
     put_strbuf();
 }