gdbstub: abstract target specific details from gdb_put_packet_binary

We unfortunately handle the checking of packet acknowledgement
differently for user and softmmu modes. Abstract the user mode stuff
behind gdb_got_immediate_ack with a stub for softmmu.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230302190846.2593720-14-alex.bennee@linaro.org>
Message-Id: <20230303025805.625589-14-richard.henderson@linaro.org>

gdbstub/gdbstub.c

@@ -239,15 +239,9 @@ int gdb_put_packet_binary(const char *buf, int len, bool dump)
         gdb_put_buffer(gdbserver_state.last_packet->data,
                    gdbserver_state.last_packet->len);
 
-#ifdef CONFIG_USER_ONLY
-        i = gdb_get_char();
-        if (i < 0)
-            return -1;
-        if (i == '+')
+        if (gdb_got_immediate_ack()) {
             break;
-#else
-        break;
-#endif
+        }
     }
     return 0;
 }

gdbstub/internals.h

@@ -110,6 +110,21 @@ void gdb_memtohex(GString *buf, const uint8_t *mem, int len);
 void gdb_memtox(GString *buf, const char *mem, int len);
 void gdb_read_byte(uint8_t ch);
 
+/*
+ * Packet acknowledgement - we handle this slightly differently
+ * between user and softmmu mode, mainly to deal with the differences
+ * between the flexible chardev and the direct fd approaches.
+ *
+ * We currently don't support a negotiated QStartNoAckMode
+ */
+
+/**
+ * gdb_got_immediate_ack() - check ok to continue
+ *
+ * Returns true to continue, false to re-transmit for user only, the
+ * softmmu stub always returns true.
+ */
+bool gdb_got_immediate_ack(void);
 /* utility helpers */
 CPUState *gdb_first_attached_cpu(void);
 void gdb_append_thread_id(CPUState *cpu, GString *buf);

gdbstub/softmmu.c

@@ -55,6 +55,14 @@ int gdb_get_cpu_index(CPUState *cpu)
     return cpu->cpu_index + 1;
 }
 
+/*
+ * We check the status of the last message in the chardev receive code
+ */
+bool gdb_got_immediate_ack(void)
+{
+    return true;
+}
+
 /*
  * GDB Connection management. For system emulation we do all of this
  * via our existing Chardev infrastructure which allows us to support

gdbstub/user.c

@@ -54,6 +54,25 @@ int gdb_get_char(void)
     return ch;
 }
 
+bool gdb_got_immediate_ack(void)
+{
+    int i;
+
+    i = gdb_get_char();
+    if (i < 0) {
+        /* no response, continue anyway */
+        return true;
+    }
+
+    if (i == '+') {
+        /* received correctly, continue */
+        return true;
+    }
+
+    /* anything else, including '-' then try again */
+    return false;
+}
+
 void gdb_put_buffer(const uint8_t *buf, int len)
 {
     int ret;