gdbstub: move sstep flags probing into AccelClass

The support of single-stepping is very much dependent on support from
the accelerator we are using. To avoid special casing in gdbstub move
the probing out to an AccelClass function so future accelerators can
put their code there.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Mads Ynddal <mads@ynddal.dk>
Message-Id: <20220929114231.583801-44-alex.bennee@linaro.org>

accel/accel-common.c

@@ -129,6 +129,16 @@ bool accel_cpu_realizefn(CPUState *cpu, Error **errp)
     return true;
 }
 
+int accel_supported_gdbstub_sstep_flags(void)
+{
+    AccelState *accel = current_accel();
+    AccelClass *acc = ACCEL_GET_CLASS(accel);
+    if (acc->gdbstub_supported_sstep_flags) {
+        return acc->gdbstub_supported_sstep_flags();
+    }
+    return 0;
+}
+
 static const TypeInfo accel_cpu_type = {
     .name = TYPE_ACCEL_CPU,
     .parent = TYPE_OBJECT,

accel/kvm/kvm-all.c

@@ -175,7 +175,7 @@ bool kvm_direct_msi_allowed;
 bool kvm_ioeventfd_any_length_allowed;
 bool kvm_msi_use_devid;
 bool kvm_has_guest_debug;
-int kvm_sstep_flags;
+static int kvm_sstep_flags;
 static bool kvm_immediate_exit;
 static hwaddr kvm_max_slot_size = ~0;
 
@@ -3712,6 +3712,17 @@ static void kvm_accel_instance_init(Object *obj)
     s->kvm_dirty_ring_size = 0;
 }
 
+/**
+ * kvm_gdbstub_sstep_flags():
+ *
+ * Returns: SSTEP_* flags that KVM supports for guest debug. The
+ * support is probed during kvm_init()
+ */
+static int kvm_gdbstub_sstep_flags(void)
+{
+    return kvm_sstep_flags;
+}
+
 static void kvm_accel_class_init(ObjectClass *oc, void *data)
 {
     AccelClass *ac = ACCEL_CLASS(oc);
@@ -3719,6 +3730,7 @@ static void kvm_accel_class_init(ObjectClass *oc, void *data)
     ac->init_machine = kvm_init;
     ac->has_memory = kvm_accel_has_memory;
     ac->allowed = &kvm_allowed;
+    ac->gdbstub_supported_sstep_flags = kvm_gdbstub_sstep_flags;
 
     object_class_property_add(oc, "kernel-irqchip", "on|off|split",
         NULL, kvm_set_kernel_irqchip,

accel/tcg/tcg-all.c

@@ -25,6 +25,7 @@
 
 #include "qemu/osdep.h"
 #include "sysemu/tcg.h"
+#include "sysemu/replay.h"
 #include "sysemu/cpu-timers.h"
 #include "tcg/tcg.h"
 #include "qapi/error.h"
@@ -207,12 +208,28 @@ static void tcg_set_splitwx(Object *obj, bool value, Error **errp)
     s->splitwx_enabled = value;
 }
 
+static int tcg_gdbstub_supported_sstep_flags(void)
+{
+    /*
+     * 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) {
+        return SSTEP_ENABLE;
+    } else {
+        return SSTEP_ENABLE | SSTEP_NOIRQ | SSTEP_NOTIMER;
+    }
+}
+
 static void tcg_accel_class_init(ObjectClass *oc, void *data)
 {
     AccelClass *ac = ACCEL_CLASS(oc);
     ac->name = "tcg";
     ac->init_machine = tcg_init_machine;
     ac->allowed = &tcg_allowed;
+    ac->gdbstub_supported_sstep_flags = tcg_gdbstub_supported_sstep_flags;
 
     object_class_property_add_str(oc, "thread",
                                   tcg_get_thread,

gdbstub/gdbstub.c

@@ -383,27 +383,13 @@ static void init_gdbserver_state(void)
     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 if (kvm_enabled()) {
-        gdbserver_state.supported_sstep_flags = kvm_get_supported_sstep_flags();
-    } 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.
+     * What single-step modes are supported is accelerator dependent.
+     * By default try to use no IRQs and no timers while single
+     * stepping so as to make single stepping like a typical ICE HW step.
      */
+    gdbserver_state.supported_sstep_flags = accel_supported_gdbstub_sstep_flags();
     gdbserver_state.sstep_flags = SSTEP_ENABLE | SSTEP_NOIRQ | SSTEP_NOTIMER;
     gdbserver_state.sstep_flags &= gdbserver_state.supported_sstep_flags;
-
 }
 
 #ifndef CONFIG_USER_ONLY

include/qemu/accel.h

@@ -43,6 +43,10 @@ typedef struct AccelClass {
     bool (*has_memory)(MachineState *ms, AddressSpace *as,
                        hwaddr start_addr, hwaddr size);
 #endif
+
+    /* gdbstub related hooks */
+    int (*gdbstub_supported_sstep_flags)(void);
+
     bool *allowed;
     /*
      * Array of global properties that would be applied when specific
@@ -92,4 +96,12 @@ void accel_cpu_instance_init(CPUState *cpu);
  */
 bool accel_cpu_realizefn(CPUState *cpu, Error **errp);
 
+/**
+ * accel_supported_gdbstub_sstep_flags:
+ *
+ * Returns the supported single step modes for the configured
+ * accelerator.
+ */
+int accel_supported_gdbstub_sstep_flags(void);
+
 #endif /* QEMU_ACCEL_H */

include/sysemu/kvm.h

@@ -47,7 +47,6 @@ extern bool kvm_direct_msi_allowed;
 extern bool kvm_ioeventfd_any_length_allowed;
 extern bool kvm_msi_use_devid;
 extern bool kvm_has_guest_debug;
-extern int kvm_sstep_flags;
 
 #define kvm_enabled()           (kvm_allowed)
 /**
@@ -174,12 +173,6 @@ extern int kvm_sstep_flags;
  */
 #define kvm_supports_guest_debug() (kvm_has_guest_debug)
 
-/*
- * kvm_supported_sstep_flags
- * Returns: SSTEP_* flags that KVM supports for guest debug
- */
-#define kvm_get_supported_sstep_flags() (kvm_sstep_flags)
-
 #else
 
 #define kvm_enabled()           (0)
@@ -198,7 +191,6 @@ extern int kvm_sstep_flags;
 #define kvm_ioeventfd_any_length_enabled() (false)
 #define kvm_msi_devid_required() (false)
 #define kvm_supports_guest_debug() (false)
-#define kvm_get_supported_sstep_flags() (0)
 
 #endif  /* CONFIG_KVM_IS_POSSIBLE */