replay: introduce breakpoint at the specified step

This patch introduces replay_break, replay_delete_break
qmp and hmp commands.
These commands allow stopping at the specified instruction.
It may be useful for debugging when there are some known
events that should be investigated.
replay_break command has one argument - number of instructions
executed since the start of the replay.
replay_delete_break removes previously set breakpoint.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Acked-by: Markus Armbruster <armbru@redhat.com>

--

v4 changes:
 - removed useless error_free call
Message-Id: <160174520606.12451.7056879546045599378.stgit@pasha-ThinkPad-X280>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hmp-commands.hx

@@ -1804,6 +1804,38 @@ SRST
   Set QOM property *property* of object at location *path* to value *value*
 ERST
 
+    {
+        .name       = "replay_break",
+        .args_type  = "icount:i",
+        .params     = "icount",
+        .help       = "set breakpoint at the specified instruction count",
+        .cmd        = hmp_replay_break,
+    },
+
+SRST
+``replay_break`` *icount*
+  Set replay breakpoint at instruction count *icount*.
+  Execution stops when the specified instruction is reached.
+  There can be at most one breakpoint. When breakpoint is set, any prior
+  one is removed.  The breakpoint may be set only in replay mode and only
+  "in the future", i.e. at instruction counts greater than the current one.
+  The current instruction count can be observed with ``info replay``.
+ERST
+
+    {
+        .name       = "replay_delete_break",
+        .args_type  = "",
+        .params     = "",
+        .help       = "remove replay breakpoint",
+        .cmd        = hmp_replay_delete_break,
+    },
+
+SRST
+``replay_delete_break``
+  Remove replay breakpoint which was previously set with ``replay_break``.
+  The command is ignored when there are no replay breakpoints.
+ERST
+
     {
         .name       = "info",
         .args_type  = "item:s?",

include/monitor/hmp.h

@@ -130,5 +130,7 @@ void hmp_info_vm_generation_id(Monitor *mon, const QDict *qdict);
 void hmp_info_memory_size_summary(Monitor *mon, const QDict *qdict);
 void hmp_info_sev(Monitor *mon, const QDict *qdict);
 void hmp_info_replay(Monitor *mon, const QDict *qdict);
+void hmp_replay_break(Monitor *mon, const QDict *qdict);
+void hmp_replay_delete_break(Monitor *mon, const QDict *qdict);
 
 #endif

qapi/replay.json

@@ -63,3 +63,39 @@
 ##
 { 'command': 'query-replay',
   'returns': 'ReplayInfo' }
+
+##
+# @replay-break:
+#
+# Set replay breakpoint at instruction count @icount.
+# Execution stops when the specified instruction is reached.
+# There can be at most one breakpoint. When breakpoint is set, any prior
+# one is removed.  The breakpoint may be set only in replay mode and only
+# "in the future", i.e. at instruction counts greater than the current one.
+# The current instruction count can be observed with @query-replay.
+#
+# @icount: instruction count to stop at
+#
+# Since: 5.2
+#
+# Example:
+#
+# -> { "execute": "replay-break", "data": { "icount": 220414 } }
+#
+##
+{ 'command': 'replay-break', 'data': { 'icount': 'int' } }
+
+##
+# @replay-delete-break:
+#
+# Remove replay breakpoint which was set with @replay-break.
+# The command is ignored when there are no replay breakpoints.
+#
+# Since: 5.2
+#
+# Example:
+#
+# -> { "execute": "replay-delete-break" }
+#
+##
+{ 'command': 'replay-delete-break' }

replay/replay-debugging.c

@@ -12,10 +12,13 @@
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "sysemu/replay.h"
+#include "sysemu/runstate.h"
 #include "replay-internal.h"
 #include "monitor/hmp.h"
 #include "monitor/monitor.h"
 #include "qapi/qapi-commands-replay.h"
+#include "qapi/qmp/qdict.h"
+#include "qemu/timer.h"
 
 void hmp_info_replay(Monitor *mon, const QDict *qdict)
 {
@@ -41,3 +44,84 @@ ReplayInfo *qmp_query_replay(Error **errp)
     retval->icount = replay_get_current_icount();
     return retval;
 }
+
+static void replay_break(uint64_t icount, QEMUTimerCB callback, void *opaque)
+{
+    assert(replay_mode == REPLAY_MODE_PLAY);
+    assert(replay_mutex_locked());
+    assert(replay_break_icount >= replay_get_current_icount());
+    assert(callback);
+
+    replay_break_icount = icount;
+
+    if (replay_break_timer) {
+        timer_del(replay_break_timer);
+    }
+    replay_break_timer = timer_new_ns(QEMU_CLOCK_REALTIME,
+                                      callback, opaque);
+}
+
+static void replay_delete_break(void)
+{
+    assert(replay_mode == REPLAY_MODE_PLAY);
+    assert(replay_mutex_locked());
+
+    if (replay_break_timer) {
+        timer_del(replay_break_timer);
+        timer_free(replay_break_timer);
+        replay_break_timer = NULL;
+    }
+    replay_break_icount = -1ULL;
+}
+
+static void replay_stop_vm(void *opaque)
+{
+    vm_stop(RUN_STATE_PAUSED);
+    replay_delete_break();
+}
+
+void qmp_replay_break(int64_t icount, Error **errp)
+{
+    if (replay_mode == REPLAY_MODE_PLAY) {
+        if (icount >= replay_get_current_icount()) {
+            replay_break(icount, replay_stop_vm, NULL);
+        } else {
+            error_setg(errp,
+                "cannot set breakpoint at the instruction in the past");
+        }
+    } else {
+        error_setg(errp, "setting the breakpoint is allowed only in play mode");
+    }
+}
+
+void hmp_replay_break(Monitor *mon, const QDict *qdict)
+{
+    int64_t icount = qdict_get_try_int(qdict, "icount", -1LL);
+    Error *err = NULL;
+
+    qmp_replay_break(icount, &err);
+    if (err) {
+        error_report_err(err);
+        return;
+    }
+}
+
+void qmp_replay_delete_break(Error **errp)
+{
+    if (replay_mode == REPLAY_MODE_PLAY) {
+        replay_delete_break();
+    } else {
+        error_setg(errp, "replay breakpoints are allowed only in play mode");
+    }
+}
+
+void hmp_replay_delete_break(Monitor *mon, const QDict *qdict)
+{
+    Error *err = NULL;
+
+    qmp_replay_delete_break(&err);
+    if (err) {
+        error_report_err(err);
+        return;
+    }
+}

replay/replay-internal.h

@@ -94,6 +94,10 @@ extern ReplayState replay_state;
 
 /* File for replay writing */
 extern FILE *replay_file;
+/* Instruction count of the replay breakpoint */
+extern uint64_t replay_break_icount;
+/* Timer for the replay breakpoint callback */
+extern QEMUTimer *replay_break_timer;
 
 void replay_put_byte(uint8_t byte);
 void replay_put_event(uint8_t event);

replay/replay.c

@@ -34,6 +34,10 @@ static char *replay_filename;
 ReplayState replay_state;
 static GSList *replay_blockers;
 
+/* Replay breakpoints */
+uint64_t replay_break_icount = -1ULL;
+QEMUTimer *replay_break_timer;
+
 bool replay_next_event_is(int event)
 {
     bool res = false;
@@ -73,6 +77,13 @@ int replay_get_instructions(void)
     replay_mutex_lock();
     if (replay_next_event_is(EVENT_INSTRUCTION)) {
         res = replay_state.instruction_count;
+        if (replay_break_icount != -1LL) {
+            uint64_t current = replay_get_current_icount();
+            assert(replay_break_icount >= current);
+            if (current + res > replay_break_icount) {
+                res = replay_break_icount - current;
+            }
+        }
     }
     replay_mutex_unlock();
     return res;
@@ -99,6 +110,12 @@ void replay_account_executed_instructions(void)
                    will be read from the log. */
                 qemu_notify_event();
             }
+            /* Execution reached the break step */
+            if (replay_break_icount == replay_state.current_icount) {
+                /* Cannot make callback directly from the vCPU thread */
+                timer_mod_ns(replay_break_timer,
+                    qemu_clock_get_ns(QEMU_CLOCK_REALTIME));
+            }
         }
     }
 }