[Qemu-devel] [PATCH v6 10/25] replay: introduce breakpoint at the specified step

[Pavel Dovgalyuk]

This patch introduces replay_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.
The commands have one argument - number of instructions
executed since the start of the replay.

Signed-off-by: Pavel Dovgalyuk <address@hidden>

--

v2:
 - renamed replay_break qmp command into replay-break
   (suggested by Eric Blake)
---
 hmp-commands.hx           |   15 ++++++++++++
 hmp.h                     |    1 +
 include/sysemu/replay.h   |    3 ++
 qapi/misc.json            |   17 ++++++++++++++
 replay/replay-debugging.c |   55 +++++++++++++++++++++++++++++++++++++++++++++
 replay/replay-internal.h  |    4 +++
 replay/replay.c           |   17 ++++++++++++++
 7 files changed, 112 insertions(+)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index db0c681..aa0794e 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1888,6 +1888,21 @@ Set QOM property @var{property} of object at location 
@var{path} to value @var{v
 ETEXI
 
     {
+        .name       = "replay_break",
+        .args_type  = "step:i",
+        .params     = "step",
+        .help       = "sets breakpoint on the specified step of the replay",
+        .cmd        = hmp_replay_break,
+    },
+
+STEXI
address@hidden replay_break @var{step}
address@hidden replay_break
+Set breakpoint on the specified step of the replay.
+Execution stops when the specified step is reached.
+ETEXI
+
+    {
         .name       = "info",
         .args_type  = "item:s?",
         .params     = "[subcommand]",
diff --git a/hmp.h b/hmp.h
index d792149..ad94abe 100644
--- a/hmp.h
+++ b/hmp.h
@@ -149,5 +149,6 @@ 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);
 
 #endif
diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
index a5510f2..c9ba75a 100644
--- a/include/sysemu/replay.h
+++ b/include/sysemu/replay.h
@@ -73,6 +73,9 @@ void replay_finish(void);
 void replay_add_blocker(Error *reason);
 /*! Returns name of the replay log file */
 const char *replay_get_filename(void);
+/*! Sets breakpoint at the specified step.
+    If step = -1LL the existing breakpoint is removed. */
+void replay_break(int64_t step, QEMUTimerCB callback, void *opaque);
 
 /* Processing the instructions */
 
diff --git a/qapi/misc.json b/qapi/misc.json
index e246ce3..4fcd211 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -3135,6 +3135,23 @@
   'returns': 'ReplayInfo' }
 
 ##
+# @replay-break:
+#
+# Set breakpoint on the specified step of the replay.
+# Execution stops when the specified step is reached.
+#
+# @step: execution step to stop at
+#
+# Since: 3.1
+#
+# Example:
+#
+# -> { "execute": "replay-break", "data": { "step": 220414 } }
+#
+##
+{ 'command': 'replay-break', 'data': { 'step': 'int' } }
+
+##
 # @xen-load-devices-state:
 #
 # Load the state of all devices from file. The RAM and the block devices
diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
index 2d364fa..c6b80c0 100644
--- a/replay/replay-debugging.c
+++ b/replay/replay-debugging.c
@@ -16,6 +16,8 @@
 #include "hmp.h"
 #include "monitor/monitor.h"
 #include "qapi/qapi-commands-misc.h"
+#include "qapi/qmp/qdict.h"
+#include "qemu/timer.h"
 
 void hmp_info_replay(Monitor *mon, const QDict *qdict)
 {
@@ -39,3 +41,56 @@ ReplayInfo *qmp_query_replay(Error **errp)
     retval->step = replay_get_current_step();
     return retval;
 }
+
+void replay_break(int64_t step, QEMUTimerCB callback, void *opaque)
+{
+    assert(replay_mode == REPLAY_MODE_PLAY);
+    assert(replay_mutex_locked());
+
+    replay_break_step = step;
+    if (replay_break_timer) {
+        timer_del(replay_break_timer);
+        timer_free(replay_break_timer);
+        replay_break_timer = NULL;
+    }
+
+    if (replay_break_step == -1LL) {
+        return;
+    }
+    assert(replay_break_step >= replay_get_current_step());
+    assert(callback);
+
+    replay_break_timer = timer_new_ns(QEMU_CLOCK_REALTIME, callback, opaque);
+}
+
+static void replay_stop_vm(void *opaque)
+{
+    vm_stop(RUN_STATE_PAUSED);
+    replay_break(-1LL, NULL, NULL);
+}
+
+void qmp_replay_break(int64_t step, Error **errp)
+{
+    if (replay_mode ==  REPLAY_MODE_PLAY) {
+        if (step >= replay_get_current_step()) {
+            replay_break(step, replay_stop_vm, NULL);
+        } else {
+            error_setg(errp, "cannot set break at the step in the past");
+        }
+    } else {
+        error_setg(errp, "setting the break is allowed only in play mode");
+    }
+}
+
+void hmp_replay_break(Monitor *mon, const QDict *qdict)
+{
+    int64_t step = qdict_get_try_int(qdict, "step", -1LL);
+    Error *err = NULL;
+
+    qmp_replay_break(step, &err);
+    if (err) {
+        monitor_printf(mon, "replay_break error: %s\n", error_get_pretty(err));
+        error_free(err);
+        return;
+    }
+}
diff --git a/replay/replay-internal.h b/replay/replay-internal.h
index 4f82676..f9cad9d 100644
--- a/replay/replay-internal.h
+++ b/replay/replay-internal.h
@@ -91,6 +91,10 @@ extern ReplayState replay_state;
 
 /* File for replay writing */
 extern FILE *replay_file;
+/*! Step of the replay breakpoint */
+extern int64_t replay_break_step;
+/*! 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);
diff --git a/replay/replay.c b/replay/replay.c
index 80afbd5..a106211 100644
--- a/replay/replay.c
+++ b/replay/replay.c
@@ -34,6 +34,10 @@ static char *replay_filename;
 ReplayState replay_state;
 static GSList *replay_blockers;
 
+/* Replay breakpoints */
+int64_t replay_break_step = -1LL;
+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.instructions_count;
+        if (replay_break_step != -1LL) {
+            uint64_t current = replay_get_current_step();
+            assert(replay_break_step >= current);
+            if (current + res > replay_break_step) {
+                res = replay_break_step - 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_step == replay_state.current_step) {
+                /* Cannot make callback directly from the vCPU thread */
+                timer_mod_ns(replay_break_timer,
+                    qemu_clock_get_ns(QEMU_CLOCK_REALTIME));
+            }
         }
     }
 }