diff mbox series

[v12,16/25] gdbstub: add reverse step support in replay mode

Message ID 154935487327.7509.5368327029472083307.stgit@pasha-VirtualBox
State New
Headers show
Series Fixing record/replay and adding reverse debugging | expand

Commit Message

Pavel Dovgalyuk Feb. 5, 2019, 8:21 a.m. UTC
GDB remote protocol supports two reverse debugging commands:
reverse step and reverse continue.
This patch adds support of the first one to the gdbstub.
Reverse step is intended to step one instruction in the backwards
direction. This is not possible in regular execution.
But replayed execution is deterministic, therefore we can load one of
the prior snapshots and proceed to the desired step. It is equivalent
to stepping one instruction back.
There should be at least one snapshot preceding the debugged part of
the replay log.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
---
 accel/tcg/translator.c    |    1 +
 cpus.c                    |   14 +++++++++++---
 exec.c                    |    7 +++++++
 gdbstub.c                 |   44 +++++++++++++++++++++++++++++++++++++++++---
 include/sysemu/replay.h   |   11 +++++++++++
 replay/replay-debugging.c |   33 +++++++++++++++++++++++++++++++++
 stubs/replay.c            |    5 +++++
 7 files changed, 109 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/accel/tcg/translator.c b/accel/tcg/translator.c
index afd0a49ea6..33a543e82f 100644
--- a/accel/tcg/translator.c
+++ b/accel/tcg/translator.c
@@ -17,6 +17,7 @@ 
 #include "exec/gen-icount.h"
 #include "exec/log.h"
 #include "exec/translator.h"
+#include "sysemu/replay.h"
 
 /* Pairs with tcg_clear_temp_count.
    To be called by #TranslatorOps.{translate_insn,tb_stop} if
diff --git a/cpus.c b/cpus.c
index aa33fb15b3..013341ca4f 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1104,9 +1104,17 @@  static bool cpu_can_run(CPUState *cpu)
 
 static void cpu_handle_guest_debug(CPUState *cpu)
 {
-    gdb_set_stop_cpu(cpu);
-    qemu_system_debug_request();
-    cpu->stopped = true;
+    if (!replay_running_debug()) {
+        gdb_set_stop_cpu(cpu);
+        qemu_system_debug_request();
+        cpu->stopped = true;
+    } else {
+        if (!cpu->singlestep_enabled) {
+            cpu_single_step(cpu, SSTEP_ENABLE);
+        } else {
+            cpu_single_step(cpu, 0);
+        }
+    }
 }
 
 #ifdef CONFIG_LINUX
diff --git a/exec.c b/exec.c
index 03dd673d36..fdbd65c5b8 100644
--- a/exec.c
+++ b/exec.c
@@ -2742,6 +2742,13 @@  static void check_watchpoint(int offset, int len, MemTxAttrs attrs, int flags)
     QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
         if (cpu_watchpoint_address_matches(wp, vaddr, len)
             && (wp->flags & flags)) {
+            if (replay_running_debug()) {
+                /*
+                 * Don't process the watchpoints when we are
+                 * in a reverse debugging operation.
+                 */
+                return;
+            }
             if (flags == BP_MEM_READ) {
                 wp->flags |= BP_WATCHPOINT_HIT_READ;
             } else {
diff --git a/gdbstub.c b/gdbstub.c
index 3129b5c284..d9bf3863c1 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -39,6 +39,7 @@ 
 #include "sysemu/kvm.h"
 #include "exec/semihost.h"
 #include "exec/exec-all.h"
+#include "sysemu/replay.h"
 
 #ifdef CONFIG_USER_ONLY
 #define GDB_ATTACHED "0"
@@ -344,6 +345,20 @@  typedef struct GDBState {
  */
 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;
 
 bool gdb_has_xml;
@@ -434,7 +449,7 @@  static int gdb_continue_partial(GDBState *s, 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, get_sstep_flags());
         }
     }
     s->running_state = 1;
@@ -453,7 +468,7 @@  static int gdb_continue_partial(GDBState *s, char *newstates)
                 break; /* nothing to do here */
             case 's':
                 trace_gdbstub_op_stepping(cpu->cpu_index);
-                cpu_single_step(cpu, sstep_flags);
+                cpu_single_step(cpu, get_sstep_flags());
                 cpu_resume(cpu);
                 flag = 1;
                 break;
@@ -1409,9 +1424,28 @@  static int gdb_handle_packet(GDBState *s, const char *line_buf)
             addr = strtoull(p, (char **)&p, 16);
             gdb_set_cpu_pc(s, addr);
         }
-        cpu_single_step(s->c_cpu, sstep_flags);
+        cpu_single_step(s->c_cpu, get_sstep_flags());
         gdb_continue(s);
         return RS_IDLE;
+    case 'b':
+        /* Backward debugging commands */
+        if (replay_mode == REPLAY_MODE_PLAY) {
+            switch (*p) {
+            case 's':
+                if (replay_reverse_step()) {
+                    gdb_continue(s);
+                    return RS_IDLE;
+                } else {
+                    put_packet(s, "E14");
+                    break;
+                }
+            default:
+                goto unknown_command;
+            }
+        } else {
+            put_packet(s, "E22");
+        }
+        goto unknown_command;
     case 'F':
         {
             target_ulong ret;
@@ -1714,6 +1748,10 @@  static int gdb_handle_packet(GDBState *s, const char *line_buf)
             }
             pstrcat(buf, sizeof(buf), ";multiprocess+");
 
+            if (replay_mode == REPLAY_MODE_PLAY) {
+                pstrcat(buf, sizeof(buf), ";ReverseStep+");
+            }
+
             put_packet(s, buf);
             break;
         }
diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
index d7e859d915..533003f2b0 100644
--- a/include/sysemu/replay.h
+++ b/include/sysemu/replay.h
@@ -73,6 +73,17 @@  void replay_finish(void);
 void replay_add_blocker(Error *reason);
 /* Returns name of the replay log file */
 const char *replay_get_filename(void);
+/*
+ * Start making one step in backward direction.
+ * Used by gdbstub for backwards debugging.
+ * Returns true on success.
+ */
+bool replay_reverse_step(void);
+/*
+ * Returns true if replay module is processing
+ * reverse_continue or reverse_step request
+ */
+bool replay_running_debug(void);
 
 /* Processing the instructions */
 
diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
index e3821ab1ba..0c7e34f50f 100644
--- a/replay/replay-debugging.c
+++ b/replay/replay-debugging.c
@@ -21,6 +21,13 @@ 
 #include "block/snapshot.h"
 #include "migration/snapshot.h"
 
+static bool replay_is_debugging;
+
+bool replay_running_debug(void)
+{
+    return replay_is_debugging;
+}
+
 void hmp_info_replay(Monitor *mon, const QDict *qdict)
 {
     if (replay_mode == REPLAY_MODE_NONE) {
@@ -219,3 +226,29 @@  void hmp_replay_seek(Monitor *mon, const QDict *qdict)
         return;
     }
 }
+
+static void replay_stop_vm_debug(void *opaque)
+{
+    replay_is_debugging = false;
+    vm_stop(RUN_STATE_DEBUG);
+    replay_break(-1LL, NULL, NULL);
+}
+
+bool replay_reverse_step(void)
+{
+    Error *err = NULL;
+
+    assert(replay_mode == REPLAY_MODE_PLAY);
+
+    if (replay_get_current_step() != 0) {
+        replay_seek(replay_get_current_step() - 1, replay_stop_vm_debug, &err);
+        if (err) {
+            error_free(err);
+            return false;
+        }
+        replay_is_debugging = true;
+        return true;
+    }
+
+    return false;
+}
diff --git a/stubs/replay.c b/stubs/replay.c
index 4ac607895d..521552fa83 100644
--- a/stubs/replay.c
+++ b/stubs/replay.c
@@ -80,3 +80,8 @@  void replay_mutex_lock(void)
 void replay_mutex_unlock(void)
 {
 }
+
+bool replay_reverse_step(void)
+{
+    return false;
+}