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[PATCH v4 11/15] gdbstub: add reverse continue support in replay mode
From: |
Pavel Dovgalyuk |
Subject: |
[PATCH v4 11/15] gdbstub: add reverse continue support in replay mode |
Date: |
Mon, 14 Sep 2020 09:07:29 +0300 |
User-agent: |
StGit/0.17.1-dirty |
From: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
This patch adds support of the reverse continue operation for gdbstub.
Reverse continue finds the last breakpoint that would happen in normal
execution from the beginning to the current moment.
Implementation of the reverse continue replays the execution twice:
to find the breakpoints that were hit and to seek to the last breakpoint.
Reverse continue loads the previous snapshot and tries to find the breakpoint
since that moment. If there are no such breakpoints, it proceeds to
the earlier snapshot, and so on. When no breakpoints or watchpoints were
hit at all, execution stops at the beginning of the replay log.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
---
exec.c | 1 +
gdbstub.c | 10 ++++++
include/sysemu/replay.h | 8 +++++
replay/replay-debugging.c | 71 +++++++++++++++++++++++++++++++++++++++++++++
softmmu/cpus.c | 5 +++
stubs/replay.c | 5 +++
6 files changed, 99 insertions(+), 1 deletion(-)
diff --git a/exec.c b/exec.c
index 65983738f2..4333dde185 100644
--- a/exec.c
+++ b/exec.c
@@ -2756,6 +2756,7 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr,
vaddr len,
* Don't process the watchpoints when we are
* in a reverse debugging operation.
*/
+ replay_breakpoint();
return;
}
if (flags == BP_MEM_READ) {
diff --git a/gdbstub.c b/gdbstub.c
index 79e8ccc050..ac92273018 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1907,6 +1907,13 @@ static void handle_backward(GdbCmdContext *gdb_ctx, void
*user_ctx)
put_packet("E14");
}
return;
+ case 'c':
+ if (replay_reverse_continue()) {
+ gdb_continue();
+ } else {
+ put_packet("E14");
+ }
+ return;
}
}
@@ -2161,7 +2168,8 @@ static void handle_query_supported(GdbCmdContext
*gdb_ctx, void *user_ctx)
}
if (replay_mode == REPLAY_MODE_PLAY) {
- g_string_append(gdbserver_state.str_buf, ";ReverseStep+");
+ g_string_append(gdbserver_state.str_buf,
+ ";ReverseStep+;ReverseContinue+");
}
if (gdb_ctx->num_params &&
diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
index 13a8123b09..b6cac175c4 100644
--- a/include/sysemu/replay.h
+++ b/include/sysemu/replay.h
@@ -81,11 +81,19 @@ const char *replay_get_filename(void);
* Returns true on success.
*/
bool replay_reverse_step(void);
+/*
+ * Start searching the last breakpoint/watchpoint.
+ * Used by gdbstub for backwards debugging.
+ * Returns true if the process successfully started.
+ */
+bool replay_reverse_continue(void);
/*
* Returns true if replay module is processing
* reverse_continue or reverse_step request
*/
bool replay_running_debug(void);
+/* Called in reverse debugging mode to collect breakpoint information */
+void replay_breakpoint(void);
/* Processing the instructions */
diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
index f7594a88cd..d02d4e0766 100644
--- a/replay/replay-debugging.c
+++ b/replay/replay-debugging.c
@@ -23,6 +23,8 @@
#include "migration/snapshot.h"
static bool replay_is_debugging;
+static int64_t replay_last_breakpoint;
+static int64_t replay_last_snapshot;
bool replay_running_debug(void)
{
@@ -245,3 +247,72 @@ bool replay_reverse_step(void)
return false;
}
+
+static void replay_continue_end(void)
+{
+ replay_is_debugging = false;
+ vm_stop(RUN_STATE_DEBUG);
+ replay_delete_break();
+}
+
+static void replay_continue_stop(void *opaque)
+{
+ Error *err = NULL;
+ if (replay_last_breakpoint != -1LL) {
+ replay_seek(replay_last_breakpoint, replay_stop_vm_debug, &err);
+ if (err) {
+ error_free(err);
+ replay_continue_end();
+ }
+ return;
+ }
+ /*
+ * No breakpoints since the last snapshot.
+ * Find previous snapshot and try again.
+ */
+ if (replay_last_snapshot != 0) {
+ replay_seek(replay_last_snapshot - 1, replay_continue_stop, &err);
+ if (err) {
+ error_free(err);
+ replay_continue_end();
+ }
+ replay_last_snapshot = replay_get_current_icount();
+ return;
+ } else {
+ /* Seek to the very first step */
+ replay_seek(0, replay_stop_vm_debug, &err);
+ if (err) {
+ error_free(err);
+ replay_continue_end();
+ }
+ return;
+ }
+ replay_continue_end();
+}
+
+bool replay_reverse_continue(void)
+{
+ Error *err = NULL;
+
+ assert(replay_mode == REPLAY_MODE_PLAY);
+
+ if (replay_get_current_icount() != 0) {
+ replay_seek(replay_get_current_icount() - 1, replay_continue_stop,
&err);
+ if (err) {
+ error_free(err);
+ return false;
+ }
+ replay_last_breakpoint = -1LL;
+ replay_is_debugging = true;
+ replay_last_snapshot = replay_get_current_icount();
+ return true;
+ }
+
+ return false;
+}
+
+void replay_breakpoint(void)
+{
+ assert(replay_mode == REPLAY_MODE_PLAY);
+ replay_last_breakpoint = replay_get_current_icount();
+}
diff --git a/softmmu/cpus.c b/softmmu/cpus.c
index dc72f93bc0..756f268993 100644
--- a/softmmu/cpus.c
+++ b/softmmu/cpus.c
@@ -1006,6 +1006,11 @@ static void cpu_handle_guest_debug(CPUState *cpu)
{
if (replay_running_debug()) {
if (!cpu->singlestep_enabled) {
+ /*
+ * Report about the breakpoint and
+ * make a single step to skip it
+ */
+ replay_breakpoint();
cpu_single_step(cpu, SSTEP_ENABLE);
} else {
cpu_single_step(cpu, 0);
diff --git a/stubs/replay.c b/stubs/replay.c
index d5b52302e9..45ebe77fb9 100644
--- a/stubs/replay.c
+++ b/stubs/replay.c
@@ -98,3 +98,8 @@ bool replay_reverse_step(void)
{
return false;
}
+
+bool replay_reverse_continue(void)
+{
+ return false;
+}
- [PATCH v4 01/15] replay: don't record interrupt poll, (continued)
- [PATCH v4 01/15] replay: don't record interrupt poll, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 02/15] replay: provide an accessor for rr filename, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 03/15] qcow2: introduce icount field for snapshots, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 04/15] migration: introduce icount field for snapshots, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 05/15] qapi: introduce replay.json for record/replay-related stuff, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 06/15] replay: introduce info hmp/qmp command, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 07/15] replay: introduce breakpoint at the specified step, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 08/15] replay: implement replay-seek command, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 09/15] replay: flush rr queue before loading the vmstate, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 10/15] gdbstub: add reverse step support in replay mode, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 11/15] gdbstub: add reverse continue support in replay mode,
Pavel Dovgalyuk <=
- [PATCH v4 12/15] replay: describe reverse debugging in docs/replay.txt, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 13/15] docs: convert replay.txt to rst, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 14/15] replay: create temporary snapshot at debugger connection, Pavel Dovgalyuk, 2020/09/14
- [PATCH v4 15/15] tests/acceptance: add reverse debugging test, Pavel Dovgalyuk, 2020/09/14
- Re: [PATCH v4 00/15] Reverse debugging, Paolo Bonzini, 2020/09/20