[Qemu-devel] [RFC PATCH v4 10/13] gdbstub: allow reverse execution in gdb stub.

[fred.konrad@greensocs.com]

From: KONRAD Frederic <fred.konrad@greensocs.com>

This allows gdb to reverse step QEMU: reverse-stepi and reverse-cont commands
are allowed.

When step_backward is called, QEMU restores a snapshot before the actual
instruction and stops (with a debug exit) when the previous instruction is
reached.

Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
---
 gdbstub.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/gdbstub.c b/gdbstub.c
index 8afe0b7..99769af 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -33,6 +33,7 @@
 #include "sysemu/char.h"
 #include "sysemu/sysemu.h"
 #include "exec/gdbstub.h"
+#include "reverse-execution.h"
 #endif
 
 #define MAX_PACKET_LENGTH 4096
@@ -1113,6 +1114,17 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
             if (cc->gdb_core_xml_file != NULL) {
                 pstrcat(buf, sizeof(buf), ";qXfer:features:read+");
             }
+
+            #ifndef CONFIG_USER_ONLY
+            /*
+             * When reverse execution is enabled those additional features must
+             * be set so GDB allows reverse-stepi and reverse-continue command.
+             */
+            if (cexe_is_enabled()) {
+                pstrcat(buf, sizeof(buf), ";ReverseStep+;ReverseContinue+");
+            }
+            #endif /* !CONFIG_USER_ONLY */
+
             put_packet(s, buf);
             break;
         }
@@ -1161,7 +1173,23 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
         }
         /* Unrecognised 'q' command.  */
         goto unknown_command;
-
+    #ifndef CONFIG_USER_ONLY
+    case 'b':
+        /* Reverse execution. */
+        switch (*p) {
+        case 's':
+            cexe_step_backward(s->c_cpu, 1);
+            break;
+        case 'c':
+            cexe_continue_backward(s->c_cpu);
+            break;
+        default:
+            buf[0] = '\0';
+            put_packet(s, buf);
+            break;
+        }
+        break;
+    #endif /* !CONFIG_USER_ONLY */
     default:
     unknown_command:
         /* put empty packet */
@@ -1221,6 +1249,7 @@ static void gdb_vm_state_change(void *opaque, int running, RunState state)
         ret = GDB_SIGNAL_TRAP;
         break;
     case RUN_STATE_PAUSED:
+        cexe_stop_reverse_continue();
         ret = GDB_SIGNAL_INT;
         break;
     case RUN_STATE_SHUTDOWN:
-- 
1.9.0