From f64f2211fb34add52e8d47c1835ac3329731e381 Mon Sep 17 00:00:00 2001
From: yossizap <yossizap@gmail.com>
Date: Tue, 14 Jan 2020 22:46:07 +0000
Subject: [PATCH] Added reverse step and continue support to gdbr ##debug

This feature only works with server implementations that have ReverseStep
and ReverseContinue enabled, such as rr. The official gdbserver doesn't support it.
---
 libr/io/p/io_gdb.c    | 59 +++++++++++++++++++++++++++++++++++++++++++
 shlr/gdb/src/common.c |  4 +++
 2 files changed, 63 insertions(+)

diff --git a/libr/io/p/io_gdb.c b/libr/io/p/io_gdb.c
index e8d36a7ac4..6fda08faaa 100644
--- a/libr/io/p/io_gdb.c
+++ b/libr/io/p/io_gdb.c
@@ -216,6 +216,9 @@ static char *__system(RIO *io, RIODesc *fd, const char *cmd) {
 		eprintf ("Usage: =!cmd args\n"
 			 " =!pid             - show targeted pid\n"
 			 " =!pkt s           - send packet 's'\n"
+			 " =!rd              - show reverse debugging availability\n"
+			 " =!dsb             - step backwards\n"
+			 " =!dcb             - continue backwards\n"
 			 " =!monitor cmd     - hex-encode monitor command and pass"
 			                     " to target interpreter\n"
 			 " =!detach [pid]    - detach from remote/detach specific pid\n"
@@ -270,6 +273,62 @@ static char *__system(RIO *io, RIODesc *fd, const char *cmd) {
 		gdbr_lock_leave (desc);
 		return NULL;
 	}
+	if (r_str_startswith (cmd, "rd")) {
+		PJ *pj = pj_new ();
+		pj_o (pj);
+		pj_kb (pj, "reverse-continue", desc->stub_features.ReverseStep);
+		pj_kb (pj, "reverse-step", desc->stub_features.ReverseContinue);
+		pj_end (pj);
+		io->cb_printf ("%s\n", pj_string (pj));
+		pj_free (pj);
+		return NULL;
+	}
+	if (r_str_startswith (cmd, "dsb")) {
+		if (!desc->stub_features.ReverseStep) {
+			eprintf ("Stepping backwards is not supported in this gdbserver implementation\n");
+			return NULL;
+		}
+		gdbr_lock_enter (desc);
+		if (send_msg (desc, "bs") >= 0) {
+			(void)read_packet (desc);
+			desc->data[desc->data_len] = '\0';
+			if (!desc->no_ack) {
+				eprintf ("[waiting for ack]\n");
+			} else {
+				handle_stop_reason (desc);
+				if (desc->stop_reason.is_valid == false) {
+					eprintf("Thread (%d) stopped for an invalid reason: %d\n",
+						desc->stop_reason.thread, desc->stop_reason.reason);
+				}
+			}
+			gdbr_invalidate_reg_cache ();
+		}
+		gdbr_lock_leave (desc);
+		return NULL;
+	}
+	if (r_str_startswith (cmd, "dcb")) {
+		if (!desc->stub_features.ReverseContinue) {
+			eprintf ("Continue backwards is not supported in this gdbserver implementation\n");
+			return NULL;
+		}
+		gdbr_lock_enter (desc);
+		if (send_msg (desc, "bc") >= 0) {
+			(void)read_packet (desc);
+			desc->data[desc->data_len] = '\0';
+			if (!desc->no_ack) {
+				eprintf ("[waiting for ack]\n");
+			} else {
+				handle_stop_reason (desc);
+				if (desc->stop_reason.is_valid == false) {
+					eprintf("Thread (%d) stopped for an invalid reason: %d\n",
+						desc->stop_reason.thread, desc->stop_reason.reason);
+				}
+			}
+			gdbr_invalidate_reg_cache ();
+		}
+		gdbr_lock_leave (desc);
+		return NULL;
+	}
 	if (r_str_startswith (cmd, "pid")) {
 		int pid = desc ? desc->pid : -1;
 		if (!cmd[3]) {
diff --git a/shlr/gdb/src/common.c b/shlr/gdb/src/common.c
index 20e0b3cf97..65bc121020 100644
--- a/shlr/gdb/src/common.c
+++ b/shlr/gdb/src/common.c
@@ -113,6 +113,10 @@ int handle_qSupported(libgdbr_t *g) {
 		} else if (r_str_startswith (tok, "qEcho")) {
 			g->remote_type = GDB_REMOTE_TYPE_LLDB;
 			g->stub_features.lldb.qEcho = (tok[strlen ("qEcho")] == '+');
+		} else if (r_str_startswith (tok, "ReverseStep")) {
+			g->stub_features.ReverseStep = (tok[strlen ("ReverseStep")] == '+');
+		} else if (r_str_startswith (tok, "ReverseContinue")) {
+			g->stub_features.ReverseContinue = (tok[strlen ("ReverseContinue")] == '+');
 		}
 		// TODO
 		tok = strtok (NULL, ";");