From fda8458bd3a9cb3108ba2f09921b6e3eee0d1bf3 Mon Sep 17 00:00:00 2001 From: Pavel Dovgalyuk Date: Sat, 3 Oct 2020 20:13:43 +0300 Subject: gdbstub: add reverse step support in replay mode MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Alex Bennée -- v4 changes: - inverted condition in cpu_handle_guest_debug (suggested by Alex Bennée) Message-Id: <160174522341.12451.1498758422543765253.stgit@pasha-ThinkPad-X280> Signed-off-by: Paolo Bonzini --- gdbstub.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 53 insertions(+), 2 deletions(-) (limited to 'gdbstub.c') diff --git a/gdbstub.c b/gdbstub.c index 9dfb6e4142..79e8ccc050 100644 --- a/gdbstub.c +++ b/gdbstub.c @@ -51,6 +51,7 @@ #include "sysemu/runstate.h" #include "hw/semihosting/semihost.h" #include "exec/exec-all.h" +#include "sysemu/replay.h" #ifdef CONFIG_USER_ONLY #define GDB_ATTACHED "0" @@ -375,6 +376,20 @@ 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; static void init_gdbserver_state(void) @@ -501,7 +516,7 @@ static int gdb_continue_partial(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; @@ -1874,10 +1889,31 @@ static void handle_step(GdbCmdContext *gdb_ctx, void *user_ctx) gdb_set_cpu_pc((target_ulong)gdb_ctx->params[0].val_ull); } - cpu_single_step(gdbserver_state.c_cpu, sstep_flags); + cpu_single_step(gdbserver_state.c_cpu, get_sstep_flags()); gdb_continue(); } +static void handle_backward(GdbCmdContext *gdb_ctx, void *user_ctx) +{ + if (replay_mode != REPLAY_MODE_PLAY) { + put_packet("E22"); + } + if (gdb_ctx->num_params == 1) { + switch (gdb_ctx->params[0].opcode) { + case 's': + if (replay_reverse_step()) { + gdb_continue(); + } else { + put_packet("E14"); + } + return; + } + } + + /* Default invalid command */ + put_packet(""); +} + static void handle_v_cont_query(GdbCmdContext *gdb_ctx, void *user_ctx) { put_packet("vCont;c;C;s;S"); @@ -2124,6 +2160,10 @@ static void handle_query_supported(GdbCmdContext *gdb_ctx, void *user_ctx) g_string_append(gdbserver_state.str_buf, ";qXfer:features:read+"); } + if (replay_mode == REPLAY_MODE_PLAY) { + g_string_append(gdbserver_state.str_buf, ";ReverseStep+"); + } + if (gdb_ctx->num_params && strstr(gdb_ctx->params[0].data, "multiprocess+")) { gdbserver_state.multiprocess = true; @@ -2460,6 +2500,17 @@ static int gdb_handle_packet(const char *line_buf) cmd_parser = &step_cmd_desc; } break; + case 'b': + { + static const GdbCmdParseEntry backward_cmd_desc = { + .handler = handle_backward, + .cmd = "b", + .cmd_startswith = 1, + .schema = "o0" + }; + cmd_parser = &backward_cmd_desc; + } + break; case 'F': { static const GdbCmdParseEntry file_io_cmd_desc = { -- cgit v1.2.3 From cda382594b7ea50aff5f672f32767f9f9fef4c12 Mon Sep 17 00:00:00 2001 From: Pavel Dovgalyuk Date: Sat, 3 Oct 2020 20:13:49 +0300 Subject: gdbstub: add reverse continue support in replay mode 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 Message-Id: <160174522930.12451.6994758004725016836.stgit@pasha-ThinkPad-X280> Signed-off-by: Paolo Bonzini --- gdbstub.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'gdbstub.c') 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 && -- cgit v1.2.3 From 56357d80fc713367ace8251d1350a490e204bc3a Mon Sep 17 00:00:00 2001 From: Pavel Dovgalyuk Date: Sat, 3 Oct 2020 20:14:01 +0300 Subject: replay: create temporary snapshot at debugger connection MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When record/replay does not uses overlays for storing the snapshots, user is not capable of issuing reverse debugging commands. This patch adds creation of the VM snapshot on the temporary overlay image, when the debugger connects to QEMU. Therefore the execution can be rewind to the moment of the debugger connection while debugging the virtual machine. Signed-off-by: Pavel Dovgalyuk -- v6: - dropped unused error processing (suggested by Philippe Mathieu-Daudé) Message-Id: <160174524096.12451.11651270339216758643.stgit@pasha-ThinkPad-X280> Signed-off-by: Paolo Bonzini --- gdbstub.c | 1 + 1 file changed, 1 insertion(+) (limited to 'gdbstub.c') diff --git a/gdbstub.c b/gdbstub.c index ac92273018..f19f98ab1a 100644 --- a/gdbstub.c +++ b/gdbstub.c @@ -3321,6 +3321,7 @@ static void gdb_chr_event(void *opaque, QEMUChrEvent event) s->g_cpu = s->c_cpu; vm_stop(RUN_STATE_PAUSED); + replay_gdb_attached(); gdb_has_xml = false; break; default: -- cgit v1.2.3