Pavel Dovgalyuk <pavel.dovgal...@ispras.ru> writes:
> From: Pavel Dovgalyuk <pavel.dovga...@ispras.ru>
>
> 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.
Apropos of the 10/15 thread I currently get:
(gdb) reverse-stepi
warning: Remote failure reply: E14
Program stopped.
_isr_wrapper () at
/home/galak/git/zephyr/arch/arm/core/aarch64/isr_wrapper.S:36
36 in /home/galak/git/zephyr/arch/arm/core/aarch64/isr_wrapper.S
After having manually triggered a loadvm rrstart in the monitor. The
step never happened:
(qemu) loadvm rrstart
loadvm rrstart
(qemu) info replay
info replay
Replaying execution 'record.out': instruction count = 190506
* reverse-stepi called in gdb window *
(qemu) info replay
info replay
Replaying execution 'record.out': instruction count = 190506
(qemu) info snapshots
info snapshots
List of snapshots present on all disks:
ID TAG VM SIZE DATE VM CLOCK
ICOUNT
-- rrstart 653 KiB 2020-09-07 17:12:42 00:00:00.000 0
>
> Signed-off-by: Pavel Dovgalyuk <pavel.dovgal...@ispras.ru>
> ---
> accel/tcg/translator.c | 1 +
> exec.c | 7 ++++++
> gdbstub.c | 55
> +++++++++++++++++++++++++++++++++++++++++++--
> include/sysemu/replay.h | 11 +++++++++
> replay/replay-debugging.c | 33 +++++++++++++++++++++++++++
> softmmu/cpus.c | 14 +++++++++--
> stubs/replay.c | 5 ++++
> 7 files changed, 121 insertions(+), 5 deletions(-)
>
> diff --git a/accel/tcg/translator.c b/accel/tcg/translator.c
> index 603d17ff83..fb1e19c585 100644
> --- a/accel/tcg/translator.c
> +++ b/accel/tcg/translator.c
> @@ -17,6 +17,7 @@
> #include "exec/log.h"
> #include "exec/translator.h"
> #include "exec/plugin-gen.h"
> +#include "sysemu/replay.h"
>
> /* Pairs with tcg_clear_temp_count.
> To be called by #TranslatorOps.{translate_insn,tb_stop} if
> diff --git a/exec.c b/exec.c
> index 7683afb6a8..47512e950c 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2750,6 +2750,13 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr,
> vaddr len,
> QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
> if (watchpoint_address_matches(wp, addr, 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 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 = {
> diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
> index 239c01e7df..13a8123b09 100644
> --- a/include/sysemu/replay.h
> +++ b/include/sysemu/replay.h
> @@ -75,6 +75,17 @@ 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 cfd0221692..aa3ca040e2 100644
> --- a/replay/replay-debugging.c
> +++ b/replay/replay-debugging.c
> @@ -22,6 +22,13 @@
> #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_delete_break();
> +}
> +
> +bool replay_reverse_step(void)
> +{
> + Error *err = NULL;
> +
> + assert(replay_mode == REPLAY_MODE_PLAY);
> +
> + if (replay_get_current_icount() != 0) {
> + replay_seek(replay_get_current_icount() - 1, replay_stop_vm_debug,
> &err);
> + if (err) {
> + error_free(err);
> + return false;
> + }
> + replay_is_debugging = true;
> + return true;
> + }
> +
> + return false;
> +}
> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> index a802e899ab..377fe3298c 100644
> --- a/softmmu/cpus.c
> +++ b/softmmu/cpus.c
> @@ -1004,9 +1004,17 @@ 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/stubs/replay.c b/stubs/replay.c
> index eacb366aa8..d5b52302e9 100644
> --- a/stubs/replay.c
> +++ b/stubs/replay.c
> @@ -93,3 +93,8 @@ uint64_t replay_get_current_icount(void)
> {
> return 0;
> }
> +
> +bool replay_reverse_step(void)
> +{
> + return false;
> +}
--
Alex Bennée
