From 758370052fb602f9f23c3b8ae26a6133373c78e6 Mon Sep 17 00:00:00 2001 From: Matheus Tavares Bernardino Date: Thu, 4 May 2023 12:37:31 -0300 Subject: [PATCH] gdbstub: only send stop-reply packets when allowed to MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit GDB's remote serial protocol allows stop-reply messages to be sent by the stub either as a notification packet or as a reply to a GDB command (provided that the cmd accepts such a response). QEMU currently does not implement notification packets, so it should only send stop-replies synchronously and when requested. Nevertheless, it still issues unsolicited stop messages through gdb_vm_state_change(). Although this behavior doesn't seem to cause problems with GDB itself (the messages are just ignored), it can impact other debuggers that implement the GDB remote serial protocol, like hexagon-lldb. Let's change the gdbstub to send stop messages only as a response to a previous GDB command that accepts such a reply. Signed-off-by: Matheus Tavares Bernardino Acked-by: Alex Bennée Signed-off-by: Taylor Simpson Message-Id: --- gdbstub/gdbstub.c | 37 ++++++++++++++++++++++++++++--------- gdbstub/internals.h | 5 +++++ gdbstub/softmmu.c | 13 +++++++++++-- gdbstub/user.c | 24 ++++++++++++++++-------- 4 files changed, 60 insertions(+), 19 deletions(-) diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c index 0760d78685..be18568d0a 100644 --- a/gdbstub/gdbstub.c +++ b/gdbstub/gdbstub.c @@ -777,6 +777,10 @@ typedef void (*GdbCmdHandler)(GArray *params, void *user_ctx); /* * cmd_startswith -> cmd is compared using startswith * + * allow_stop_reply -> true iff the gdbstub can respond to this command with a + * "stop reply" packet. The list of commands that accept such response is + * defined at the GDB Remote Serial Protocol documentation. see: + * https://sourceware.org/gdb/onlinedocs/gdb/Stop-Reply-Packets.html#Stop-Reply-Packets. * * schema definitions: * Each schema parameter entry consists of 2 chars, @@ -802,6 +806,7 @@ typedef struct GdbCmdParseEntry { const char *cmd; bool cmd_startswith; const char *schema; + bool allow_stop_reply; } GdbCmdParseEntry; static inline int startswith(const char *string, const char *pattern) @@ -835,6 +840,7 @@ static int process_string_cmd(void *user_ctx, const char *data, } } + gdbserver_state.allow_stop_reply = cmd->allow_stop_reply; cmd->handler(params, user_ctx); return 0; } @@ -1283,11 +1289,14 @@ static void handle_v_attach(GArray *params, void *user_ctx) gdbserver_state.g_cpu = cpu; gdbserver_state.c_cpu = cpu; - g_string_printf(gdbserver_state.str_buf, "T%02xthread:", GDB_SIGNAL_TRAP); - gdb_append_thread_id(cpu, gdbserver_state.str_buf); - g_string_append_c(gdbserver_state.str_buf, ';'); + if (gdbserver_state.allow_stop_reply) { + g_string_printf(gdbserver_state.str_buf, "T%02xthread:", GDB_SIGNAL_TRAP); + gdb_append_thread_id(cpu, gdbserver_state.str_buf); + g_string_append_c(gdbserver_state.str_buf, ';'); + gdbserver_state.allow_stop_reply = false; cleanup: - gdb_put_strbuf(); + gdb_put_strbuf(); + } } static void handle_v_kill(GArray *params, void *user_ctx) @@ -1310,12 +1319,14 @@ static const GdbCmdParseEntry gdb_v_commands_table[] = { .handler = handle_v_cont, .cmd = "Cont", .cmd_startswith = 1, + .allow_stop_reply = true, .schema = "s0" }, { .handler = handle_v_attach, .cmd = "Attach;", .cmd_startswith = 1, + .allow_stop_reply = true, .schema = "l0" }, { @@ -1698,10 +1709,13 @@ static void handle_gen_set(GArray *params, void *user_ctx) static void handle_target_halt(GArray *params, void *user_ctx) { - g_string_printf(gdbserver_state.str_buf, "T%02xthread:", GDB_SIGNAL_TRAP); - gdb_append_thread_id(gdbserver_state.c_cpu, gdbserver_state.str_buf); - g_string_append_c(gdbserver_state.str_buf, ';'); - gdb_put_strbuf(); + if (gdbserver_state.allow_stop_reply) { + g_string_printf(gdbserver_state.str_buf, "T%02xthread:", GDB_SIGNAL_TRAP); + gdb_append_thread_id(gdbserver_state.c_cpu, gdbserver_state.str_buf); + g_string_append_c(gdbserver_state.str_buf, ';'); + gdb_put_strbuf(); + gdbserver_state.allow_stop_reply = false; + } /* * Remove all the breakpoints when this query is issued, * because gdb is doing an initial connect and the state @@ -1725,7 +1739,8 @@ static int gdb_handle_packet(const char *line_buf) static const GdbCmdParseEntry target_halted_cmd_desc = { .handler = handle_target_halt, .cmd = "?", - .cmd_startswith = 1 + .cmd_startswith = 1, + .allow_stop_reply = true, }; cmd_parser = &target_halted_cmd_desc; } @@ -1736,6 +1751,7 @@ static int gdb_handle_packet(const char *line_buf) .handler = handle_continue, .cmd = "c", .cmd_startswith = 1, + .allow_stop_reply = true, .schema = "L0" }; cmd_parser = &continue_cmd_desc; @@ -1747,6 +1763,7 @@ static int gdb_handle_packet(const char *line_buf) .handler = handle_cont_with_sig, .cmd = "C", .cmd_startswith = 1, + .allow_stop_reply = true, .schema = "l0" }; cmd_parser = &cont_with_sig_cmd_desc; @@ -1785,6 +1802,7 @@ static int gdb_handle_packet(const char *line_buf) .handler = handle_step, .cmd = "s", .cmd_startswith = 1, + .allow_stop_reply = true, .schema = "L0" }; cmd_parser = &step_cmd_desc; @@ -1976,6 +1994,7 @@ void gdb_read_byte(uint8_t ch) { uint8_t reply; + gdbserver_state.allow_stop_reply = false; #ifndef CONFIG_USER_ONLY if (gdbserver_state.last_packet->len) { /* Waiting for a response to the last packet. If we see the start diff --git a/gdbstub/internals.h b/gdbstub/internals.h index 94ddff4495..33d21d6488 100644 --- a/gdbstub/internals.h +++ b/gdbstub/internals.h @@ -65,6 +65,11 @@ typedef struct GDBState { GByteArray *mem_buf; int sstep_flags; int supported_sstep_flags; + /* + * Whether we are allowed to send a stop reply packet at this moment. + * Must be set off after sending the stop reply itself. + */ + bool allow_stop_reply; } GDBState; /* lives in main gdbstub.c */ diff --git a/gdbstub/softmmu.c b/gdbstub/softmmu.c index 22ecd09d04..99d994e6bf 100644 --- a/gdbstub/softmmu.c +++ b/gdbstub/softmmu.c @@ -43,6 +43,7 @@ static void reset_gdbserver_state(void) g_free(gdbserver_state.processes); gdbserver_state.processes = NULL; gdbserver_state.process_num = 0; + gdbserver_state.allow_stop_reply = false; } /* @@ -139,6 +140,10 @@ static void gdb_vm_state_change(void *opaque, bool running, RunState state) return; } + if (!gdbserver_state.allow_stop_reply) { + return; + } + gdb_append_thread_id(cpu, tid); switch (state) { @@ -205,6 +210,7 @@ static void gdb_vm_state_change(void *opaque, bool running, RunState state) send_packet: gdb_put_packet(buf->str); + gdbserver_state.allow_stop_reply = false; /* disable single step if it was enabled */ cpu_single_step(cpu, 0); @@ -422,8 +428,11 @@ void gdb_exit(int code) trace_gdbstub_op_exiting((uint8_t)code); - snprintf(buf, sizeof(buf), "W%02x", (uint8_t)code); - gdb_put_packet(buf); + if (gdbserver_state.allow_stop_reply) { + snprintf(buf, sizeof(buf), "W%02x", (uint8_t)code); + gdb_put_packet(buf); + gdbserver_state.allow_stop_reply = false; + } qemu_chr_fe_deinit(&gdbserver_system_state.chr, true); } diff --git a/gdbstub/user.c b/gdbstub/user.c index 80488b6bb9..5b375be1d9 100644 --- a/gdbstub/user.c +++ b/gdbstub/user.c @@ -108,8 +108,11 @@ void gdb_exit(int code) trace_gdbstub_op_exiting((uint8_t)code); - snprintf(buf, sizeof(buf), "W%02x", (uint8_t)code); - gdb_put_packet(buf); + if (gdbserver_state.allow_stop_reply) { + snprintf(buf, sizeof(buf), "W%02x", (uint8_t)code); + gdb_put_packet(buf); + gdbserver_state.allow_stop_reply = false; + } } int gdb_handlesig(CPUState *cpu, int sig) @@ -127,11 +130,14 @@ int gdb_handlesig(CPUState *cpu, int sig) if (sig != 0) { gdb_set_stop_cpu(cpu); - g_string_printf(gdbserver_state.str_buf, - "T%02xthread:", gdb_target_signal_to_gdb(sig)); - gdb_append_thread_id(cpu, gdbserver_state.str_buf); - g_string_append_c(gdbserver_state.str_buf, ';'); - gdb_put_strbuf(); + if (gdbserver_state.allow_stop_reply) { + g_string_printf(gdbserver_state.str_buf, + "T%02xthread:", gdb_target_signal_to_gdb(sig)); + gdb_append_thread_id(cpu, gdbserver_state.str_buf); + g_string_append_c(gdbserver_state.str_buf, ';'); + gdb_put_strbuf(); + gdbserver_state.allow_stop_reply = false; + } } /* * gdb_put_packet() might have detected that the peer terminated the @@ -174,12 +180,14 @@ void gdb_signalled(CPUArchState *env, int sig) { char buf[4]; - if (!gdbserver_state.init || gdbserver_user_state.fd < 0) { + if (!gdbserver_state.init || gdbserver_user_state.fd < 0 || + !gdbserver_state.allow_stop_reply) { return; } snprintf(buf, sizeof(buf), "X%02x", gdb_target_signal_to_gdb(sig)); gdb_put_packet(buf); + gdbserver_state.allow_stop_reply = false; } static void gdb_accept_init(int fd)