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Thu, 01 Feb 2024 09:15:11 -0800 (PST) Received: from draig (localhost [IPv6:::1]) by draig.lan (Postfix) with ESMTP id BC2D75F7AF; Thu, 1 Feb 2024 17:15:10 +0000 (GMT) From: =?utf-8?Q?Alex_Benn=C3=A9e?= To: Ilya Leoshkevich Cc: Riku Voipio , Philippe =?utf-8?Q?Mathieu-Daud?= =?utf-8?Q?=C3=A9?= , qemu-devel@nongnu.org Subject: Re: [PATCH v2 1/2] gdbstub: Implement catching syscalls In-Reply-To: <20240116094411.216665-2-iii@linux.ibm.com> (Ilya Leoshkevich's message of "Tue, 16 Jan 2024 10:41:53 +0100") References: <20240116094411.216665-1-iii@linux.ibm.com> <20240116094411.216665-2-iii@linux.ibm.com> User-Agent: mu4e 1.11.27; emacs 29.1 Date: Thu, 01 Feb 2024 17:15:10 +0000 Message-ID: <8734uckswx.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::42c; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x42c.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Ilya Leoshkevich writes: > GDB supports stopping on syscall entry and exit using the "catch > syscall" command. It relies on 3 packets, which are currently not > supported by QEMU: > > * qSupported:QCatchSyscalls+ [1] > * QCatchSyscalls: [2] > * T05syscall_entry: and T05syscall_return: [3] > > Implement generation and handling of these packets. > > [1] https://sourceware.org/gdb/current/onlinedocs/gdb.html/General-Query-= Packets.html#qSupported > [2] https://sourceware.org/gdb/current/onlinedocs/gdb.html/General-Query-= Packets.html#QCatchSyscalls > [3] https://sourceware.org/gdb/current/onlinedocs/gdb.html/Stop-Reply-Pac= kets.html > > Signed-off-by: Ilya Leoshkevich > --- > gdbstub/gdbstub.c | 9 +++ > gdbstub/internals.h | 2 + > gdbstub/user-target.c | 5 ++ > gdbstub/user.c | 104 ++++++++++++++++++++++++++++++++++- > include/gdbstub/user.h | 29 +++++++++- > include/user/syscall-trace.h | 7 ++- > 6 files changed, 151 insertions(+), 5 deletions(-) > > diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c > index 46d752bbc2c..7e73e916bdc 100644 > --- a/gdbstub/gdbstub.c > +++ b/gdbstub/gdbstub.c > @@ -1617,6 +1617,7 @@ static void handle_query_supported(GArray *params, = void *user_ctx) > if (gdbserver_state.c_cpu->opaque) { > g_string_append(gdbserver_state.str_buf, ";qXfer:auxv:read+"); > } > + g_string_append(gdbserver_state.str_buf, ";QCatchSyscalls+"); > #endif > g_string_append(gdbserver_state.str_buf, ";qXfer:exec-file:read+"); > #endif > @@ -1810,6 +1811,14 @@ static const GdbCmdParseEntry gdb_gen_set_table[] = =3D { > .schema =3D "l0" > }, > #endif > +#if defined(CONFIG_USER_ONLY) > + { > + .handler =3D gdb_handle_set_catch_syscalls, > + .cmd =3D "CatchSyscalls:", > + .cmd_startswith =3D 1, > + .schema =3D "s0", > + }, > +#endif > }; >=20=20 > static void handle_gen_query(GArray *params, void *user_ctx) > diff --git a/gdbstub/internals.h b/gdbstub/internals.h > index 5c0c725e54c..56b7c13b750 100644 > --- a/gdbstub/internals.h > +++ b/gdbstub/internals.h > @@ -136,6 +136,7 @@ void gdb_append_thread_id(CPUState *cpu, GString *buf= ); > int gdb_get_cpu_index(CPUState *cpu); > unsigned int gdb_get_max_cpus(void); /* both */ > bool gdb_can_reverse(void); /* softmmu, stub for user */ > +int gdb_target_sigtrap(void); /* user */ >=20=20 > void gdb_create_default_process(GDBState *s); >=20=20 > @@ -194,6 +195,7 @@ void gdb_handle_v_file_close(GArray *params, void *us= er_ctx); /* user */ > void gdb_handle_v_file_pread(GArray *params, void *user_ctx); /* user */ > void gdb_handle_v_file_readlink(GArray *params, void *user_ctx); /* user= */ > void gdb_handle_query_xfer_exec_file(GArray *params, void *user_ctx); /*= user */ > +void gdb_handle_set_catch_syscalls(GArray *params, void *user_ctx); /* u= ser */ >=20=20 > void gdb_handle_query_attached(GArray *params, void *user_ctx); /* both = */ >=20=20 > diff --git a/gdbstub/user-target.c b/gdbstub/user-target.c > index c4bba4c72c7..b7d4c37cd81 100644 > --- a/gdbstub/user-target.c > +++ b/gdbstub/user-target.c > @@ -418,3 +418,8 @@ void gdb_handle_query_xfer_exec_file(GArray *params, = void *user_ctx) > ts->bprm->filename + offset); > gdb_put_strbuf(); > } > + > +int gdb_target_sigtrap(void) > +{ > + return TARGET_SIGTRAP; > +} > diff --git a/gdbstub/user.c b/gdbstub/user.c > index dbe1d9b8875..01dd7169258 100644 > --- a/gdbstub/user.c > +++ b/gdbstub/user.c > @@ -10,6 +10,7 @@ > */ >=20=20 > #include "qemu/osdep.h" > +#include "qemu/bitops.h" > #include "qemu/cutils.h" > #include "qemu/sockets.h" > #include "exec/hwaddr.h" > @@ -21,11 +22,25 @@ > #include "trace.h" > #include "internals.h" >=20=20 > +enum GDBCatchSyscallsState { > + GDB_CATCH_SYSCALLS_NONE, > + GDB_CATCH_SYSCALLS_ALL, > + GDB_CATCH_SYSCALLS_SELECTED, > +}; > +#define GDB_NR_SYSCALLS 1024 > +typedef unsigned long GDBSyscallsMask[BITS_TO_LONGS(GDB_NR_SYSCALLS)]; > + > /* User-mode specific state */ > typedef struct { > int fd; > char *socket_path; > int running_state; > + /* > + * Store syscalls mask without memory allocation in order to avoid > + * implementing synchronization. > + */ > + enum GDBCatchSyscallsState catch_syscalls_state; > + GDBSyscallsMask catch_syscalls_mask; > } GDBUserState; >=20=20 > static GDBUserState gdbserver_user_state; > @@ -121,7 +136,7 @@ void gdb_qemu_exit(int code) > exit(code); > } >=20=20 > -int gdb_handlesig(CPUState *cpu, int sig) > +int gdb_handlesig_reason(CPUState *cpu, int sig, const char *reason) > { > char buf[256]; > int n; > @@ -141,6 +156,9 @@ int gdb_handlesig(CPUState *cpu, int sig) > "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, ';'); > + if (reason) { > + g_string_append(gdbserver_state.str_buf, reason); > + } > gdb_put_strbuf(); > gdbserver_state.allow_stop_reply =3D false; > } > @@ -499,3 +517,87 @@ void gdb_syscall_handling(const char *syscall_packet) > gdb_put_packet(syscall_packet); > gdb_handlesig(gdbserver_state.c_cpu, 0); > } > + > +static bool should_catch_syscall(int num) > +{ > + switch (gdbserver_user_state.catch_syscalls_state) { > + case GDB_CATCH_SYSCALLS_NONE: > + return false; > + case GDB_CATCH_SYSCALLS_ALL: > + return true; > + case GDB_CATCH_SYSCALLS_SELECTED: > + if (num < 0 || num >=3D GDB_NR_SYSCALLS) { > + return false; > + } else { > + return test_bit(num, gdbserver_user_state.catch_syscalls_mas= k); > + } > + default: > + g_assert_not_reached(); > + } > +} > + > +void gdb_syscall_entry(CPUState *cs, int num) > +{ > + char reason[32]; > + > + if (should_catch_syscall(num)) { > + snprintf(reason, sizeof(reason), "syscall_entry:%x;", num); > + gdb_handlesig_reason(cs, gdb_target_sigtrap(), reason); > + } > +} > + > +void gdb_syscall_return(CPUState *cs, int num) > +{ > + char reason[32]; > + > + if (should_catch_syscall(num)) { > + snprintf(reason, sizeof(reason), "syscall_return:%x;", num); > + gdb_handlesig_reason(cs, gdb_target_sigtrap(), reason); > + } > +} I'm not super keen on re-introducing snprintf's as we've been slowly eradicating them from the code base. How about: g_autoptr(GString) reason =3D g_string_printf("syscall_return:%x;", num= ); gdb_handlesig_reason(cs, gdb_target_sigtrap(), reason); > + > +void gdb_handle_set_catch_syscalls(GArray *params, void *user_ctx) > +{ > + enum GDBCatchSyscallsState catch_syscalls_state; > + const char *param =3D get_param(params, 0)->data; > + GDBSyscallsMask catch_syscalls_mask; > + bool catch_syscalls_none; > + unsigned int num; > + const char *p; > + Perhaps a little comment: /* terminating with 0/1 to disable/enable all */ > + catch_syscalls_none =3D strcmp(param, "0") =3D=3D 0; > + if (catch_syscalls_none || strcmp(param, "1") =3D=3D 0) { > + gdbserver_user_state.catch_syscalls_state =3D > + catch_syscalls_none ? GDB_CATCH_SYSCALLS_NONE : > + GDB_CATCH_SYSCALLS_ALL; > + gdb_put_packet("OK"); > + return; > + } /* otherwise decode the following list of syscalls... */ ? > + if (param[0] =3D=3D '1' && param[1] =3D=3D ';') { > + catch_syscalls_state =3D GDB_CATCH_SYSCALLS_SELECTED; > + memset(catch_syscalls_mask, 0, sizeof(catch_syscalls_mask)); > + for (p =3D ¶m[2];; p++) { > + if (qemu_strtoui(p, &p, 16, &num) || (*p && *p !=3D ';')) { > + goto err; > + } > + if (num >=3D GDB_NR_SYSCALLS) { > + /* Fall back to reporting all syscalls. */ > + catch_syscalls_state =3D GDB_CATCH_SYSCALLS_ALL; Is this the right thing or maybe we should error because gdb sent us something strange? In fact you could do: if (qemu_strtoui(p, &p, 16, &num) || (*p && *p !=3D ';') || num >=3D GDB_NR_SYSCALLS) { gdb_put_packet("E00"); return; } and skip the goto err > + } else { > + set_bit(num, catch_syscalls_mask); > + } > + if (!*p) { > + break; > + } Could this be in the for loop? for(p =3D ¶m[2]; *p; p++) =20=20 > + } > + gdbserver_user_state.catch_syscalls_state =3D catch_syscalls_sta= te; > + memcpy(gdbserver_user_state.catch_syscalls_mask, catch_syscalls_= mask, > + sizeof(catch_syscalls_mask)); > + gdb_put_packet("OK"); > + return; > + } > + > +err: > + gdb_put_packet("E00"); > +} > diff --git a/include/gdbstub/user.h b/include/gdbstub/user.h > index d392e510c59..68b6534130c 100644 > --- a/include/gdbstub/user.h > +++ b/include/gdbstub/user.h > @@ -10,9 +10,10 @@ > #define GDBSTUB_USER_H >=20=20 > /** > - * gdb_handlesig() - yield control to gdb > + * gdb_handlesig_reason() - yield control to gdb > * @cpu: CPU > * @sig: if non-zero, the signal number which caused us to stop > + * @reason: stop reason for stop reply packet or NULL > * > * This function yields control to gdb, when a user-mode-only target > * needs to stop execution. If @sig is non-zero, then we will send a > @@ -24,7 +25,18 @@ > * or 0 if no signal should be delivered, ie the signal that caused > * us to stop should be ignored. > */ > -int gdb_handlesig(CPUState *, int); > +int gdb_handlesig_reason(CPUState *, int, const char *); > + > +/** > + * gdb_handlesig() - yield control to gdb > + * @cpu CPU > + * @sig: if non-zero, the signal number which caused us to stop > + * @see gdb_handlesig_reason() > + */ > +static inline int gdb_handlesig(CPUState *cpu, int sig) > +{ > + return gdb_handlesig_reason(cpu, sig, NULL); > +} >=20=20 > /** > * gdb_signalled() - inform remote gdb of sig exit > @@ -39,5 +51,18 @@ void gdb_signalled(CPUArchState *as, int sig); > */ > void gdbserver_fork(CPUState *cs); >=20=20 > +/** > + * gdb_syscall_entry() - inform gdb of syscall entry and yield control t= o it > + * @cs: CPU > + * @num: syscall number > + */ > +void gdb_syscall_entry(CPUState *cs, int num); > + > +/** > + * gdb_syscall_entry() - inform gdb of syscall return and yield control = to it > + * @cs: CPU > + * @num: syscall number > + */ > +void gdb_syscall_return(CPUState *cs, int num); >=20=20 > #endif /* GDBSTUB_USER_H */ > diff --git a/include/user/syscall-trace.h b/include/user/syscall-trace.h > index 557f881a79b..b48b2b2d0ae 100644 > --- a/include/user/syscall-trace.h > +++ b/include/user/syscall-trace.h > @@ -11,6 +11,7 @@ > #define SYSCALL_TRACE_H >=20=20 > #include "exec/user/abitypes.h" > +#include "gdbstub/user.h" > #include "qemu/plugin.h" > #include "trace/trace-root.h" >=20=20 > @@ -20,7 +21,7 @@ > * could potentially unify the -strace code here as well. > */ >=20=20 > -static inline void record_syscall_start(void *cpu, int num, > +static inline void record_syscall_start(CPUState *cpu, int num, > abi_long arg1, abi_long arg2, > abi_long arg3, abi_long arg4, > abi_long arg5, abi_long arg6, > @@ -29,11 +30,13 @@ static inline void record_syscall_start(void *cpu, in= t num, > qemu_plugin_vcpu_syscall(cpu, num, > arg1, arg2, arg3, arg4, > arg5, arg6, arg7, arg8); > + gdb_syscall_entry(cpu, num); > } >=20=20 > -static inline void record_syscall_return(void *cpu, int num, abi_long re= t) > +static inline void record_syscall_return(CPUState *cpu, int num, abi_lon= g ret) > { > qemu_plugin_vcpu_syscall_ret(cpu, num, ret); > + gdb_syscall_return(cpu, num); This clean-up belongs in a separate patch. > } --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro