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[2001:8b0:1d0::2]) by smtp.gmail.com with ESMTPSA id h10-20020a1ccc0a000000b0039763d41a48sm2507476wmb.25.2022.05.26.12.00.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 May 2022 12:00:56 -0700 (PDT) From: Peter Maydell To: qemu-devel@nongnu.org Cc: =?utf-8?q?Alex_Benn=C3=A9e?= , Richard Henderson , =?utf-8?q?Philippe_Mathie?= =?utf-8?q?u-Daud=C3=A9?= , Liviu Ionescu Subject: [PATCH 1/2] gdbstub: Don't use GDB syscalls if no GDB is attached Date: Thu, 26 May 2022 20:00:52 +0100 Message-Id: <20220526190053.521505-2-peter.maydell@linaro.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220526190053.521505-1-peter.maydell@linaro.org> References: <20220526190053.521505-1-peter.maydell@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::329; envelope-from=peter.maydell@linaro.org; helo=mail-wm1-x329.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, RCVD_IN_DNSWL_NONE=-0.0001, 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+patch=linaro.org@nongnu.org Sender: "Qemu-devel" In two places in gdbstub.c we look at gdbserver_state.init to decide whether we're going to do a semihosting syscall via the gdb remote protocol: * when setting up, if the user didn't explicitly select either native semihosting or gdb semihosting, we autoselect, with the intended behaviour "use gdb if gdb is connected" * when the semihosting layer attempts to do a syscall via gdb, we silently ignore it if the gdbstub wasn't actually set up However, if the user's commandline sets up the gdbstub but tells QEMU to start rather than waiting for a GDB to connect (eg using '-s' but not '-S'), then we will have gdbserver_state.init true but no actual connection; an attempt to use gdb syscalls will then crash because we try to use gdbserver_state.c_cpu when it hasn't been set up: #0 0x00007ffff6803ba8 in qemu_cpu_kick (cpu=0x0) at ../../softmmu/cpus.c:457 #1 0x00007ffff6c03913 in gdb_do_syscallv (cb=0x7ffff6c19944 , fmt=0x7ffff7573b7e "", va=0x7ffff56294c0) at ../../gdbstub.c:2946 #2 0x00007ffff6c19c3a in common_semi_gdb_syscall (cs=0x7ffff83fe060, cb=0x7ffff6c19944 , fmt=0x7ffff7573b75 "isatty,%x") at ../../semihosting/arm-compat-semi.c:494 #3 0x00007ffff6c1a064 in gdb_isattyfn (cs=0x7ffff83fe060, gf=0x7ffff86a3690) at ../../semihosting/arm-compat-semi.c:636 #4 0x00007ffff6c1b20f in do_common_semihosting (cs=0x7ffff83fe060) at ../../semihosting/arm-compat-semi.c:967 #5 0x00007ffff693a037 in handle_semihosting (cs=0x7ffff83fe060) at ../../target/arm/helper.c:10316 You can probably also get into this state via some odd corner cases involving connecting a GDB and then telling it to detach from all the vCPUs. Abstract out the test into a new gdb_attached() function which returns true only if there's actually a GDB connected to the debug stub and attached to at least one vCPU. Reported-by: Liviu Ionescu Signed-off-by: Peter Maydell Reviewed-by: Philippe Mathieu-Daudé Reviewed-by: Luc Michel --- Silently doing nothing in gdb_do_syscallv(), never calling the callback function, is kind of dodgy. But it's what the code is doing already, and besides it's not clear what we should do if the user specifically says "semihosting calls via the gdb stub" and then doesn't connect gdb... --- gdbstub.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/gdbstub.c b/gdbstub.c index a3ff8702cef..88a34c8f522 100644 --- a/gdbstub.c +++ b/gdbstub.c @@ -443,6 +443,15 @@ static int get_char(void) } #endif +/* + * Return true if there is a GDB currently connected to the stub + * and attached to a CPU + */ +static bool gdb_attached(void) +{ + return gdbserver_state.init && gdbserver_state.c_cpu; +} + static enum { GDB_SYS_UNKNOWN, GDB_SYS_ENABLED, @@ -464,8 +473,7 @@ int use_gdb_syscalls(void) /* -semihosting-config target=auto */ /* On the first call check if gdb is connected and remember. */ if (gdb_syscall_mode == GDB_SYS_UNKNOWN) { - gdb_syscall_mode = gdbserver_state.init ? - GDB_SYS_ENABLED : GDB_SYS_DISABLED; + gdb_syscall_mode = gdb_attached() ? GDB_SYS_ENABLED : GDB_SYS_DISABLED; } return gdb_syscall_mode == GDB_SYS_ENABLED; } @@ -2886,7 +2894,7 @@ void gdb_do_syscallv(gdb_syscall_complete_cb cb, const char *fmt, va_list va) target_ulong addr; uint64_t i64; - if (!gdbserver_state.init) { + if (!gdb_attached()) { return; }