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Mon, 2 Nov 2020 16:13:46 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 34jf46qwte-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 02 Nov 2020 16:13:46 +0000 Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0A2GDjYg015953; Mon, 2 Nov 2020 16:13:45 GMT Received: from ca-dev63.us.oracle.com (/10.211.8.221) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 02 Nov 2020 08:13:45 -0800 From: Steve Sistare To: qemu-devel@nongnu.org Subject: [PATCH V2] vl: pause option Date: Mon, 2 Nov 2020 07:50:03 -0800 Message-Id: <1604332203-435466-1-git-send-email-steven.sistare@oracle.com> X-Mailer: git-send-email 1.8.3.1 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9793 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=1 mlxscore=0 bulkscore=0 malwarescore=0 mlxlogscore=954 phishscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011020125 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9793 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=1 impostorscore=0 malwarescore=0 priorityscore=1501 mlxlogscore=971 bulkscore=0 phishscore=0 adultscore=0 mlxscore=0 lowpriorityscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011020125 Received-SPF: pass client-ip=141.146.126.78; 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Berrange" , "Dr. David Alan Gilbert" , Steve Sistare Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Provide the -pause command-line parameter and the QEMU_PAUSE environment variable to pause QEMU during process startup using SIGSTOP and allow a developer to attach a debugger, or observe the process using tools such as strace. Useful when the QEMU has been launched with some other entity, such as libvirt. QEMU_PAUSE is checked in a constructor at the highest priority, and can be used to debug other constructors. The -pause option is checked later, during argument processing in main, but is useful if passing an environment variable from a launcher to qemu is awkard. Usage: qemu -pause, or QEMU_PAUSE=1 After attaching a debugger, send SIGCONT to the qemu process to continue. Example: $ QEMU_PAUSE=1 qemu-system-x86_64 ... QEMU pid 18371 is stopped. [1]+ Stopped $ gdb -p 18371 (gdb) $ kill -cont 18371 (gdb) break rcu_init (gdb) continue Program received signal SIGCONT, Continued. (gdb) continue Breakpoint 1, rcu_init () at util/rcu.c:380 Thanks to Daniel P. Berrange for suggesting SIGSTOP. Signed-off-by: Steve Sistare --- qemu-options.hx | 14 ++++++++++++++ softmmu/vl.c | 23 +++++++++++++++++++++++ 2 files changed, 37 insertions(+) diff --git a/qemu-options.hx b/qemu-options.hx index 708583b..42edd70 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -3668,6 +3668,20 @@ SRST option is experimental. ERST +DEF("pause", 0, QEMU_OPTION_pause, \ + "-pause pause the qemu process in main using SIGSTOP.\n" + " to pause earlier, before constructors are run, set the\n" + " environment variable QEMU_PAUSE=1 before starting qemu.\n", + QEMU_ARCH_ALL) + +SRST +``-pause`` + Pause the qemu process in main using SIGSTOP. This is useful for attaching + a debugger after QEMU has been launched by some other entity. After + attaching, send SIGCONT to continue. To pause earlier, before constructors + are run, set the environment variable QEMU_PAUSE=1 before starting qemu. +ERST + DEF("S", 0, QEMU_OPTION_S, \ "-S freeze CPU at startup (use 'c' to start execution)\n", QEMU_ARCH_ALL) diff --git a/softmmu/vl.c b/softmmu/vl.c index 4eb9d1f..aee1a96 100644 --- a/softmmu/vl.c +++ b/softmmu/vl.c @@ -2829,6 +2829,24 @@ static void create_default_memdev(MachineState *ms, const char *path) &error_fatal); } +static __attribute__((constructor(101))) void maybe_pause(void) +{ + const char *pause = getenv("QEMU_PAUSE"); + + if (pause) { + if (!pause[0] || !strcmp(pause, "1")) { + printf("QEMU pid %d is stopped. Send SIGCONT to continue.\n", + getpid()); + kill(getpid(), SIGSTOP); + } else if (strcmp(pause, "0")) { + fprintf(stderr, "error: QEMU_PAUSE bad value %s. Must be 1 or " + "empty to enable, 0 or unset to disable.\n", + pause); + exit(1); + } + } +} + void qemu_init(int argc, char **argv, char **envp) { int i; @@ -3191,6 +3209,11 @@ void qemu_init(int argc, char **argv, char **envp) case QEMU_OPTION_gdb: add_device_config(DEV_GDB, optarg); break; + case QEMU_OPTION_pause: + printf("QEMU pid %d is stopped. Send SIGCONT to continue.\n", + getpid()); + kill(getpid(), SIGSTOP); + break; case QEMU_OPTION_L: if (is_help_option(optarg)) { list_data_dirs = true;