debuggerd/debuggerd.cpp - platform/system/core - Gitiles

 /*
  * Copyright 2006, The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include <stdio.h>
 #include <errno.h>
 #include <signal.h>
 #include <pthread.h>
 #include <stdarg.h>
 #include <fcntl.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <time.h>

 #include <sys/ptrace.h>
 #include <sys/wait.h>
 #include <elf.h>
 #include <sys/stat.h>
 #include <sys/poll.h>

 #include <selinux/android.h>

 #include <log/logger.h>

 #include <cutils/sockets.h>
 #include <cutils/properties.h>
 #include <cutils/debugger.h>

 #include <linux/input.h>

 #include <private/android_filesystem_config.h>

 #include "backtrace.h"
 #include "getevent.h"
 #include "tombstone.h"
 #include "utility.h"

 struct debugger_request_t {
   debugger_action_t action;
   pid_t pid, tid;
   uid_t uid, gid;
   uintptr_t abort_msg_address;
   int32_t original_si_code;
 };

 static void wait_for_user_action(const debugger_request_t &request) {
   // Find out the name of the process that crashed.
   char path[64];
   snprintf(path, sizeof(path), "/proc/%d/exe", request.pid);

   char exe[PATH_MAX];
   int count;
   if ((count = readlink(path, exe, sizeof(exe) - 1)) == -1) {
     ALOGE("readlink('%s') failed: %s", path, strerror(errno));
     strlcpy(exe, "unknown", sizeof(exe));
   } else {
     exe[count] = '\0';
   }

   // Explain how to attach the debugger.
   ALOGI("********************************************************\n"
         "* Process %d has been suspended while crashing.\n"
         "* To attach gdbserver for a gdb connection on port 5039\n"
         "* and start gdbclient:\n"
         "*\n"
         "*     gdbclient %s :5039 %d\n"
         "*\n"
         "* Wait for gdb to start, then press the VOLUME DOWN key\n"
         "* to let the process continue crashing.\n"
         "********************************************************",
         request.pid, exe, request.tid);

   // Wait for VOLUME DOWN.
   if (init_getevent() == 0) {
     while (true) {
       input_event e;
       if (get_event(&e, -1) == 0) {
         if (e.type == EV_KEY && e.code == KEY_VOLUMEDOWN && e.value == 0) {
           break;
         }
       }
     }
     uninit_getevent();
   }

   ALOGI("debuggerd resuming process %d", request.pid);
 }

 static int get_process_info(pid_t tid, pid_t* out_pid, uid_t* out_uid, uid_t* out_gid) {
   char path[64];
   snprintf(path, sizeof(path), "/proc/%d/status", tid);

   FILE* fp = fopen(path, "r");
   if (!fp) {
     return -1;
   }

   int fields = 0;
   char line[1024];
   while (fgets(line, sizeof(line), fp)) {
     size_t len = strlen(line);
     if (len > 6 && !memcmp(line, "Tgid:\t", 6)) {
       *out_pid = atoi(line + 6);
       fields |= 1;
     } else if (len > 5 && !memcmp(line, "Uid:\t", 5)) {
       *out_uid = atoi(line + 5);
       fields |= 2;
     } else if (len > 5 && !memcmp(line, "Gid:\t", 5)) {
       *out_gid = atoi(line + 5);
       fields |= 4;
     }
   }
   fclose(fp);
   return fields == 7 ? 0 : -1;
 }

 static int selinux_enabled;

 /*
  * Corresponds with debugger_action_t enum type in
  * include/cutils/debugger.h.
  */
 static const char *debuggerd_perms[] = {
   NULL, /* crash is only used on self, no check applied */
   "dump_tombstone",
   "dump_backtrace"
 };

 static bool selinux_action_allowed(int s, pid_t tid, debugger_action_t action)
 {
   char *scon = NULL, *tcon = NULL;
   const char *tclass = "debuggerd";
   const char *perm;
   bool allowed = false;

   if (selinux_enabled <= 0)
     return true;

   if (action <= 0 || action >= (sizeof(debuggerd_perms)/sizeof(debuggerd_perms[0]))) {
     ALOGE("SELinux:  No permission defined for debugger action %d", action);
     return false;
   }

   perm = debuggerd_perms[action];

   if (getpeercon(s, &scon) < 0) {
     ALOGE("Cannot get peer context from socket\n");
     goto out;
   }

   if (getpidcon(tid, &tcon) < 0) {
     ALOGE("Cannot get context for tid %d\n", tid);
     goto out;
   }

   allowed = (selinux_check_access(scon, tcon, tclass, perm, NULL) == 0);

 out:
    freecon(scon);
    freecon(tcon);
    return allowed;
 }

 static int read_request(int fd, debugger_request_t* out_request) {
   ucred cr;
   socklen_t len = sizeof(cr);
   int status = getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
   if (status != 0) {
     ALOGE("cannot get credentials");
     return -1;
   }

   ALOGV("reading tid");
   fcntl(fd, F_SETFL, O_NONBLOCK);

   pollfd pollfds[1];
   pollfds[0].fd = fd;
   pollfds[0].events = POLLIN;
   pollfds[0].revents = 0;
   status = TEMP_FAILURE_RETRY(poll(pollfds, 1, 3000));
   if (status != 1) {
     ALOGE("timed out reading tid (from pid=%d uid=%d)\n", cr.pid, cr.uid);
     return -1;
   }

   debugger_msg_t msg;
   memset(&msg, 0, sizeof(msg));
   status = TEMP_FAILURE_RETRY(read(fd, &msg, sizeof(msg)));
   if (status < 0) {
     ALOGE("read failure? %s (pid=%d uid=%d)\n", strerror(errno), cr.pid, cr.uid);
     return -1;
   }
   if (status != sizeof(debugger_msg_t)) {
     ALOGE("invalid crash request of size %d (from pid=%d uid=%d)\n", status, cr.pid, cr.uid);
     return -1;
   }

   out_request->action = msg.action;
   out_request->tid = msg.tid;
   out_request->pid = cr.pid;
   out_request->uid = cr.uid;
   out_request->gid = cr.gid;
   out_request->abort_msg_address = msg.abort_msg_address;
   out_request->original_si_code = msg.original_si_code;

   if (msg.action == DEBUGGER_ACTION_CRASH) {
     // Ensure that the tid reported by the crashing process is valid.
     char buf[64];
     struct stat s;
     snprintf(buf, sizeof buf, "/proc/%d/task/%d", out_request->pid, out_request->tid);
     if (stat(buf, &s)) {
       ALOGE("tid %d does not exist in pid %d. ignoring debug request\n",
           out_request->tid, out_request->pid);
       return -1;
     }
   } else if (cr.uid == 0
             || (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
     // Only root or system can ask us to attach to any process and dump it explicitly.
     // However, system is only allowed to collect backtraces but cannot dump tombstones.
     status = get_process_info(out_request->tid, &out_request->pid,
                               &out_request->uid, &out_request->gid);
     if (status < 0) {
       ALOGE("tid %d does not exist. ignoring explicit dump request\n", out_request->tid);
       return -1;
     }

     if (!selinux_action_allowed(fd, out_request->tid, out_request->action))
       return -1;
   } else {
     // No one else is allowed to dump arbitrary processes.
     return -1;
   }
   return 0;
 }

 static bool should_attach_gdb(debugger_request_t* request) {
   if (request->action == DEBUGGER_ACTION_CRASH) {
     char value[PROPERTY_VALUE_MAX];
     property_get("debug.db.uid", value, "-1");
     int debug_uid = atoi(value);
     return debug_uid >= 0 && request->uid <= (uid_t)debug_uid;
   }
   return false;
 }

 static void handle_request(int fd) {
   ALOGV("handle_request(%d)\n", fd);

   debugger_request_t request;
   memset(&request, 0, sizeof(request));
   int status = read_request(fd, &request);
   if (!status) {
     ALOGV("BOOM: pid=%d uid=%d gid=%d tid=%d\n",
          request.pid, request.uid, request.gid, request.tid);

     // At this point, the thread that made the request is blocked in
     // a read() call.  If the thread has crashed, then this gives us
     // time to PTRACE_ATTACH to it before it has a chance to really fault.
     //
     // The PTRACE_ATTACH sends a SIGSTOP to the target process, but it
     // won't necessarily have stopped by the time ptrace() returns.  (We
     // currently assume it does.)  We write to the file descriptor to
     // ensure that it can run as soon as we call PTRACE_CONT below.
     // See details in bionic/libc/linker/debugger.c, in function
     // debugger_signal_handler().
     if (ptrace(PTRACE_ATTACH, request.tid, 0, 0)) {
       ALOGE("ptrace attach failed: %s\n", strerror(errno));
     } else {
       bool detach_failed = false;
       bool tid_unresponsive = false;
       bool attach_gdb = should_attach_gdb(&request);
       if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
         ALOGE("failed responding to client: %s\n", strerror(errno));
       } else {
         char* tombstone_path = NULL;

         if (request.action == DEBUGGER_ACTION_CRASH) {
           close(fd);
           fd = -1;
         }

         int total_sleep_time_usec = 0;
         for (;;) {
           int signal = wait_for_sigstop(request.tid, &total_sleep_time_usec, &detach_failed);
           if (signal == -1) {
             tid_unresponsive = true;
             break;
           }

           switch (signal) {
             case SIGSTOP:
               if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
                 ALOGV("stopped -- dumping to tombstone\n");
                 tombstone_path = engrave_tombstone(request.pid, request.tid,
                                                    signal, request.original_si_code,
                                                    request.abort_msg_address, true,
                                                    &detach_failed, &total_sleep_time_usec);
               } else if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE) {
                 ALOGV("stopped -- dumping to fd\n");
                 dump_backtrace(fd, -1, request.pid, request.tid, &detach_failed,
                                &total_sleep_time_usec);
               } else {
                 ALOGV("stopped -- continuing\n");
                 status = ptrace(PTRACE_CONT, request.tid, 0, 0);
                 if (status) {
                   ALOGE("ptrace continue failed: %s\n", strerror(errno));
                 }
                 continue; // loop again
               }
               break;

             case SIGABRT:
             case SIGBUS:
             case SIGFPE:
             case SIGILL:
             case SIGPIPE:
             case SIGSEGV:
 #ifdef SIGSTKFLT
             case SIGSTKFLT:
 #endif
             case SIGTRAP:
               ALOGV("stopped -- fatal signal\n");
               // Send a SIGSTOP to the process to make all of
               // the non-signaled threads stop moving.  Without
               // this we get a lot of "ptrace detach failed:
               // No such process".
               kill(request.pid, SIGSTOP);
               // don't dump sibling threads when attaching to GDB because it
               // makes the process less reliable, apparently...
               tombstone_path = engrave_tombstone(request.pid, request.tid,
                                                  signal, request.original_si_code,
                                                  request.abort_msg_address, !attach_gdb,
                                                  &detach_failed, &total_sleep_time_usec);
               break;

             default:
               ALOGE("process stopped due to unexpected signal %d\n", signal);
               break;
           }
           break;
         }

         if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
           if (tombstone_path) {
             write(fd, tombstone_path, strlen(tombstone_path));
           }
           close(fd);
           fd = -1;
         }
         free(tombstone_path);
       }

       if (!tid_unresponsive) {
         ALOGV("detaching");
         if (attach_gdb) {
           // stop the process so we can debug
           kill(request.pid, SIGSTOP);
         }
         if (ptrace(PTRACE_DETACH, request.tid, 0, 0)) {
           ALOGE("ptrace detach from %d failed: %s", request.tid, strerror(errno));
           detach_failed = true;
         } else if (attach_gdb) {
           // if debug.db.uid is set, its value indicates if we should wait
           // for user action for the crashing process.
           // in this case, we log a message and turn the debug LED on
           // waiting for a gdb connection (for instance)
           wait_for_user_action(request);
         }
       }

       // resume stopped process (so it can crash in peace).
       kill(request.pid, SIGCONT);

       // If we didn't successfully detach, we're still the parent, and the
       // actual parent won't receive a death notification via wait(2).  At this point
       // there's not much we can do about that.
       if (detach_failed) {
         ALOGE("debuggerd committing suicide to free the zombie!\n");
         kill(getpid(), SIGKILL);
       }
     }

   }
   if (fd >= 0) {
     close(fd);
   }
 }

 static int do_server() {
   // debuggerd crashes can't be reported to debuggerd.
   // Reset all of the crash handlers.
   signal(SIGABRT, SIG_DFL);
   signal(SIGBUS, SIG_DFL);
   signal(SIGFPE, SIG_DFL);
   signal(SIGILL, SIG_DFL);
   signal(SIGSEGV, SIG_DFL);
 #ifdef SIGSTKFLT
   signal(SIGSTKFLT, SIG_DFL);
 #endif
   signal(SIGTRAP, SIG_DFL);

   // Ignore failed writes to closed sockets
   signal(SIGPIPE, SIG_IGN);

   int logsocket = socket_local_client("logd", ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_DGRAM);
   if (logsocket < 0) {
     logsocket = -1;
   } else {
     fcntl(logsocket, F_SETFD, FD_CLOEXEC);
   }

   struct sigaction act;
   act.sa_handler = SIG_DFL;
   sigemptyset(&act.sa_mask);
   sigaddset(&act.sa_mask,SIGCHLD);
   act.sa_flags = SA_NOCLDWAIT;
   sigaction(SIGCHLD, &act, 0);

   int s = socket_local_server(DEBUGGER_SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_STREAM);
   if (s < 0)
     return 1;
   fcntl(s, F_SETFD, FD_CLOEXEC);

   ALOGI("debuggerd: " __DATE__ " " __TIME__ "\n");

   for (;;) {
     sockaddr addr;
     socklen_t alen = sizeof(addr);

     ALOGV("waiting for connection\n");
     int fd = accept(s, &addr, &alen);
     if (fd < 0) {
       ALOGV("accept failed: %s\n", strerror(errno));
       continue;
     }

     fcntl(fd, F_SETFD, FD_CLOEXEC);

     handle_request(fd);
   }
   return 0;
 }

 static int do_explicit_dump(pid_t tid, bool dump_backtrace) {
   fprintf(stdout, "Sending request to dump task %d.\n", tid);

   if (dump_backtrace) {
     fflush(stdout);
     if (dump_backtrace_to_file(tid, fileno(stdout)) < 0) {
       fputs("Error dumping backtrace.\n", stderr);
       return 1;
     }
   } else {
     char tombstone_path[PATH_MAX];
     if (dump_tombstone(tid, tombstone_path, sizeof(tombstone_path)) < 0) {
       fputs("Error dumping tombstone.\n", stderr);
       return 1;
     }
     fprintf(stderr, "Tombstone written to: %s\n", tombstone_path);
   }
   return 0;
 }

 static void usage() {
   fputs("Usage: -b [<tid>]\n"
         "  -b dump backtrace to console, otherwise dump full tombstone file\n"
         "\n"
         "If tid specified, sends a request to debuggerd to dump that task.\n"
         "Otherwise, starts the debuggerd server.\n", stderr);
 }

 int main(int argc, char** argv) {
   union selinux_callback cb;
   if (argc == 1) {
     selinux_enabled = is_selinux_enabled();
     cb.func_log = selinux_log_callback;
     selinux_set_callback(SELINUX_CB_LOG, cb);
     return do_server();
   }

   bool dump_backtrace = false;
   bool have_tid = false;
   pid_t tid = 0;
   for (int i = 1; i < argc; i++) {
     if (!strcmp(argv[i], "-b")) {
       dump_backtrace = true;
     } else if (!have_tid) {
       tid = atoi(argv[i]);
       have_tid = true;
     } else {
       usage();
       return 1;
     }
   }
   if (!have_tid) {
     usage();
     return 1;
   }
   return do_explicit_dump(tid, dump_backtrace);
 }
	/*
	* Copyright 2006, The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include <stdio.h>
	#include <errno.h>
	#include <signal.h>
	#include <pthread.h>
	#include <stdarg.h>
	#include <fcntl.h>
	#include <sys/types.h>
	#include <dirent.h>
	#include <time.h>

	#include <sys/ptrace.h>
	#include <sys/wait.h>
	#include <elf.h>
	#include <sys/stat.h>
	#include <sys/poll.h>

	#include <selinux/android.h>

	#include <log/logger.h>

	#include <cutils/sockets.h>
	#include <cutils/properties.h>
	#include <cutils/debugger.h>

	#include <linux/input.h>

	#include <private/android_filesystem_config.h>

	#include "backtrace.h"
	#include "getevent.h"
	#include "tombstone.h"
	#include "utility.h"

	struct debugger_request_t {
	debugger_action_t action;
	pid_t pid, tid;
	uid_t uid, gid;
	uintptr_t abort_msg_address;
	int32_t original_si_code;
	};

	static void wait_for_user_action(const debugger_request_t &request) {
	// Find out the name of the process that crashed.
	char path[64];
	snprintf(path, sizeof(path), "/proc/%d/exe", request.pid);

	char exe[PATH_MAX];
	int count;
	if ((count = readlink(path, exe, sizeof(exe) - 1)) == -1) {
	ALOGE("readlink('%s') failed: %s", path, strerror(errno));
	strlcpy(exe, "unknown", sizeof(exe));
	} else {
	exe[count] = '\0';
	}

	// Explain how to attach the debugger.
	ALOGI("********************************************************\n"
	"* Process %d has been suspended while crashing.\n"
	"* To attach gdbserver for a gdb connection on port 5039\n"
	"* and start gdbclient:\n"
	"*\n"
	"* gdbclient %s :5039 %d\n"
	"*\n"
	"* Wait for gdb to start, then press the VOLUME DOWN key\n"
	"* to let the process continue crashing.\n"
	"********************************************************",
	request.pid, exe, request.tid);

	// Wait for VOLUME DOWN.
	if (init_getevent() == 0) {
	while (true) {
	input_event e;
	if (get_event(&e, -1) == 0) {
	if (e.type == EV_KEY && e.code == KEY_VOLUMEDOWN && e.value == 0) {
	break;
	}
	}
	}
	uninit_getevent();
	}

	ALOGI("debuggerd resuming process %d", request.pid);
	}

	static int get_process_info(pid_t tid, pid_t* out_pid, uid_t* out_uid, uid_t* out_gid) {
	char path[64];
	snprintf(path, sizeof(path), "/proc/%d/status", tid);

	FILE* fp = fopen(path, "r");
	if (!fp) {
	return -1;
	}

	int fields = 0;
	char line[1024];
	while (fgets(line, sizeof(line), fp)) {
	size_t len = strlen(line);
	if (len > 6 && !memcmp(line, "Tgid:\t", 6)) {
	*out_pid = atoi(line + 6);
	fields \|= 1;
	} else if (len > 5 && !memcmp(line, "Uid:\t", 5)) {
	*out_uid = atoi(line + 5);
	fields \|= 2;
	} else if (len > 5 && !memcmp(line, "Gid:\t", 5)) {
	*out_gid = atoi(line + 5);
	fields \|= 4;
	}
	}
	fclose(fp);
	return fields == 7 ? 0 : -1;
	}

	static int selinux_enabled;

	/*
	* Corresponds with debugger_action_t enum type in
	* include/cutils/debugger.h.
	*/
	static const char *debuggerd_perms[] = {
	NULL, /* crash is only used on self, no check applied */
	"dump_tombstone",
	"dump_backtrace"
	};

	static bool selinux_action_allowed(int s, pid_t tid, debugger_action_t action)
	{
	char scon = NULL, tcon = NULL;
	const char *tclass = "debuggerd";
	const char *perm;
	bool allowed = false;

	if (selinux_enabled <= 0)
	return true;

	if (action <= 0 \|\| action >= (sizeof(debuggerd_perms)/sizeof(debuggerd_perms[0]))) {
	ALOGE("SELinux: No permission defined for debugger action %d", action);
	return false;
	}

	perm = debuggerd_perms[action];

	if (getpeercon(s, &scon) < 0) {
	ALOGE("Cannot get peer context from socket\n");
	goto out;
	}

	if (getpidcon(tid, &tcon) < 0) {
	ALOGE("Cannot get context for tid %d\n", tid);
	goto out;
	}

	allowed = (selinux_check_access(scon, tcon, tclass, perm, NULL) == 0);

	out:
	freecon(scon);
	freecon(tcon);
	return allowed;
	}

	static int read_request(int fd, debugger_request_t* out_request) {
	ucred cr;
	socklen_t len = sizeof(cr);
	int status = getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
	if (status != 0) {
	ALOGE("cannot get credentials");
	return -1;
	}

	ALOGV("reading tid");
	fcntl(fd, F_SETFL, O_NONBLOCK);

	pollfd pollfds[1];
	pollfds[0].fd = fd;
	pollfds[0].events = POLLIN;
	pollfds[0].revents = 0;
	status = TEMP_FAILURE_RETRY(poll(pollfds, 1, 3000));
	if (status != 1) {
	ALOGE("timed out reading tid (from pid=%d uid=%d)\n", cr.pid, cr.uid);
	return -1;
	}

	debugger_msg_t msg;
	memset(&msg, 0, sizeof(msg));
	status = TEMP_FAILURE_RETRY(read(fd, &msg, sizeof(msg)));
	if (status < 0) {
	ALOGE("read failure? %s (pid=%d uid=%d)\n", strerror(errno), cr.pid, cr.uid);
	return -1;
	}
	if (status != sizeof(debugger_msg_t)) {
	ALOGE("invalid crash request of size %d (from pid=%d uid=%d)\n", status, cr.pid, cr.uid);
	return -1;
	}

	out_request->action = msg.action;
	out_request->tid = msg.tid;
	out_request->pid = cr.pid;
	out_request->uid = cr.uid;
	out_request->gid = cr.gid;
	out_request->abort_msg_address = msg.abort_msg_address;
	out_request->original_si_code = msg.original_si_code;

	if (msg.action == DEBUGGER_ACTION_CRASH) {
	// Ensure that the tid reported by the crashing process is valid.
	char buf[64];
	struct stat s;
	snprintf(buf, sizeof buf, "/proc/%d/task/%d", out_request->pid, out_request->tid);
	if (stat(buf, &s)) {
	ALOGE("tid %d does not exist in pid %d. ignoring debug request\n",
	out_request->tid, out_request->pid);
	return -1;
	}
	} else if (cr.uid == 0
	\|\| (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
	// Only root or system can ask us to attach to any process and dump it explicitly.
	// However, system is only allowed to collect backtraces but cannot dump tombstones.
	status = get_process_info(out_request->tid, &out_request->pid,
	&out_request->uid, &out_request->gid);
	if (status < 0) {
	ALOGE("tid %d does not exist. ignoring explicit dump request\n", out_request->tid);
	return -1;
	}

	if (!selinux_action_allowed(fd, out_request->tid, out_request->action))
	return -1;
	} else {
	// No one else is allowed to dump arbitrary processes.
	return -1;
	}
	return 0;
	}

	static bool should_attach_gdb(debugger_request_t* request) {
	if (request->action == DEBUGGER_ACTION_CRASH) {
	char value[PROPERTY_VALUE_MAX];
	property_get("debug.db.uid", value, "-1");
	int debug_uid = atoi(value);
	return debug_uid >= 0 && request->uid <= (uid_t)debug_uid;
	}
	return false;
	}

	static void handle_request(int fd) {
	ALOGV("handle_request(%d)\n", fd);

	debugger_request_t request;
	memset(&request, 0, sizeof(request));
	int status = read_request(fd, &request);
	if (!status) {
	ALOGV("BOOM: pid=%d uid=%d gid=%d tid=%d\n",
	request.pid, request.uid, request.gid, request.tid);

	// At this point, the thread that made the request is blocked in
	// a read() call. If the thread has crashed, then this gives us
	// time to PTRACE_ATTACH to it before it has a chance to really fault.
	//
	// The PTRACE_ATTACH sends a SIGSTOP to the target process, but it
	// won't necessarily have stopped by the time ptrace() returns. (We
	// currently assume it does.) We write to the file descriptor to
	// ensure that it can run as soon as we call PTRACE_CONT below.
	// See details in bionic/libc/linker/debugger.c, in function
	// debugger_signal_handler().
	if (ptrace(PTRACE_ATTACH, request.tid, 0, 0)) {
	ALOGE("ptrace attach failed: %s\n", strerror(errno));
	} else {
	bool detach_failed = false;
	bool tid_unresponsive = false;
	bool attach_gdb = should_attach_gdb(&request);
	if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
	ALOGE("failed responding to client: %s\n", strerror(errno));
	} else {
	char* tombstone_path = NULL;

	if (request.action == DEBUGGER_ACTION_CRASH) {
	close(fd);
	fd = -1;
	}

	int total_sleep_time_usec = 0;
	for (;;) {
	int signal = wait_for_sigstop(request.tid, &total_sleep_time_usec, &detach_failed);
	if (signal == -1) {
	tid_unresponsive = true;
	break;
	}

	switch (signal) {
	case SIGSTOP:
	if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
	ALOGV("stopped -- dumping to tombstone\n");
	tombstone_path = engrave_tombstone(request.pid, request.tid,
	signal, request.original_si_code,
	request.abort_msg_address, true,
	&detach_failed, &total_sleep_time_usec);
	} else if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE) {
	ALOGV("stopped -- dumping to fd\n");
	dump_backtrace(fd, -1, request.pid, request.tid, &detach_failed,
	&total_sleep_time_usec);
	} else {
	ALOGV("stopped -- continuing\n");
	status = ptrace(PTRACE_CONT, request.tid, 0, 0);
	if (status) {
	ALOGE("ptrace continue failed: %s\n", strerror(errno));
	}
	continue; // loop again
	}
	break;

	case SIGABRT:
	case SIGBUS:
	case SIGFPE:
	case SIGILL:
	case SIGPIPE:
	case SIGSEGV:
	#ifdef SIGSTKFLT
	case SIGSTKFLT:
	#endif
	case SIGTRAP:
	ALOGV("stopped -- fatal signal\n");
	// Send a SIGSTOP to the process to make all of
	// the non-signaled threads stop moving. Without
	// this we get a lot of "ptrace detach failed:
	// No such process".
	kill(request.pid, SIGSTOP);
	// don't dump sibling threads when attaching to GDB because it
	// makes the process less reliable, apparently...
	tombstone_path = engrave_tombstone(request.pid, request.tid,
	signal, request.original_si_code,
	request.abort_msg_address, !attach_gdb,
	&detach_failed, &total_sleep_time_usec);
	break;

	default:
	ALOGE("process stopped due to unexpected signal %d\n", signal);
	break;
	}
	break;
	}

	if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
	if (tombstone_path) {
	write(fd, tombstone_path, strlen(tombstone_path));
	}
	close(fd);
	fd = -1;
	}
	free(tombstone_path);
	}

	if (!tid_unresponsive) {
	ALOGV("detaching");
	if (attach_gdb) {
	// stop the process so we can debug
	kill(request.pid, SIGSTOP);
	}
	if (ptrace(PTRACE_DETACH, request.tid, 0, 0)) {
	ALOGE("ptrace detach from %d failed: %s", request.tid, strerror(errno));
	detach_failed = true;
	} else if (attach_gdb) {
	// if debug.db.uid is set, its value indicates if we should wait
	// for user action for the crashing process.
	// in this case, we log a message and turn the debug LED on
	// waiting for a gdb connection (for instance)
	wait_for_user_action(request);
	}
	}

	// resume stopped process (so it can crash in peace).
	kill(request.pid, SIGCONT);

	// If we didn't successfully detach, we're still the parent, and the
	// actual parent won't receive a death notification via wait(2). At this point
	// there's not much we can do about that.
	if (detach_failed) {
	ALOGE("debuggerd committing suicide to free the zombie!\n");
	kill(getpid(), SIGKILL);
	}
	}

	}
	if (fd >= 0) {
	close(fd);
	}
	}

	static int do_server() {
	// debuggerd crashes can't be reported to debuggerd.
	// Reset all of the crash handlers.
	signal(SIGABRT, SIG_DFL);
	signal(SIGBUS, SIG_DFL);
	signal(SIGFPE, SIG_DFL);
	signal(SIGILL, SIG_DFL);
	signal(SIGSEGV, SIG_DFL);
	#ifdef SIGSTKFLT
	signal(SIGSTKFLT, SIG_DFL);
	#endif
	signal(SIGTRAP, SIG_DFL);

	// Ignore failed writes to closed sockets
	signal(SIGPIPE, SIG_IGN);

	int logsocket = socket_local_client("logd", ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_DGRAM);
	if (logsocket < 0) {
	logsocket = -1;
	} else {
	fcntl(logsocket, F_SETFD, FD_CLOEXEC);
	}

	struct sigaction act;
	act.sa_handler = SIG_DFL;
	sigemptyset(&act.sa_mask);
	sigaddset(&act.sa_mask,SIGCHLD);
	act.sa_flags = SA_NOCLDWAIT;
	sigaction(SIGCHLD, &act, 0);

	int s = socket_local_server(DEBUGGER_SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_STREAM);
	if (s < 0)
	return 1;
	fcntl(s, F_SETFD, FD_CLOEXEC);

	ALOGI("debuggerd: " __DATE__ " " __TIME__ "\n");

	for (;;) {
	sockaddr addr;
	socklen_t alen = sizeof(addr);

	ALOGV("waiting for connection\n");
	int fd = accept(s, &addr, &alen);
	if (fd < 0) {
	ALOGV("accept failed: %s\n", strerror(errno));
	continue;
	}

	fcntl(fd, F_SETFD, FD_CLOEXEC);

	handle_request(fd);
	}
	return 0;
	}

	static int do_explicit_dump(pid_t tid, bool dump_backtrace) {
	fprintf(stdout, "Sending request to dump task %d.\n", tid);

	if (dump_backtrace) {
	fflush(stdout);
	if (dump_backtrace_to_file(tid, fileno(stdout)) < 0) {
	fputs("Error dumping backtrace.\n", stderr);
	return 1;
	}
	} else {
	char tombstone_path[PATH_MAX];
	if (dump_tombstone(tid, tombstone_path, sizeof(tombstone_path)) < 0) {
	fputs("Error dumping tombstone.\n", stderr);
	return 1;
	}
	fprintf(stderr, "Tombstone written to: %s\n", tombstone_path);
	}
	return 0;
	}

	static void usage() {
	fputs("Usage: -b [<tid>]\n"
	" -b dump backtrace to console, otherwise dump full tombstone file\n"
	"\n"
	"If tid specified, sends a request to debuggerd to dump that task.\n"
	"Otherwise, starts the debuggerd server.\n", stderr);
	}

	int main(int argc, char** argv) {
	union selinux_callback cb;
	if (argc == 1) {
	selinux_enabled = is_selinux_enabled();
	cb.func_log = selinux_log_callback;
	selinux_set_callback(SELINUX_CB_LOG, cb);
	return do_server();
	}

	bool dump_backtrace = false;
	bool have_tid = false;
	pid_t tid = 0;
	for (int i = 1; i < argc; i++) {
	if (!strcmp(argv[i], "-b")) {
	dump_backtrace = true;
	} else if (!have_tid) {
	tid = atoi(argv[i]);
	have_tid = true;
	} else {
	usage();
	return 1;
	}
	}
	if (!have_tid) {
	usage();
	return 1;
	}
	return do_explicit_dump(tid, dump_backtrace);
	}