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 <log/logd.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"

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

 static int write_string(const char* file, const char* string) {
   int len;
   int fd;
   ssize_t amt;
   fd = open(file, O_RDWR);
   len = strlen(string);
   if (fd < 0)
     return -errno;
   amt = write(fd, string, len);
   close(fd);
   return amt >= 0 ? 0 : -errno;
 }

 static void init_debug_led() {
   // trout leds
   write_string("/sys/class/leds/red/brightness", "0");
   write_string("/sys/class/leds/green/brightness", "0");
   write_string("/sys/class/leds/blue/brightness", "0");
   write_string("/sys/class/leds/red/device/blink", "0");
   // sardine leds
   write_string("/sys/class/leds/left/cadence", "0,0");
 }

 static void enable_debug_led() {
   // trout leds
   write_string("/sys/class/leds/red/brightness", "255");
   // sardine leds
   write_string("/sys/class/leds/left/cadence", "1,0");
 }

 static void disable_debug_led() {
   // trout leds
   write_string("/sys/class/leds/red/brightness", "0");
   // sardine leds
   write_string("/sys/class/leds/left/cadence", "0,0");
 }

 static void wait_for_user_action(pid_t pid) {
   // First log a helpful message
   LOG(    "********************************************************\n"
           "* Process %d has been suspended while crashing.  To\n"
           "* attach gdbserver for a gdb connection on port 5039\n"
           "* and start gdbclient:\n"
           "*\n"
           "*     gdbclient app_process :5039 %d\n"
           "*\n"
           "* Wait for gdb to start, then press HOME or VOLUME DOWN key\n"
           "* to let the process continue crashing.\n"
           "********************************************************\n",
           pid, pid);

   // wait for HOME or VOLUME DOWN key
   if (init_getevent() == 0) {
     int ms = 1200 / 10;
     int dit = 1;
     int dah = 3*dit;
     int _       = -dit;
     int ___     = 3*_;
     int _______ = 7*_;
     const int codes[] = {
       dit,_,dit,_,dit,___,dah,_,dah,_,dah,___,dit,_,dit,_,dit,_______
     };
     size_t s = 0;
     struct input_event e;
     bool done = false;
     init_debug_led();
     enable_debug_led();
     do {
       int timeout = abs(codes[s]) * ms;
       int res = get_event(&e, timeout);
       if (res == 0) {
         if (e.type == EV_KEY
             && (e.code == KEY_HOME || e.code == KEY_VOLUMEDOWN)
             && e.value == 0) {
           done = true;
         }
       } else if (res == 1) {
         if (++s >= sizeof(codes)/sizeof(*codes))
           s = 0;
         if (codes[s] > 0) {
           enable_debug_led();
         } else {
           disable_debug_led();
         }
       }
     } while (!done);
     uninit_getevent();
   }

   // don't forget to turn debug led off
   disable_debug_led();
   LOG("debuggerd resuming process %d", 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 read_request(int fd, debugger_request_t* out_request) {
   struct ucred cr;
   int len = sizeof(cr);
   int status = getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
   if (status != 0) {
     LOG("cannot get credentials\n");
     return -1;
   }

   XLOG("reading tid\n");
   fcntl(fd, F_SETFL, O_NONBLOCK);

   struct 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) {
     LOG("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) {
     LOG("read failure? %s (pid=%d uid=%d)\n", strerror(errno), cr.pid, cr.uid);
     return -1;
   }
   if (status == sizeof(debugger_msg_t)) {
     XLOG("crash request of size %d abort_msg_address=0x%" PRIPTR "\n",
          status, msg.abort_msg_address);
   } else {
     LOG("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;

   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)) {
       LOG("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) {
       LOG("tid %d does not exist. ignoring explicit dump request\n", out_request->tid);
       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) {
   XLOG("handle_request(%d)\n", fd);

   debugger_request_t request;
   memset(&request, 0, sizeof(request));
   int status = read_request(fd, &request);
   if (!status) {
     XLOG("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)) {
       LOG("ptrace attach failed: %s\n", strerror(errno));
     } else {
       bool detach_failed = false;
       bool attach_gdb = should_attach_gdb(&request);
       if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
         LOG("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_signal(request.tid, &total_sleep_time_usec);
           if (signal < 0) {
             break;
           }

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

             case SIGILL:
             case SIGABRT:
             case SIGBUS:
             case SIGFPE:
             case SIGSEGV:
             case SIGPIPE:
 #ifdef SIGSTKFLT
             case SIGSTKFLT:
 #endif
               XLOG("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.abort_msg_address, !attach_gdb,
                   false, &detach_failed, &total_sleep_time_usec);
               break;

             default:
               XLOG("stopped -- unexpected signal\n");
               LOG("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);
       }

       XLOG("detaching\n");
       if (attach_gdb) {
         // stop the process so we can debug
         kill(request.pid, SIGSTOP);

         // detach so we can attach gdbserver
         if (ptrace(PTRACE_DETACH, request.tid, 0, 0)) {
           LOG("ptrace detach from %d failed: %s\n", request.tid, strerror(errno));
           detach_failed = true;
         }

         // 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.pid);
       } else {
         // just detach
         if (ptrace(PTRACE_DETACH, request.tid, 0, 0)) {
           LOG("ptrace detach from %d failed: %s\n", request.tid, strerror(errno));
           detach_failed = true;
         }
       }

       // 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) {
         LOG("debuggerd committing suicide to free the zombie!\n");
         kill(getpid(), SIGKILL);
       }
     }

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

 static int do_server() {
   int s;
   struct sigaction act;
   int logsocket = -1;

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

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

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

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

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

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

   for (;;) {
     struct sockaddr addr;
     socklen_t alen;
     int fd;

     alen = sizeof(addr);
     XLOG("waiting for connection\n");
     fd = accept(s, &addr, &alen);
     if (fd < 0) {
       XLOG("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) {
   if (argc == 1) {
     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 <log/logd.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"

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

	static int write_string(const char* file, const char* string) {
	int len;
	int fd;
	ssize_t amt;
	fd = open(file, O_RDWR);
	len = strlen(string);
	if (fd < 0)
	return -errno;
	amt = write(fd, string, len);
	close(fd);
	return amt >= 0 ? 0 : -errno;
	}

	static void init_debug_led() {
	// trout leds
	write_string("/sys/class/leds/red/brightness", "0");
	write_string("/sys/class/leds/green/brightness", "0");
	write_string("/sys/class/leds/blue/brightness", "0");
	write_string("/sys/class/leds/red/device/blink", "0");
	// sardine leds
	write_string("/sys/class/leds/left/cadence", "0,0");
	}

	static void enable_debug_led() {
	// trout leds
	write_string("/sys/class/leds/red/brightness", "255");
	// sardine leds
	write_string("/sys/class/leds/left/cadence", "1,0");
	}

	static void disable_debug_led() {
	// trout leds
	write_string("/sys/class/leds/red/brightness", "0");
	// sardine leds
	write_string("/sys/class/leds/left/cadence", "0,0");
	}

	static void wait_for_user_action(pid_t pid) {
	// First log a helpful message
	LOG( "********************************************************\n"
	"* Process %d has been suspended while crashing. To\n"
	"* attach gdbserver for a gdb connection on port 5039\n"
	"* and start gdbclient:\n"
	"*\n"
	"* gdbclient app_process :5039 %d\n"
	"*\n"
	"* Wait for gdb to start, then press HOME or VOLUME DOWN key\n"
	"* to let the process continue crashing.\n"
	"********************************************************\n",
	pid, pid);

	// wait for HOME or VOLUME DOWN key
	if (init_getevent() == 0) {
	int ms = 1200 / 10;
	int dit = 1;
	int dah = 3*dit;
	int _ = -dit;
	int ___ = 3*_;
	int _______ = 7*_;
	const int codes[] = {
	dit,_,dit,_,dit,___,dah,_,dah,_,dah,___,dit,_,dit,_,dit,_______
	};
	size_t s = 0;
	struct input_event e;
	bool done = false;
	init_debug_led();
	enable_debug_led();
	do {
	int timeout = abs(codes[s]) * ms;
	int res = get_event(&e, timeout);
	if (res == 0) {
	if (e.type == EV_KEY
	&& (e.code == KEY_HOME \|\| e.code == KEY_VOLUMEDOWN)
	&& e.value == 0) {
	done = true;
	}
	} else if (res == 1) {
	if (++s >= sizeof(codes)/sizeof(*codes))
	s = 0;
	if (codes[s] > 0) {
	enable_debug_led();
	} else {
	disable_debug_led();
	}
	}
	} while (!done);
	uninit_getevent();
	}

	// don't forget to turn debug led off
	disable_debug_led();
	LOG("debuggerd resuming process %d", 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 read_request(int fd, debugger_request_t* out_request) {
	struct ucred cr;
	int len = sizeof(cr);
	int status = getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
	if (status != 0) {
	LOG("cannot get credentials\n");
	return -1;
	}

	XLOG("reading tid\n");
	fcntl(fd, F_SETFL, O_NONBLOCK);

	struct 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) {
	LOG("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) {
	LOG("read failure? %s (pid=%d uid=%d)\n", strerror(errno), cr.pid, cr.uid);
	return -1;
	}
	if (status == sizeof(debugger_msg_t)) {
	XLOG("crash request of size %d abort_msg_address=0x%" PRIPTR "\n",
	status, msg.abort_msg_address);
	} else {
	LOG("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;

	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)) {
	LOG("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) {
	LOG("tid %d does not exist. ignoring explicit dump request\n", out_request->tid);
	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) {
	XLOG("handle_request(%d)\n", fd);

	debugger_request_t request;
	memset(&request, 0, sizeof(request));
	int status = read_request(fd, &request);
	if (!status) {
	XLOG("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)) {
	LOG("ptrace attach failed: %s\n", strerror(errno));
	} else {
	bool detach_failed = false;
	bool attach_gdb = should_attach_gdb(&request);
	if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
	LOG("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_signal(request.tid, &total_sleep_time_usec);
	if (signal < 0) {
	break;
	}

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

	case SIGILL:
	case SIGABRT:
	case SIGBUS:
	case SIGFPE:
	case SIGSEGV:
	case SIGPIPE:
	#ifdef SIGSTKFLT
	case SIGSTKFLT:
	#endif
	XLOG("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.abort_msg_address, !attach_gdb,
	false, &detach_failed, &total_sleep_time_usec);
	break;

	default:
	XLOG("stopped -- unexpected signal\n");
	LOG("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);
	}

	XLOG("detaching\n");
	if (attach_gdb) {
	// stop the process so we can debug
	kill(request.pid, SIGSTOP);

	// detach so we can attach gdbserver
	if (ptrace(PTRACE_DETACH, request.tid, 0, 0)) {
	LOG("ptrace detach from %d failed: %s\n", request.tid, strerror(errno));
	detach_failed = true;
	}

	// 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.pid);
	} else {
	// just detach
	if (ptrace(PTRACE_DETACH, request.tid, 0, 0)) {
	LOG("ptrace detach from %d failed: %s\n", request.tid, strerror(errno));
	detach_failed = true;
	}
	}

	// 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) {
	LOG("debuggerd committing suicide to free the zombie!\n");
	kill(getpid(), SIGKILL);
	}
	}

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

	static int do_server() {
	int s;
	struct sigaction act;
	int logsocket = -1;

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

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

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

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

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

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

	for (;;) {
	struct sockaddr addr;
	socklen_t alen;
	int fd;

	alen = sizeof(addr);
	XLOG("waiting for connection\n");
	fd = accept(s, &addr, &alen);
	if (fd < 0) {
	XLOG("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) {
	if (argc == 1) {
	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);
	}