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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "base/debug/debugger.h"
      6 #include "build/build_config.h"
      7 
      8 #include <errno.h>
      9 #include <fcntl.h>
     10 #include <stdio.h>
     11 #include <stdlib.h>
     12 #include <sys/param.h>
     13 #include <sys/stat.h>
     14 #include <sys/types.h>
     15 #include <unistd.h>
     16 
     17 #include <string>
     18 #include <vector>
     19 
     20 #if defined(__GLIBCXX__)
     21 #include <cxxabi.h>
     22 #endif
     23 
     24 #if defined(OS_MACOSX)
     25 #include <AvailabilityMacros.h>
     26 #endif
     27 
     28 #if defined(OS_MACOSX) || defined(OS_BSD)
     29 #include <sys/sysctl.h>
     30 #endif
     31 
     32 #if defined(OS_FREEBSD)
     33 #include <sys/user.h>
     34 #endif
     35 
     36 #include <ostream>
     37 
     38 #include "base/basictypes.h"
     39 #include "base/logging.h"
     40 #include "base/memory/scoped_ptr.h"
     41 #include "base/posix/eintr_wrapper.h"
     42 #include "base/safe_strerror_posix.h"
     43 #include "base/strings/string_piece.h"
     44 #include "base/strings/stringprintf.h"
     45 
     46 #if defined(USE_SYMBOLIZE)
     47 #include "base/third_party/symbolize/symbolize.h"
     48 #endif
     49 
     50 #if defined(OS_ANDROID)
     51 #include "base/threading/platform_thread.h"
     52 #endif
     53 
     54 namespace base {
     55 namespace debug {
     56 
     57 bool SpawnDebuggerOnProcess(unsigned process_id) {
     58 #if OS_ANDROID || OS_NACL
     59   NOTIMPLEMENTED();
     60   return false;
     61 #else
     62   const std::string debug_cmd =
     63       StringPrintf("xterm -e 'gdb --pid=%u' &", process_id);
     64   LOG(WARNING) << "Starting debugger on pid " << process_id
     65                << " with command `" << debug_cmd << "`";
     66   int ret = system(debug_cmd.c_str());
     67   if (ret == -1)
     68     return false;
     69   return true;
     70 #endif
     71 }
     72 
     73 #if defined(OS_MACOSX) || defined(OS_BSD)
     74 
     75 // Based on Apple's recommended method as described in
     76 // http://developer.apple.com/qa/qa2004/qa1361.html
     77 bool BeingDebugged() {
     78   // NOTE: This code MUST be async-signal safe (it's used by in-process
     79   // stack dumping signal handler). NO malloc or stdio is allowed here.
     80   //
     81   // While some code used below may be async-signal unsafe, note how
     82   // the result is cached (see |is_set| and |being_debugged| static variables
     83   // right below). If this code is properly warmed-up early
     84   // in the start-up process, it should be safe to use later.
     85 
     86   // If the process is sandboxed then we can't use the sysctl, so cache the
     87   // value.
     88   static bool is_set = false;
     89   static bool being_debugged = false;
     90 
     91   if (is_set)
     92     return being_debugged;
     93 
     94   // Initialize mib, which tells sysctl what info we want.  In this case,
     95   // we're looking for information about a specific process ID.
     96   int mib[] = {
     97     CTL_KERN,
     98     KERN_PROC,
     99     KERN_PROC_PID,
    100     getpid()
    101 #if defined(OS_OPENBSD)
    102     , sizeof(struct kinfo_proc),
    103     0
    104 #endif
    105   };
    106 
    107   // Caution: struct kinfo_proc is marked __APPLE_API_UNSTABLE.  The source and
    108   // binary interfaces may change.
    109   struct kinfo_proc info;
    110   size_t info_size = sizeof(info);
    111 
    112 #if defined(OS_OPENBSD)
    113   if (sysctl(mib, arraysize(mib), NULL, &info_size, NULL, 0) < 0)
    114     return -1;
    115 
    116   mib[5] = (info_size / sizeof(struct kinfo_proc));
    117 #endif
    118 
    119   int sysctl_result = sysctl(mib, arraysize(mib), &info, &info_size, NULL, 0);
    120   DCHECK_EQ(sysctl_result, 0);
    121   if (sysctl_result != 0) {
    122     is_set = true;
    123     being_debugged = false;
    124     return being_debugged;
    125   }
    126 
    127   // This process is being debugged if the P_TRACED flag is set.
    128   is_set = true;
    129 #if defined(OS_FREEBSD)
    130   being_debugged = (info.ki_flag & P_TRACED) != 0;
    131 #elif defined(OS_BSD)
    132   being_debugged = (info.p_flag & P_TRACED) != 0;
    133 #else
    134   being_debugged = (info.kp_proc.p_flag & P_TRACED) != 0;
    135 #endif
    136   return being_debugged;
    137 }
    138 
    139 #elif defined(OS_LINUX) || defined(OS_ANDROID)
    140 
    141 // We can look in /proc/self/status for TracerPid.  We are likely used in crash
    142 // handling, so we are careful not to use the heap or have side effects.
    143 // Another option that is common is to try to ptrace yourself, but then we
    144 // can't detach without forking(), and that's not so great.
    145 // static
    146 bool BeingDebugged() {
    147   // NOTE: This code MUST be async-signal safe (it's used by in-process
    148   // stack dumping signal handler). NO malloc or stdio is allowed here.
    149 
    150   int status_fd = open("/proc/self/status", O_RDONLY);
    151   if (status_fd == -1)
    152     return false;
    153 
    154   // We assume our line will be in the first 1024 characters and that we can
    155   // read this much all at once.  In practice this will generally be true.
    156   // This simplifies and speeds up things considerably.
    157   char buf[1024];
    158 
    159   ssize_t num_read = HANDLE_EINTR(read(status_fd, buf, sizeof(buf)));
    160   if (IGNORE_EINTR(close(status_fd)) < 0)
    161     return false;
    162 
    163   if (num_read <= 0)
    164     return false;
    165 
    166   StringPiece status(buf, num_read);
    167   StringPiece tracer("TracerPid:\t");
    168 
    169   StringPiece::size_type pid_index = status.find(tracer);
    170   if (pid_index == StringPiece::npos)
    171     return false;
    172 
    173   // Our pid is 0 without a debugger, assume this for any pid starting with 0.
    174   pid_index += tracer.size();
    175   return pid_index < status.size() && status[pid_index] != '0';
    176 }
    177 
    178 #else
    179 
    180 bool BeingDebugged() {
    181   NOTIMPLEMENTED();
    182   return false;
    183 }
    184 
    185 #endif
    186 
    187 // We want to break into the debugger in Debug mode, and cause a crash dump in
    188 // Release mode. Breakpad behaves as follows:
    189 //
    190 // +-------+-----------------+-----------------+
    191 // | OS    | Dump on SIGTRAP | Dump on SIGABRT |
    192 // +-------+-----------------+-----------------+
    193 // | Linux |       N         |        Y        |
    194 // | Mac   |       Y         |        N        |
    195 // +-------+-----------------+-----------------+
    196 //
    197 // Thus we do the following:
    198 // Linux: Debug mode if a debugger is attached, send SIGTRAP; otherwise send
    199 //        SIGABRT
    200 // Mac: Always send SIGTRAP.
    201 
    202 #if defined(ARCH_CPU_ARM_FAMILY)
    203 #define DEBUG_BREAK_ASM() asm("bkpt 0")
    204 #elif defined(ARCH_CPU_MIPS_FAMILY)
    205 #define DEBUG_BREAK_ASM() asm("break 2")
    206 #elif defined(ARCH_CPU_X86_FAMILY)
    207 #define DEBUG_BREAK_ASM() asm("int3")
    208 #endif
    209 
    210 #if defined(NDEBUG) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
    211 #define DEBUG_BREAK() abort()
    212 #elif defined(OS_NACL)
    213 // The NaCl verifier doesn't let use use int3.  For now, we call abort().  We
    214 // should ask for advice from some NaCl experts about the optimum thing here.
    215 // http://code.google.com/p/nativeclient/issues/detail?id=645
    216 #define DEBUG_BREAK() abort()
    217 #elif !defined(OS_MACOSX)
    218 // Though Android has a "helpful" process called debuggerd to catch native
    219 // signals on the general assumption that they are fatal errors. If no debugger
    220 // is attached, we call abort since Breakpad needs SIGABRT to create a dump.
    221 // When debugger is attached, for ARM platform the bkpt instruction appears
    222 // to cause SIGBUS which is trapped by debuggerd, and we've had great
    223 // difficulty continuing in a debugger once we stop from SIG triggered by native
    224 // code, use GDB to set |go| to 1 to resume execution; for X86 platform, use
    225 // "int3" to setup breakpiont and raise SIGTRAP.
    226 //
    227 // On other POSIX architectures, except Mac OS X, we use the same logic to
    228 // ensure that breakpad creates a dump on crashes while it is still possible to
    229 // use a debugger.
    230 namespace {
    231 void DebugBreak() {
    232   if (!BeingDebugged()) {
    233     abort();
    234   } else {
    235 #if defined(DEBUG_BREAK_ASM)
    236     DEBUG_BREAK_ASM();
    237 #else
    238     volatile int go = 0;
    239     while (!go) {
    240       base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(100));
    241     }
    242 #endif
    243   }
    244 }
    245 }  // namespace
    246 #define DEBUG_BREAK() DebugBreak()
    247 #elif defined(DEBUG_BREAK_ASM)
    248 #define DEBUG_BREAK() DEBUG_BREAK_ASM()
    249 #else
    250 #error "Don't know how to debug break on this architecture/OS"
    251 #endif
    252 
    253 void BreakDebugger() {
    254   // NOTE: This code MUST be async-signal safe (it's used by in-process
    255   // stack dumping signal handler). NO malloc or stdio is allowed here.
    256 
    257   DEBUG_BREAK();
    258 #if defined(OS_ANDROID) && !defined(OFFICIAL_BUILD)
    259   // For Android development we always build release (debug builds are
    260   // unmanageably large), so the unofficial build is used for debugging. It is
    261   // helpful to be able to insert BreakDebugger() statements in the source,
    262   // attach the debugger, inspect the state of the program and then resume it by
    263   // setting the 'go' variable above.
    264 #elif defined(NDEBUG)
    265   // Terminate the program after signaling the debug break.
    266   _exit(1);
    267 #endif
    268 }
    269 
    270 }  // namespace debug
    271 }  // namespace base
    272