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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 <vector>
     18 
     19 #if defined(__GLIBCXX__)
     20 #include <cxxabi.h>
     21 #endif
     22 
     23 #if defined(OS_MACOSX)
     24 #include <AvailabilityMacros.h>
     25 #endif
     26 
     27 #if defined(OS_MACOSX) || defined(OS_BSD)
     28 #include <sys/sysctl.h>
     29 #endif
     30 
     31 #if defined(OS_FREEBSD)
     32 #include <sys/user.h>
     33 #endif
     34 
     35 #include <ostream>
     36 
     37 #include "base/basictypes.h"
     38 #include "base/logging.h"
     39 #include "base/memory/scoped_ptr.h"
     40 #include "base/posix/eintr_wrapper.h"
     41 #include "base/safe_strerror_posix.h"
     42 #include "base/strings/string_piece.h"
     43 
     44 #if defined(USE_SYMBOLIZE)
     45 #include "base/third_party/symbolize/symbolize.h"
     46 #endif
     47 
     48 #if defined(OS_ANDROID)
     49 #include "base/threading/platform_thread.h"
     50 #endif
     51 
     52 namespace base {
     53 namespace debug {
     54 
     55 #if defined(OS_MACOSX) || defined(OS_BSD)
     56 
     57 // Based on Apple's recommended method as described in
     58 // http://developer.apple.com/qa/qa2004/qa1361.html
     59 bool BeingDebugged() {
     60   // NOTE: This code MUST be async-signal safe (it's used by in-process
     61   // stack dumping signal handler). NO malloc or stdio is allowed here.
     62   //
     63   // While some code used below may be async-signal unsafe, note how
     64   // the result is cached (see |is_set| and |being_debugged| static variables
     65   // right below). If this code is properly warmed-up early
     66   // in the start-up process, it should be safe to use later.
     67 
     68   // If the process is sandboxed then we can't use the sysctl, so cache the
     69   // value.
     70   static bool is_set = false;
     71   static bool being_debugged = false;
     72 
     73   if (is_set)
     74     return being_debugged;
     75 
     76   // Initialize mib, which tells sysctl what info we want.  In this case,
     77   // we're looking for information about a specific process ID.
     78   int mib[] = {
     79     CTL_KERN,
     80     KERN_PROC,
     81     KERN_PROC_PID,
     82     getpid()
     83 #if defined(OS_OPENBSD)
     84     , sizeof(struct kinfo_proc),
     85     0
     86 #endif
     87   };
     88 
     89   // Caution: struct kinfo_proc is marked __APPLE_API_UNSTABLE.  The source and
     90   // binary interfaces may change.
     91   struct kinfo_proc info;
     92   size_t info_size = sizeof(info);
     93 
     94 #if defined(OS_OPENBSD)
     95   if (sysctl(mib, arraysize(mib), NULL, &info_size, NULL, 0) < 0)
     96     return -1;
     97 
     98   mib[5] = (info_size / sizeof(struct kinfo_proc));
     99 #endif
    100 
    101   int sysctl_result = sysctl(mib, arraysize(mib), &info, &info_size, NULL, 0);
    102   DCHECK_EQ(sysctl_result, 0);
    103   if (sysctl_result != 0) {
    104     is_set = true;
    105     being_debugged = false;
    106     return being_debugged;
    107   }
    108 
    109   // This process is being debugged if the P_TRACED flag is set.
    110   is_set = true;
    111 #if defined(OS_FREEBSD)
    112   being_debugged = (info.ki_flag & P_TRACED) != 0;
    113 #elif defined(OS_BSD)
    114   being_debugged = (info.p_flag & P_TRACED) != 0;
    115 #else
    116   being_debugged = (info.kp_proc.p_flag & P_TRACED) != 0;
    117 #endif
    118   return being_debugged;
    119 }
    120 
    121 #elif defined(OS_LINUX) || defined(OS_ANDROID)
    122 
    123 // We can look in /proc/self/status for TracerPid.  We are likely used in crash
    124 // handling, so we are careful not to use the heap or have side effects.
    125 // Another option that is common is to try to ptrace yourself, but then we
    126 // can't detach without forking(), and that's not so great.
    127 // static
    128 bool BeingDebugged() {
    129   // NOTE: This code MUST be async-signal safe (it's used by in-process
    130   // stack dumping signal handler). NO malloc or stdio is allowed here.
    131 
    132   int status_fd = open("/proc/self/status", O_RDONLY);
    133   if (status_fd == -1)
    134     return false;
    135 
    136   // We assume our line will be in the first 1024 characters and that we can
    137   // read this much all at once.  In practice this will generally be true.
    138   // This simplifies and speeds up things considerably.
    139   char buf[1024];
    140 
    141   ssize_t num_read = HANDLE_EINTR(read(status_fd, buf, sizeof(buf)));
    142   if (IGNORE_EINTR(close(status_fd)) < 0)
    143     return false;
    144 
    145   if (num_read <= 0)
    146     return false;
    147 
    148   StringPiece status(buf, num_read);
    149   StringPiece tracer("TracerPid:\t");
    150 
    151   StringPiece::size_type pid_index = status.find(tracer);
    152   if (pid_index == StringPiece::npos)
    153     return false;
    154 
    155   // Our pid is 0 without a debugger, assume this for any pid starting with 0.
    156   pid_index += tracer.size();
    157   return pid_index < status.size() && status[pid_index] != '0';
    158 }
    159 
    160 #else
    161 
    162 bool BeingDebugged() {
    163   NOTIMPLEMENTED();
    164   return false;
    165 }
    166 
    167 #endif
    168 
    169 // We want to break into the debugger in Debug mode, and cause a crash dump in
    170 // Release mode. Breakpad behaves as follows:
    171 //
    172 // +-------+-----------------+-----------------+
    173 // | OS    | Dump on SIGTRAP | Dump on SIGABRT |
    174 // +-------+-----------------+-----------------+
    175 // | Linux |       N         |        Y        |
    176 // | Mac   |       Y         |        N        |
    177 // +-------+-----------------+-----------------+
    178 //
    179 // Thus we do the following:
    180 // Linux: Debug mode if a debugger is attached, send SIGTRAP; otherwise send
    181 //        SIGABRT
    182 // Mac: Always send SIGTRAP.
    183 
    184 #if defined(ARCH_CPU_ARMEL)
    185 #define DEBUG_BREAK_ASM() asm("bkpt 0")
    186 #elif defined(ARCH_CPU_ARM64)
    187 #define DEBUG_BREAK_ASM() asm("brk 0")
    188 #elif defined(ARCH_CPU_MIPS_FAMILY)
    189 #define DEBUG_BREAK_ASM() asm("break 2")
    190 #elif defined(ARCH_CPU_X86_FAMILY)
    191 #define DEBUG_BREAK_ASM() asm("int3")
    192 #endif
    193 
    194 #if defined(NDEBUG) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
    195 #define DEBUG_BREAK() abort()
    196 #elif defined(OS_NACL)
    197 // The NaCl verifier doesn't let use use int3.  For now, we call abort().  We
    198 // should ask for advice from some NaCl experts about the optimum thing here.
    199 // http://code.google.com/p/nativeclient/issues/detail?id=645
    200 #define DEBUG_BREAK() abort()
    201 #elif !defined(OS_MACOSX)
    202 // Though Android has a "helpful" process called debuggerd to catch native
    203 // signals on the general assumption that they are fatal errors. If no debugger
    204 // is attached, we call abort since Breakpad needs SIGABRT to create a dump.
    205 // When debugger is attached, for ARM platform the bkpt instruction appears
    206 // to cause SIGBUS which is trapped by debuggerd, and we've had great
    207 // difficulty continuing in a debugger once we stop from SIG triggered by native
    208 // code, use GDB to set |go| to 1 to resume execution; for X86 platform, use
    209 // "int3" to setup breakpiont and raise SIGTRAP.
    210 //
    211 // On other POSIX architectures, except Mac OS X, we use the same logic to
    212 // ensure that breakpad creates a dump on crashes while it is still possible to
    213 // use a debugger.
    214 namespace {
    215 void DebugBreak() {
    216   if (!BeingDebugged()) {
    217     abort();
    218   } else {
    219 #if defined(DEBUG_BREAK_ASM)
    220     DEBUG_BREAK_ASM();
    221 #else
    222     volatile int go = 0;
    223     while (!go) {
    224       base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(100));
    225     }
    226 #endif
    227   }
    228 }
    229 }  // namespace
    230 #define DEBUG_BREAK() DebugBreak()
    231 #elif defined(DEBUG_BREAK_ASM)
    232 #define DEBUG_BREAK() DEBUG_BREAK_ASM()
    233 #else
    234 #error "Don't know how to debug break on this architecture/OS"
    235 #endif
    236 
    237 void BreakDebugger() {
    238   // NOTE: This code MUST be async-signal safe (it's used by in-process
    239   // stack dumping signal handler). NO malloc or stdio is allowed here.
    240 
    241   DEBUG_BREAK();
    242 #if defined(OS_ANDROID) && !defined(OFFICIAL_BUILD)
    243   // For Android development we always build release (debug builds are
    244   // unmanageably large), so the unofficial build is used for debugging. It is
    245   // helpful to be able to insert BreakDebugger() statements in the source,
    246   // attach the debugger, inspect the state of the program and then resume it by
    247   // setting the 'go' variable above.
    248 #elif defined(NDEBUG)
    249   // Terminate the program after signaling the debug break.
    250   _exit(1);
    251 #endif
    252 }
    253 
    254 }  // namespace debug
    255 }  // namespace base
    256