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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 
      7 #include <errno.h>
      8 #include <fcntl.h>
      9 #include <stddef.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 <memory>
     18 #include <vector>
     19 
     20 #include "base/macros.h"
     21 #include "base/threading/platform_thread.h"
     22 #include "base/time/time.h"
     23 #include "build/build_config.h"
     24 
     25 #if defined(__GLIBCXX__)
     26 #include <cxxabi.h>
     27 #endif
     28 
     29 #if defined(OS_MACOSX)
     30 #include <AvailabilityMacros.h>
     31 #endif
     32 
     33 #if defined(OS_MACOSX) || defined(OS_BSD)
     34 #include <sys/sysctl.h>
     35 #endif
     36 
     37 #if defined(OS_FREEBSD)
     38 #include <sys/user.h>
     39 #endif
     40 
     41 #include <ostream>
     42 
     43 #include "base/debug/alias.h"
     44 #include "base/logging.h"
     45 #include "base/posix/eintr_wrapper.h"
     46 #include "base/strings/string_piece.h"
     47 
     48 #if defined(USE_SYMBOLIZE)
     49 #include "base/third_party/symbolize/symbolize.h"
     50 #endif
     51 
     52 #if defined(OS_ANDROID)
     53 #include "base/threading/platform_thread.h"
     54 #endif
     55 
     56 namespace base {
     57 namespace debug {
     58 
     59 #if defined(OS_MACOSX) || defined(OS_BSD)
     60 
     61 // Based on Apple's recommended method as described in
     62 // http://developer.apple.com/qa/qa2004/qa1361.html
     63 bool BeingDebugged() {
     64   // NOTE: This code MUST be async-signal safe (it's used by in-process
     65   // stack dumping signal handler). NO malloc or stdio is allowed here.
     66   //
     67   // While some code used below may be async-signal unsafe, note how
     68   // the result is cached (see |is_set| and |being_debugged| static variables
     69   // right below). If this code is properly warmed-up early
     70   // in the start-up process, it should be safe to use later.
     71 
     72   // If the process is sandboxed then we can't use the sysctl, so cache the
     73   // value.
     74   static bool is_set = false;
     75   static bool being_debugged = false;
     76 
     77   if (is_set)
     78     return being_debugged;
     79 
     80   // Initialize mib, which tells sysctl what info we want.  In this case,
     81   // we're looking for information about a specific process ID.
     82   int mib[] = {
     83     CTL_KERN,
     84     KERN_PROC,
     85     KERN_PROC_PID,
     86     getpid()
     87 #if defined(OS_OPENBSD)
     88     , sizeof(struct kinfo_proc),
     89     0
     90 #endif
     91   };
     92 
     93   // Caution: struct kinfo_proc is marked __APPLE_API_UNSTABLE.  The source and
     94   // binary interfaces may change.
     95   struct kinfo_proc info;
     96   size_t info_size = sizeof(info);
     97 
     98 #if defined(OS_OPENBSD)
     99   if (sysctl(mib, arraysize(mib), NULL, &info_size, NULL, 0) < 0)
    100     return -1;
    101 
    102   mib[5] = (info_size / sizeof(struct kinfo_proc));
    103 #endif
    104 
    105   int sysctl_result = sysctl(mib, arraysize(mib), &info, &info_size, NULL, 0);
    106   DCHECK_EQ(sysctl_result, 0);
    107   if (sysctl_result != 0) {
    108     is_set = true;
    109     being_debugged = false;
    110     return being_debugged;
    111   }
    112 
    113   // This process is being debugged if the P_TRACED flag is set.
    114   is_set = true;
    115 #if defined(OS_FREEBSD)
    116   being_debugged = (info.ki_flag & P_TRACED) != 0;
    117 #elif defined(OS_BSD)
    118   being_debugged = (info.p_flag & P_TRACED) != 0;
    119 #else
    120   being_debugged = (info.kp_proc.p_flag & P_TRACED) != 0;
    121 #endif
    122   return being_debugged;
    123 }
    124 
    125 #elif defined(OS_LINUX) || defined(OS_ANDROID)
    126 
    127 // We can look in /proc/self/status for TracerPid.  We are likely used in crash
    128 // handling, so we are careful not to use the heap or have side effects.
    129 // Another option that is common is to try to ptrace yourself, but then we
    130 // can't detach without forking(), and that's not so great.
    131 // static
    132 bool BeingDebugged() {
    133   // NOTE: This code MUST be async-signal safe (it's used by in-process
    134   // stack dumping signal handler). NO malloc or stdio is allowed here.
    135 
    136   int status_fd = open("/proc/self/status", O_RDONLY);
    137   if (status_fd == -1)
    138     return false;
    139 
    140   // We assume our line will be in the first 1024 characters and that we can
    141   // read this much all at once.  In practice this will generally be true.
    142   // This simplifies and speeds up things considerably.
    143   char buf[1024];
    144 
    145   ssize_t num_read = HANDLE_EINTR(read(status_fd, buf, sizeof(buf)));
    146   if (IGNORE_EINTR(close(status_fd)) < 0)
    147     return false;
    148 
    149   if (num_read <= 0)
    150     return false;
    151 
    152   StringPiece status(buf, num_read);
    153   StringPiece tracer("TracerPid:\t");
    154 
    155   StringPiece::size_type pid_index = status.find(tracer);
    156   if (pid_index == StringPiece::npos)
    157     return false;
    158 
    159   // Our pid is 0 without a debugger, assume this for any pid starting with 0.
    160   pid_index += tracer.size();
    161   return pid_index < status.size() && status[pid_index] != '0';
    162 }
    163 
    164 #else
    165 
    166 bool BeingDebugged() {
    167   NOTIMPLEMENTED();
    168   return false;
    169 }
    170 
    171 #endif
    172 
    173 // We want to break into the debugger in Debug mode, and cause a crash dump in
    174 // Release mode. Breakpad behaves as follows:
    175 //
    176 // +-------+-----------------+-----------------+
    177 // | OS    | Dump on SIGTRAP | Dump on SIGABRT |
    178 // +-------+-----------------+-----------------+
    179 // | Linux |       N         |        Y        |
    180 // | Mac   |       Y         |        N        |
    181 // +-------+-----------------+-----------------+
    182 //
    183 // Thus we do the following:
    184 // Linux: Debug mode if a debugger is attached, send SIGTRAP; otherwise send
    185 //        SIGABRT
    186 // Mac: Always send SIGTRAP.
    187 
    188 #if defined(ARCH_CPU_ARMEL)
    189 #define DEBUG_BREAK_ASM() asm("bkpt 0")
    190 #elif defined(ARCH_CPU_ARM64)
    191 #define DEBUG_BREAK_ASM() asm("brk 0")
    192 #elif defined(ARCH_CPU_MIPS_FAMILY)
    193 #define DEBUG_BREAK_ASM() asm("break 2")
    194 #elif defined(ARCH_CPU_X86_FAMILY)
    195 #define DEBUG_BREAK_ASM() asm("int3")
    196 #endif
    197 
    198 #if defined(NDEBUG) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
    199 #define DEBUG_BREAK() abort()
    200 #elif defined(OS_NACL)
    201 // The NaCl verifier doesn't let use use int3.  For now, we call abort().  We
    202 // should ask for advice from some NaCl experts about the optimum thing here.
    203 // http://code.google.com/p/nativeclient/issues/detail?id=645
    204 #define DEBUG_BREAK() abort()
    205 #elif !defined(OS_MACOSX)
    206 // Though Android has a "helpful" process called debuggerd to catch native
    207 // signals on the general assumption that they are fatal errors. If no debugger
    208 // is attached, we call abort since Breakpad needs SIGABRT to create a dump.
    209 // When debugger is attached, for ARM platform the bkpt instruction appears
    210 // to cause SIGBUS which is trapped by debuggerd, and we've had great
    211 // difficulty continuing in a debugger once we stop from SIG triggered by native
    212 // code, use GDB to set |go| to 1 to resume execution; for X86 platform, use
    213 // "int3" to setup breakpiont and raise SIGTRAP.
    214 //
    215 // On other POSIX architectures, except Mac OS X, we use the same logic to
    216 // ensure that breakpad creates a dump on crashes while it is still possible to
    217 // use a debugger.
    218 namespace {
    219 void DebugBreak() {
    220   if (!BeingDebugged()) {
    221     abort();
    222   } else {
    223 #if defined(DEBUG_BREAK_ASM)
    224     DEBUG_BREAK_ASM();
    225 #else
    226     volatile int go = 0;
    227     while (!go) {
    228       base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(100));
    229     }
    230 #endif
    231   }
    232 }
    233 }  // namespace
    234 #define DEBUG_BREAK() DebugBreak()
    235 #elif defined(DEBUG_BREAK_ASM)
    236 #define DEBUG_BREAK() DEBUG_BREAK_ASM()
    237 #else
    238 #error "Don't know how to debug break on this architecture/OS"
    239 #endif
    240 
    241 void BreakDebugger() {
    242   // NOTE: This code MUST be async-signal safe (it's used by in-process
    243   // stack dumping signal handler). NO malloc or stdio is allowed here.
    244 
    245   // Linker's ICF feature may merge this function with other functions with the
    246   // same definition (e.g. any function whose sole job is to call abort()) and
    247   // it may confuse the crash report processing system. http://crbug.com/508489
    248   static int static_variable_to_make_this_function_unique = 0;
    249   base::debug::Alias(&static_variable_to_make_this_function_unique);
    250 
    251   DEBUG_BREAK();
    252 #if defined(OS_ANDROID) && !defined(OFFICIAL_BUILD)
    253   // For Android development we always build release (debug builds are
    254   // unmanageably large), so the unofficial build is used for debugging. It is
    255   // helpful to be able to insert BreakDebugger() statements in the source,
    256   // attach the debugger, inspect the state of the program and then resume it by
    257   // setting the 'go' variable above.
    258 #elif defined(NDEBUG)
    259   // Terminate the program after signaling the debug break.
    260   _exit(1);
    261 #endif
    262 }
    263 
    264 }  // namespace debug
    265 }  // namespace base
    266