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