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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 #ifndef BASE_LOGGING_H_
      6 #define BASE_LOGGING_H_
      7 
      8 #include <stddef.h>
      9 
     10 #include <cassert>
     11 #include <cstring>
     12 #include <sstream>
     13 #include <string>
     14 #include <type_traits>
     15 #include <utility>
     16 
     17 #include "base/base_export.h"
     18 #include "base/callback_forward.h"
     19 #include "base/compiler_specific.h"
     20 #include "base/debug/debugger.h"
     21 #include "base/macros.h"
     22 #include "base/strings/string_piece_forward.h"
     23 #include "base/template_util.h"
     24 #include "build/build_config.h"
     25 
     26 //
     27 // Optional message capabilities
     28 // -----------------------------
     29 // Assertion failed messages and fatal errors are displayed in a dialog box
     30 // before the application exits. However, running this UI creates a message
     31 // loop, which causes application messages to be processed and potentially
     32 // dispatched to existing application windows. Since the application is in a
     33 // bad state when this assertion dialog is displayed, these messages may not
     34 // get processed and hang the dialog, or the application might go crazy.
     35 //
     36 // Therefore, it can be beneficial to display the error dialog in a separate
     37 // process from the main application. When the logging system needs to display
     38 // a fatal error dialog box, it will look for a program called
     39 // "DebugMessage.exe" in the same directory as the application executable. It
     40 // will run this application with the message as the command line, and will
     41 // not include the name of the application as is traditional for easier
     42 // parsing.
     43 //
     44 // The code for DebugMessage.exe is only one line. In WinMain, do:
     45 //   MessageBox(NULL, GetCommandLineW(), L"Fatal Error", 0);
     46 //
     47 // If DebugMessage.exe is not found, the logging code will use a normal
     48 // MessageBox, potentially causing the problems discussed above.
     49 
     50 
     51 // Instructions
     52 // ------------
     53 //
     54 // Make a bunch of macros for logging.  The way to log things is to stream
     55 // things to LOG(<a particular severity level>).  E.g.,
     56 //
     57 //   LOG(INFO) << "Found " << num_cookies << " cookies";
     58 //
     59 // You can also do conditional logging:
     60 //
     61 //   LOG_IF(INFO, num_cookies > 10) << "Got lots of cookies";
     62 //
     63 // The CHECK(condition) macro is active in both debug and release builds and
     64 // effectively performs a LOG(FATAL) which terminates the process and
     65 // generates a crashdump unless a debugger is attached.
     66 //
     67 // There are also "debug mode" logging macros like the ones above:
     68 //
     69 //   DLOG(INFO) << "Found cookies";
     70 //
     71 //   DLOG_IF(INFO, num_cookies > 10) << "Got lots of cookies";
     72 //
     73 // All "debug mode" logging is compiled away to nothing for non-debug mode
     74 // compiles.  LOG_IF and development flags also work well together
     75 // because the code can be compiled away sometimes.
     76 //
     77 // We also have
     78 //
     79 //   LOG_ASSERT(assertion);
     80 //   DLOG_ASSERT(assertion);
     81 //
     82 // which is syntactic sugar for {,D}LOG_IF(FATAL, assert fails) << assertion;
     83 //
     84 // There are "verbose level" logging macros.  They look like
     85 //
     86 //   VLOG(1) << "I'm printed when you run the program with --v=1 or more";
     87 //   VLOG(2) << "I'm printed when you run the program with --v=2 or more";
     88 //
     89 // These always log at the INFO log level (when they log at all).
     90 // The verbose logging can also be turned on module-by-module.  For instance,
     91 //    --vmodule=profile=2,icon_loader=1,browser_*=3,*/chromeos/*=4 --v=0
     92 // will cause:
     93 //   a. VLOG(2) and lower messages to be printed from profile.{h,cc}
     94 //   b. VLOG(1) and lower messages to be printed from icon_loader.{h,cc}
     95 //   c. VLOG(3) and lower messages to be printed from files prefixed with
     96 //      "browser"
     97 //   d. VLOG(4) and lower messages to be printed from files under a
     98 //     "chromeos" directory.
     99 //   e. VLOG(0) and lower messages to be printed from elsewhere
    100 //
    101 // The wildcarding functionality shown by (c) supports both '*' (match
    102 // 0 or more characters) and '?' (match any single character)
    103 // wildcards.  Any pattern containing a forward or backward slash will
    104 // be tested against the whole pathname and not just the module.
    105 // E.g., "*/foo/bar/*=2" would change the logging level for all code
    106 // in source files under a "foo/bar" directory.
    107 //
    108 // There's also VLOG_IS_ON(n) "verbose level" condition macro. To be used as
    109 //
    110 //   if (VLOG_IS_ON(2)) {
    111 //     // do some logging preparation and logging
    112 //     // that can't be accomplished with just VLOG(2) << ...;
    113 //   }
    114 //
    115 // There is also a VLOG_IF "verbose level" condition macro for sample
    116 // cases, when some extra computation and preparation for logs is not
    117 // needed.
    118 //
    119 //   VLOG_IF(1, (size > 1024))
    120 //      << "I'm printed when size is more than 1024 and when you run the "
    121 //         "program with --v=1 or more";
    122 //
    123 // We also override the standard 'assert' to use 'DLOG_ASSERT'.
    124 //
    125 // Lastly, there is:
    126 //
    127 //   PLOG(ERROR) << "Couldn't do foo";
    128 //   DPLOG(ERROR) << "Couldn't do foo";
    129 //   PLOG_IF(ERROR, cond) << "Couldn't do foo";
    130 //   DPLOG_IF(ERROR, cond) << "Couldn't do foo";
    131 //   PCHECK(condition) << "Couldn't do foo";
    132 //   DPCHECK(condition) << "Couldn't do foo";
    133 //
    134 // which append the last system error to the message in string form (taken from
    135 // GetLastError() on Windows and errno on POSIX).
    136 //
    137 // The supported severity levels for macros that allow you to specify one
    138 // are (in increasing order of severity) INFO, WARNING, ERROR, and FATAL.
    139 //
    140 // Very important: logging a message at the FATAL severity level causes
    141 // the program to terminate (after the message is logged).
    142 //
    143 // There is the special severity of DFATAL, which logs FATAL in debug mode,
    144 // ERROR in normal mode.
    145 
    146 namespace logging {
    147 
    148 // TODO(avi): do we want to do a unification of character types here?
    149 #if defined(OS_WIN)
    150 typedef wchar_t PathChar;
    151 #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
    152 typedef char PathChar;
    153 #endif
    154 
    155 // Where to record logging output? A flat file and/or system debug log
    156 // via OutputDebugString.
    157 enum LoggingDestination {
    158   LOG_NONE                = 0,
    159   LOG_TO_FILE             = 1 << 0,
    160   LOG_TO_SYSTEM_DEBUG_LOG = 1 << 1,
    161 
    162   LOG_TO_ALL = LOG_TO_FILE | LOG_TO_SYSTEM_DEBUG_LOG,
    163 
    164   // On Windows, use a file next to the exe; on POSIX platforms, where
    165   // it may not even be possible to locate the executable on disk, use
    166   // stderr.
    167 #if defined(OS_WIN)
    168   LOG_DEFAULT = LOG_TO_FILE,
    169 #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
    170   LOG_DEFAULT = LOG_TO_SYSTEM_DEBUG_LOG,
    171 #endif
    172 };
    173 
    174 // Indicates that the log file should be locked when being written to.
    175 // Unless there is only one single-threaded process that is logging to
    176 // the log file, the file should be locked during writes to make each
    177 // log output atomic. Other writers will block.
    178 //
    179 // All processes writing to the log file must have their locking set for it to
    180 // work properly. Defaults to LOCK_LOG_FILE.
    181 enum LogLockingState { LOCK_LOG_FILE, DONT_LOCK_LOG_FILE };
    182 
    183 // On startup, should we delete or append to an existing log file (if any)?
    184 // Defaults to APPEND_TO_OLD_LOG_FILE.
    185 enum OldFileDeletionState { DELETE_OLD_LOG_FILE, APPEND_TO_OLD_LOG_FILE };
    186 
    187 struct BASE_EXPORT LoggingSettings {
    188   // The defaults values are:
    189   //
    190   //  logging_dest: LOG_DEFAULT
    191   //  log_file:     NULL
    192   //  lock_log:     LOCK_LOG_FILE
    193   //  delete_old:   APPEND_TO_OLD_LOG_FILE
    194   LoggingSettings();
    195 
    196   LoggingDestination logging_dest;
    197 
    198   // The three settings below have an effect only when LOG_TO_FILE is
    199   // set in |logging_dest|.
    200   const PathChar* log_file;
    201   LogLockingState lock_log;
    202   OldFileDeletionState delete_old;
    203 };
    204 
    205 // Define different names for the BaseInitLoggingImpl() function depending on
    206 // whether NDEBUG is defined or not so that we'll fail to link if someone tries
    207 // to compile logging.cc with NDEBUG but includes logging.h without defining it,
    208 // or vice versa.
    209 #if defined(NDEBUG)
    210 #define BaseInitLoggingImpl BaseInitLoggingImpl_built_with_NDEBUG
    211 #else
    212 #define BaseInitLoggingImpl BaseInitLoggingImpl_built_without_NDEBUG
    213 #endif
    214 
    215 // Implementation of the InitLogging() method declared below.  We use a
    216 // more-specific name so we can #define it above without affecting other code
    217 // that has named stuff "InitLogging".
    218 BASE_EXPORT bool BaseInitLoggingImpl(const LoggingSettings& settings);
    219 
    220 // Sets the log file name and other global logging state. Calling this function
    221 // is recommended, and is normally done at the beginning of application init.
    222 // If you don't call it, all the flags will be initialized to their default
    223 // values, and there is a race condition that may leak a critical section
    224 // object if two threads try to do the first log at the same time.
    225 // See the definition of the enums above for descriptions and default values.
    226 //
    227 // The default log file is initialized to "debug.log" in the application
    228 // directory. You probably don't want this, especially since the program
    229 // directory may not be writable on an enduser's system.
    230 //
    231 // This function may be called a second time to re-direct logging (e.g after
    232 // loging in to a user partition), however it should never be called more than
    233 // twice.
    234 inline bool InitLogging(const LoggingSettings& settings) {
    235   return BaseInitLoggingImpl(settings);
    236 }
    237 
    238 // Sets the log level. Anything at or above this level will be written to the
    239 // log file/displayed to the user (if applicable). Anything below this level
    240 // will be silently ignored. The log level defaults to 0 (everything is logged
    241 // up to level INFO) if this function is not called.
    242 // Note that log messages for VLOG(x) are logged at level -x, so setting
    243 // the min log level to negative values enables verbose logging.
    244 BASE_EXPORT void SetMinLogLevel(int level);
    245 
    246 // Gets the current log level.
    247 BASE_EXPORT int GetMinLogLevel();
    248 
    249 // Used by LOG_IS_ON to lazy-evaluate stream arguments.
    250 BASE_EXPORT bool ShouldCreateLogMessage(int severity);
    251 
    252 // Gets the VLOG default verbosity level.
    253 BASE_EXPORT int GetVlogVerbosity();
    254 
    255 // Note that |N| is the size *with* the null terminator.
    256 BASE_EXPORT int GetVlogLevelHelper(const char* file_start, size_t N);
    257 
    258 // Gets the current vlog level for the given file (usually taken from __FILE__).
    259 template <size_t N>
    260 int GetVlogLevel(const char (&file)[N]) {
    261   return GetVlogLevelHelper(file, N);
    262 }
    263 
    264 // Sets the common items you want to be prepended to each log message.
    265 // process and thread IDs default to off, the timestamp defaults to on.
    266 // If this function is not called, logging defaults to writing the timestamp
    267 // only.
    268 BASE_EXPORT void SetLogItems(bool enable_process_id, bool enable_thread_id,
    269                              bool enable_timestamp, bool enable_tickcount);
    270 
    271 // Sets whether or not you'd like to see fatal debug messages popped up in
    272 // a dialog box or not.
    273 // Dialogs are not shown by default.
    274 BASE_EXPORT void SetShowErrorDialogs(bool enable_dialogs);
    275 
    276 // Sets the Log Assert Handler that will be used to notify of check failures.
    277 // Resets Log Assert Handler on object destruction.
    278 // The default handler shows a dialog box and then terminate the process,
    279 // however clients can use this function to override with their own handling
    280 // (e.g. a silent one for Unit Tests)
    281 using LogAssertHandlerFunction =
    282     base::Callback<void(const char* file,
    283                         int line,
    284                         const base::StringPiece message,
    285                         const base::StringPiece stack_trace)>;
    286 
    287 class BASE_EXPORT ScopedLogAssertHandler {
    288  public:
    289   explicit ScopedLogAssertHandler(LogAssertHandlerFunction handler);
    290   ~ScopedLogAssertHandler();
    291 
    292  private:
    293   DISALLOW_COPY_AND_ASSIGN(ScopedLogAssertHandler);
    294 };
    295 
    296 // Sets the Log Message Handler that gets passed every log message before
    297 // it's sent to other log destinations (if any).
    298 // Returns true to signal that it handled the message and the message
    299 // should not be sent to other log destinations.
    300 typedef bool (*LogMessageHandlerFunction)(int severity,
    301     const char* file, int line, size_t message_start, const std::string& str);
    302 BASE_EXPORT void SetLogMessageHandler(LogMessageHandlerFunction handler);
    303 BASE_EXPORT LogMessageHandlerFunction GetLogMessageHandler();
    304 
    305 // The ANALYZER_ASSUME_TRUE(bool arg) macro adds compiler-specific hints
    306 // to Clang which control what code paths are statically analyzed,
    307 // and is meant to be used in conjunction with assert & assert-like functions.
    308 // The expression is passed straight through if analysis isn't enabled.
    309 //
    310 // ANALYZER_SKIP_THIS_PATH() suppresses static analysis for the current
    311 // codepath and any other branching codepaths that might follow.
    312 #if defined(__clang_analyzer__)
    313 
    314 inline constexpr bool AnalyzerNoReturn() __attribute__((analyzer_noreturn)) {
    315   return false;
    316 }
    317 
    318 inline constexpr bool AnalyzerAssumeTrue(bool arg) {
    319   // AnalyzerNoReturn() is invoked and analysis is terminated if |arg| is
    320   // false.
    321   return arg || AnalyzerNoReturn();
    322 }
    323 
    324 #define ANALYZER_ASSUME_TRUE(arg) logging::AnalyzerAssumeTrue(!!(arg))
    325 #define ANALYZER_SKIP_THIS_PATH() \
    326   static_cast<void>(::logging::AnalyzerNoReturn())
    327 #define ANALYZER_ALLOW_UNUSED(var) static_cast<void>(var);
    328 
    329 #else  // !defined(__clang_analyzer__)
    330 
    331 #define ANALYZER_ASSUME_TRUE(arg) (arg)
    332 #define ANALYZER_SKIP_THIS_PATH()
    333 #define ANALYZER_ALLOW_UNUSED(var) static_cast<void>(var);
    334 
    335 #endif  // defined(__clang_analyzer__)
    336 
    337 typedef int LogSeverity;
    338 const LogSeverity LOG_VERBOSE = -1;  // This is level 1 verbosity
    339 // Note: the log severities are used to index into the array of names,
    340 // see log_severity_names.
    341 const LogSeverity LOG_INFO = 0;
    342 const LogSeverity LOG_WARNING = 1;
    343 const LogSeverity LOG_ERROR = 2;
    344 const LogSeverity LOG_FATAL = 3;
    345 const LogSeverity LOG_NUM_SEVERITIES = 4;
    346 
    347 // LOG_DFATAL is LOG_FATAL in debug mode, ERROR in normal mode
    348 #if defined(NDEBUG)
    349 const LogSeverity LOG_DFATAL = LOG_ERROR;
    350 #else
    351 const LogSeverity LOG_DFATAL = LOG_FATAL;
    352 #endif
    353 
    354 // A few definitions of macros that don't generate much code. These are used
    355 // by LOG() and LOG_IF, etc. Since these are used all over our code, it's
    356 // better to have compact code for these operations.
    357 #define COMPACT_GOOGLE_LOG_EX_INFO(ClassName, ...) \
    358   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOG_INFO, ##__VA_ARGS__)
    359 #define COMPACT_GOOGLE_LOG_EX_WARNING(ClassName, ...)              \
    360   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOG_WARNING, \
    361                        ##__VA_ARGS__)
    362 #define COMPACT_GOOGLE_LOG_EX_ERROR(ClassName, ...) \
    363   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOG_ERROR, ##__VA_ARGS__)
    364 #define COMPACT_GOOGLE_LOG_EX_FATAL(ClassName, ...) \
    365   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOG_FATAL, ##__VA_ARGS__)
    366 #define COMPACT_GOOGLE_LOG_EX_DFATAL(ClassName, ...) \
    367   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOG_DFATAL, ##__VA_ARGS__)
    368 #define COMPACT_GOOGLE_LOG_EX_DCHECK(ClassName, ...) \
    369   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOG_DCHECK, ##__VA_ARGS__)
    370 
    371 #define COMPACT_GOOGLE_LOG_INFO COMPACT_GOOGLE_LOG_EX_INFO(LogMessage)
    372 #define COMPACT_GOOGLE_LOG_WARNING COMPACT_GOOGLE_LOG_EX_WARNING(LogMessage)
    373 #define COMPACT_GOOGLE_LOG_ERROR COMPACT_GOOGLE_LOG_EX_ERROR(LogMessage)
    374 #define COMPACT_GOOGLE_LOG_FATAL COMPACT_GOOGLE_LOG_EX_FATAL(LogMessage)
    375 #define COMPACT_GOOGLE_LOG_DFATAL COMPACT_GOOGLE_LOG_EX_DFATAL(LogMessage)
    376 #define COMPACT_GOOGLE_LOG_DCHECK COMPACT_GOOGLE_LOG_EX_DCHECK(LogMessage)
    377 
    378 #if defined(OS_WIN)
    379 // wingdi.h defines ERROR to be 0. When we call LOG(ERROR), it gets
    380 // substituted with 0, and it expands to COMPACT_GOOGLE_LOG_0. To allow us
    381 // to keep using this syntax, we define this macro to do the same thing
    382 // as COMPACT_GOOGLE_LOG_ERROR, and also define ERROR the same way that
    383 // the Windows SDK does for consistency.
    384 #define ERROR 0
    385 #define COMPACT_GOOGLE_LOG_EX_0(ClassName, ...) \
    386   COMPACT_GOOGLE_LOG_EX_ERROR(ClassName , ##__VA_ARGS__)
    387 #define COMPACT_GOOGLE_LOG_0 COMPACT_GOOGLE_LOG_ERROR
    388 // Needed for LOG_IS_ON(ERROR).
    389 const LogSeverity LOG_0 = LOG_ERROR;
    390 #endif
    391 
    392 // As special cases, we can assume that LOG_IS_ON(FATAL) always holds. Also,
    393 // LOG_IS_ON(DFATAL) always holds in debug mode. In particular, CHECK()s will
    394 // always fire if they fail.
    395 #define LOG_IS_ON(severity) \
    396   (::logging::ShouldCreateLogMessage(::logging::LOG_##severity))
    397 
    398 // We can't do any caching tricks with VLOG_IS_ON() like the
    399 // google-glog version since it requires GCC extensions.  This means
    400 // that using the v-logging functions in conjunction with --vmodule
    401 // may be slow.
    402 #define VLOG_IS_ON(verboselevel) \
    403   ((verboselevel) <= ::logging::GetVlogLevel(__FILE__))
    404 
    405 // Helper macro which avoids evaluating the arguments to a stream if
    406 // the condition doesn't hold. Condition is evaluated once and only once.
    407 #define LAZY_STREAM(stream, condition)                                  \
    408   !(condition) ? (void) 0 : ::logging::LogMessageVoidify() & (stream)
    409 
    410 // We use the preprocessor's merging operator, "##", so that, e.g.,
    411 // LOG(INFO) becomes the token COMPACT_GOOGLE_LOG_INFO.  There's some funny
    412 // subtle difference between ostream member streaming functions (e.g.,
    413 // ostream::operator<<(int) and ostream non-member streaming functions
    414 // (e.g., ::operator<<(ostream&, string&): it turns out that it's
    415 // impossible to stream something like a string directly to an unnamed
    416 // ostream. We employ a neat hack by calling the stream() member
    417 // function of LogMessage which seems to avoid the problem.
    418 #define LOG_STREAM(severity) COMPACT_GOOGLE_LOG_ ## severity.stream()
    419 
    420 #define LOG(severity) LAZY_STREAM(LOG_STREAM(severity), LOG_IS_ON(severity))
    421 #define LOG_IF(severity, condition) \
    422   LAZY_STREAM(LOG_STREAM(severity), LOG_IS_ON(severity) && (condition))
    423 
    424 // The VLOG macros log with negative verbosities.
    425 #define VLOG_STREAM(verbose_level) \
    426   ::logging::LogMessage(__FILE__, __LINE__, -verbose_level).stream()
    427 
    428 #define VLOG(verbose_level) \
    429   LAZY_STREAM(VLOG_STREAM(verbose_level), VLOG_IS_ON(verbose_level))
    430 
    431 #define VLOG_IF(verbose_level, condition) \
    432   LAZY_STREAM(VLOG_STREAM(verbose_level), \
    433       VLOG_IS_ON(verbose_level) && (condition))
    434 
    435 #if defined (OS_WIN)
    436 #define VPLOG_STREAM(verbose_level) \
    437   ::logging::Win32ErrorLogMessage(__FILE__, __LINE__, -verbose_level, \
    438     ::logging::GetLastSystemErrorCode()).stream()
    439 #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
    440 #define VPLOG_STREAM(verbose_level) \
    441   ::logging::ErrnoLogMessage(__FILE__, __LINE__, -verbose_level, \
    442     ::logging::GetLastSystemErrorCode()).stream()
    443 #endif
    444 
    445 #define VPLOG(verbose_level) \
    446   LAZY_STREAM(VPLOG_STREAM(verbose_level), VLOG_IS_ON(verbose_level))
    447 
    448 #define VPLOG_IF(verbose_level, condition) \
    449   LAZY_STREAM(VPLOG_STREAM(verbose_level), \
    450     VLOG_IS_ON(verbose_level) && (condition))
    451 
    452 // TODO(akalin): Add more VLOG variants, e.g. VPLOG.
    453 
    454 #define LOG_ASSERT(condition)                       \
    455   LOG_IF(FATAL, !(ANALYZER_ASSUME_TRUE(condition))) \
    456       << "Assert failed: " #condition ". "
    457 
    458 #if defined(OS_WIN)
    459 #define PLOG_STREAM(severity) \
    460   COMPACT_GOOGLE_LOG_EX_ ## severity(Win32ErrorLogMessage, \
    461       ::logging::GetLastSystemErrorCode()).stream()
    462 #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
    463 #define PLOG_STREAM(severity) \
    464   COMPACT_GOOGLE_LOG_EX_ ## severity(ErrnoLogMessage, \
    465       ::logging::GetLastSystemErrorCode()).stream()
    466 #endif
    467 
    468 #define PLOG(severity)                                          \
    469   LAZY_STREAM(PLOG_STREAM(severity), LOG_IS_ON(severity))
    470 
    471 #define PLOG_IF(severity, condition) \
    472   LAZY_STREAM(PLOG_STREAM(severity), LOG_IS_ON(severity) && (condition))
    473 
    474 BASE_EXPORT extern std::ostream* g_swallow_stream;
    475 
    476 // Note that g_swallow_stream is used instead of an arbitrary LOG() stream to
    477 // avoid the creation of an object with a non-trivial destructor (LogMessage).
    478 // On MSVC x86 (checked on 2015 Update 3), this causes a few additional
    479 // pointless instructions to be emitted even at full optimization level, even
    480 // though the : arm of the ternary operator is clearly never executed. Using a
    481 // simpler object to be &'d with Voidify() avoids these extra instructions.
    482 // Using a simpler POD object with a templated operator<< also works to avoid
    483 // these instructions. However, this causes warnings on statically defined
    484 // implementations of operator<<(std::ostream, ...) in some .cc files, because
    485 // they become defined-but-unreferenced functions. A reinterpret_cast of 0 to an
    486 // ostream* also is not suitable, because some compilers warn of undefined
    487 // behavior.
    488 #define EAT_STREAM_PARAMETERS \
    489   true ? (void)0              \
    490        : ::logging::LogMessageVoidify() & (*::logging::g_swallow_stream)
    491 
    492 // Captures the result of a CHECK_EQ (for example) and facilitates testing as a
    493 // boolean.
    494 class CheckOpResult {
    495  public:
    496   // |message| must be non-null if and only if the check failed.
    497   CheckOpResult(std::string* message) : message_(message) {}
    498   // Returns true if the check succeeded.
    499   operator bool() const { return !message_; }
    500   // Returns the message.
    501   std::string* message() { return message_; }
    502 
    503  private:
    504   std::string* message_;
    505 };
    506 
    507 // Crashes in the fastest possible way with no attempt at logging.
    508 // There are different constraints to satisfy here, see http://crbug.com/664209
    509 // for more context:
    510 // - The trap instructions, and hence the PC value at crash time, have to be
    511 //   distinct and not get folded into the same opcode by the compiler.
    512 //   On Linux/Android this is tricky because GCC still folds identical
    513 //   asm volatile blocks. The workaround is generating distinct opcodes for
    514 //   each CHECK using the __COUNTER__ macro.
    515 // - The debug info for the trap instruction has to be attributed to the source
    516 //   line that has the CHECK(), to make crash reports actionable. This rules
    517 //   out the ability of using a inline function, at least as long as clang
    518 //   doesn't support attribute(artificial).
    519 // - Failed CHECKs should produce a signal that is distinguishable from an
    520 //   invalid memory access, to improve the actionability of crash reports.
    521 // - The compiler should treat the CHECK as no-return instructions, so that the
    522 //   trap code can be efficiently packed in the prologue of the function and
    523 //   doesn't interfere with the main execution flow.
    524 // - When debugging, developers shouldn't be able to accidentally step over a
    525 //   CHECK. This is achieved by putting opcodes that will cause a non
    526 //   continuable exception after the actual trap instruction.
    527 // - Don't cause too much binary bloat.
    528 #if defined(COMPILER_GCC)
    529 
    530 #if defined(ARCH_CPU_X86_FAMILY) && !defined(OS_NACL)
    531 // int 3 will generate a SIGTRAP.
    532 #define TRAP_SEQUENCE() \
    533   asm volatile(         \
    534       "int3; ud2; push %0;" ::"i"(static_cast<unsigned char>(__COUNTER__)))
    535 
    536 #elif defined(ARCH_CPU_ARMEL) && !defined(OS_NACL)
    537 // bkpt will generate a SIGBUS when running on armv7 and a SIGTRAP when running
    538 // as a 32 bit userspace app on arm64. There doesn't seem to be any way to
    539 // cause a SIGTRAP from userspace without using a syscall (which would be a
    540 // problem for sandboxing).
    541 #define TRAP_SEQUENCE() \
    542   asm volatile("bkpt #0; udf %0;" ::"i"(__COUNTER__ % 256))
    543 
    544 #elif defined(ARCH_CPU_ARM64) && !defined(OS_NACL)
    545 // This will always generate a SIGTRAP on arm64.
    546 #define TRAP_SEQUENCE() \
    547   asm volatile("brk #0; hlt %0;" ::"i"(__COUNTER__ % 65536))
    548 
    549 #else
    550 // Crash report accuracy will not be guaranteed on other architectures, but at
    551 // least this will crash as expected.
    552 #define TRAP_SEQUENCE() __builtin_trap()
    553 #endif  // ARCH_CPU_*
    554 
    555 // CHECK() and the trap sequence can be invoked from a constexpr function.
    556 // This could make compilation fail on GCC, as it forbids directly using inline
    557 // asm inside a constexpr function. However, it allows calling a lambda
    558 // expression including the same asm.
    559 // The side effect is that the top of the stacktrace will not point to the
    560 // calling function, but to this anonymous lambda. This is still useful as the
    561 // full name of the lambda will typically include the name of the function that
    562 // calls CHECK() and the debugger will still break at the right line of code.
    563 #if !defined(__clang__)
    564 #define WRAPPED_TRAP_SEQUENCE() \
    565   do {                          \
    566     [] { TRAP_SEQUENCE(); }();  \
    567   } while (false)
    568 #else
    569 #define WRAPPED_TRAP_SEQUENCE() TRAP_SEQUENCE()
    570 #endif
    571 
    572 #define IMMEDIATE_CRASH()    \
    573   ({                         \
    574     WRAPPED_TRAP_SEQUENCE(); \
    575     __builtin_unreachable(); \
    576   })
    577 
    578 #elif defined(COMPILER_MSVC)
    579 
    580 // Clang is cleverer about coalescing int3s, so we need to add a unique-ish
    581 // instruction following the __debugbreak() to have it emit distinct locations
    582 // for CHECKs rather than collapsing them all together. It would be nice to use
    583 // a short intrinsic to do this (and perhaps have only one implementation for
    584 // both clang and MSVC), however clang-cl currently does not support intrinsics.
    585 // On the flip side, MSVC x64 doesn't support inline asm. So, we have to have
    586 // two implementations. Normally clang-cl's version will be 5 bytes (1 for
    587 // `int3`, 2 for `ud2`, 2 for `push byte imm`, however, TODO(scottmg):
    588 // https://crbug.com/694670 clang-cl doesn't currently support %'ing
    589 // __COUNTER__, so eventually it will emit the dword form of push.
    590 // TODO(scottmg): Reinvestigate a short sequence that will work on both
    591 // compilers once clang supports more intrinsics. See https://crbug.com/693713.
    592 #if defined(__clang__)
    593 #define IMMEDIATE_CRASH()                           \
    594   ({                                                \
    595     {__asm int 3 __asm ud2 __asm push __COUNTER__}; \
    596     __builtin_unreachable();                        \
    597   })
    598 #else
    599 #define IMMEDIATE_CRASH() __debugbreak()
    600 #endif  // __clang__
    601 
    602 #else
    603 #error Port
    604 #endif
    605 
    606 // CHECK dies with a fatal error if condition is not true.  It is *not*
    607 // controlled by NDEBUG, so the check will be executed regardless of
    608 // compilation mode.
    609 //
    610 // We make sure CHECK et al. always evaluates their arguments, as
    611 // doing CHECK(FunctionWithSideEffect()) is a common idiom.
    612 
    613 #if defined(OFFICIAL_BUILD) && defined(NDEBUG)
    614 
    615 // Make all CHECK functions discard their log strings to reduce code bloat, and
    616 // improve performance, for official release builds.
    617 //
    618 // This is not calling BreakDebugger since this is called frequently, and
    619 // calling an out-of-line function instead of a noreturn inline macro prevents
    620 // compiler optimizations.
    621 #define CHECK(condition) \
    622   UNLIKELY(!(condition)) ? IMMEDIATE_CRASH() : EAT_STREAM_PARAMETERS
    623 
    624 // PCHECK includes the system error code, which is useful for determining
    625 // why the condition failed. In official builds, preserve only the error code
    626 // message so that it is available in crash reports. The stringified
    627 // condition and any additional stream parameters are dropped.
    628 #define PCHECK(condition)                                  \
    629   LAZY_STREAM(PLOG_STREAM(FATAL), UNLIKELY(!(condition))); \
    630   EAT_STREAM_PARAMETERS
    631 
    632 #define CHECK_OP(name, op, val1, val2) CHECK((val1) op (val2))
    633 
    634 #else  // !(OFFICIAL_BUILD && NDEBUG)
    635 
    636 #if defined(_PREFAST_) && defined(OS_WIN)
    637 // Use __analysis_assume to tell the VC++ static analysis engine that
    638 // assert conditions are true, to suppress warnings.  The LAZY_STREAM
    639 // parameter doesn't reference 'condition' in /analyze builds because
    640 // this evaluation confuses /analyze. The !! before condition is because
    641 // __analysis_assume gets confused on some conditions:
    642 // http://randomascii.wordpress.com/2011/09/13/analyze-for-visual-studio-the-ugly-part-5/
    643 
    644 #define CHECK(condition)                    \
    645   __analysis_assume(!!(condition)),         \
    646       LAZY_STREAM(LOG_STREAM(FATAL), false) \
    647           << "Check failed: " #condition ". "
    648 
    649 #define PCHECK(condition)                    \
    650   __analysis_assume(!!(condition)),          \
    651       LAZY_STREAM(PLOG_STREAM(FATAL), false) \
    652           << "Check failed: " #condition ". "
    653 
    654 #else  // _PREFAST_
    655 
    656 // Do as much work as possible out of line to reduce inline code size.
    657 #define CHECK(condition)                                                      \
    658   LAZY_STREAM(::logging::LogMessage(__FILE__, __LINE__, #condition).stream(), \
    659               !ANALYZER_ASSUME_TRUE(condition))
    660 
    661 #define PCHECK(condition)                                           \
    662   LAZY_STREAM(PLOG_STREAM(FATAL), !ANALYZER_ASSUME_TRUE(condition)) \
    663       << "Check failed: " #condition ". "
    664 
    665 #endif  // _PREFAST_
    666 
    667 // Helper macro for binary operators.
    668 // Don't use this macro directly in your code, use CHECK_EQ et al below.
    669 // The 'switch' is used to prevent the 'else' from being ambiguous when the
    670 // macro is used in an 'if' clause such as:
    671 // if (a == 1)
    672 //   CHECK_EQ(2, a);
    673 #define CHECK_OP(name, op, val1, val2)                                         \
    674   switch (0) case 0: default:                                                  \
    675   if (::logging::CheckOpResult true_if_passed =                                \
    676       ::logging::Check##name##Impl((val1), (val2),                             \
    677                                    #val1 " " #op " " #val2))                   \
    678    ;                                                                           \
    679   else                                                                         \
    680     ::logging::LogMessage(__FILE__, __LINE__, true_if_passed.message()).stream()
    681 
    682 #endif  // !(OFFICIAL_BUILD && NDEBUG)
    683 
    684 // This formats a value for a failing CHECK_XX statement.  Ordinarily,
    685 // it uses the definition for operator<<, with a few special cases below.
    686 template <typename T>
    687 inline typename std::enable_if<
    688     base::internal::SupportsOstreamOperator<const T&>::value &&
    689         !std::is_function<typename std::remove_pointer<T>::type>::value,
    690     void>::type
    691 MakeCheckOpValueString(std::ostream* os, const T& v) {
    692   (*os) << v;
    693 }
    694 
    695 // Provide an overload for functions and function pointers. Function pointers
    696 // don't implicitly convert to void* but do implicitly convert to bool, so
    697 // without this function pointers are always printed as 1 or 0. (MSVC isn't
    698 // standards-conforming here and converts function pointers to regular
    699 // pointers, so this is a no-op for MSVC.)
    700 template <typename T>
    701 inline typename std::enable_if<
    702     std::is_function<typename std::remove_pointer<T>::type>::value,
    703     void>::type
    704 MakeCheckOpValueString(std::ostream* os, const T& v) {
    705   (*os) << reinterpret_cast<const void*>(v);
    706 }
    707 
    708 // We need overloads for enums that don't support operator<<.
    709 // (i.e. scoped enums where no operator<< overload was declared).
    710 template <typename T>
    711 inline typename std::enable_if<
    712     !base::internal::SupportsOstreamOperator<const T&>::value &&
    713         std::is_enum<T>::value,
    714     void>::type
    715 MakeCheckOpValueString(std::ostream* os, const T& v) {
    716   (*os) << static_cast<typename std::underlying_type<T>::type>(v);
    717 }
    718 
    719 // We need an explicit overload for std::nullptr_t.
    720 BASE_EXPORT void MakeCheckOpValueString(std::ostream* os, std::nullptr_t p);
    721 
    722 // Build the error message string.  This is separate from the "Impl"
    723 // function template because it is not performance critical and so can
    724 // be out of line, while the "Impl" code should be inline.  Caller
    725 // takes ownership of the returned string.
    726 template<class t1, class t2>
    727 std::string* MakeCheckOpString(const t1& v1, const t2& v2, const char* names) {
    728   std::ostringstream ss;
    729   ss << names << " (";
    730   MakeCheckOpValueString(&ss, v1);
    731   ss << " vs. ";
    732   MakeCheckOpValueString(&ss, v2);
    733   ss << ")";
    734   std::string* msg = new std::string(ss.str());
    735   return msg;
    736 }
    737 
    738 // Commonly used instantiations of MakeCheckOpString<>. Explicitly instantiated
    739 // in logging.cc.
    740 extern template BASE_EXPORT std::string* MakeCheckOpString<int, int>(
    741     const int&, const int&, const char* names);
    742 extern template BASE_EXPORT
    743 std::string* MakeCheckOpString<unsigned long, unsigned long>(
    744     const unsigned long&, const unsigned long&, const char* names);
    745 extern template BASE_EXPORT
    746 std::string* MakeCheckOpString<unsigned long, unsigned int>(
    747     const unsigned long&, const unsigned int&, const char* names);
    748 extern template BASE_EXPORT
    749 std::string* MakeCheckOpString<unsigned int, unsigned long>(
    750     const unsigned int&, const unsigned long&, const char* names);
    751 extern template BASE_EXPORT
    752 std::string* MakeCheckOpString<std::string, std::string>(
    753     const std::string&, const std::string&, const char* name);
    754 
    755 // Helper functions for CHECK_OP macro.
    756 // The (int, int) specialization works around the issue that the compiler
    757 // will not instantiate the template version of the function on values of
    758 // unnamed enum type - see comment below.
    759 //
    760 // The checked condition is wrapped with ANALYZER_ASSUME_TRUE, which under
    761 // static analysis builds, blocks analysis of the current path if the
    762 // condition is false.
    763 #define DEFINE_CHECK_OP_IMPL(name, op)                                       \
    764   template <class t1, class t2>                                              \
    765   inline std::string* Check##name##Impl(const t1& v1, const t2& v2,          \
    766                                         const char* names) {                 \
    767     if (ANALYZER_ASSUME_TRUE(v1 op v2))                                      \
    768       return NULL;                                                           \
    769     else                                                                     \
    770       return ::logging::MakeCheckOpString(v1, v2, names);                    \
    771   }                                                                          \
    772   inline std::string* Check##name##Impl(int v1, int v2, const char* names) { \
    773     if (ANALYZER_ASSUME_TRUE(v1 op v2))                                      \
    774       return NULL;                                                           \
    775     else                                                                     \
    776       return ::logging::MakeCheckOpString(v1, v2, names);                    \
    777   }
    778 DEFINE_CHECK_OP_IMPL(EQ, ==)
    779 DEFINE_CHECK_OP_IMPL(NE, !=)
    780 DEFINE_CHECK_OP_IMPL(LE, <=)
    781 DEFINE_CHECK_OP_IMPL(LT, < )
    782 DEFINE_CHECK_OP_IMPL(GE, >=)
    783 DEFINE_CHECK_OP_IMPL(GT, > )
    784 #undef DEFINE_CHECK_OP_IMPL
    785 
    786 #define CHECK_EQ(val1, val2) CHECK_OP(EQ, ==, val1, val2)
    787 #define CHECK_NE(val1, val2) CHECK_OP(NE, !=, val1, val2)
    788 #define CHECK_LE(val1, val2) CHECK_OP(LE, <=, val1, val2)
    789 #define CHECK_LT(val1, val2) CHECK_OP(LT, < , val1, val2)
    790 #define CHECK_GE(val1, val2) CHECK_OP(GE, >=, val1, val2)
    791 #define CHECK_GT(val1, val2) CHECK_OP(GT, > , val1, val2)
    792 
    793 #if defined(NDEBUG) && !defined(DCHECK_ALWAYS_ON)
    794 #define DCHECK_IS_ON() 0
    795 #else
    796 #define DCHECK_IS_ON() 1
    797 #endif
    798 
    799 // Definitions for DLOG et al.
    800 
    801 #if DCHECK_IS_ON()
    802 
    803 #define DLOG_IS_ON(severity) LOG_IS_ON(severity)
    804 #define DLOG_IF(severity, condition) LOG_IF(severity, condition)
    805 #define DLOG_ASSERT(condition) LOG_ASSERT(condition)
    806 #define DPLOG_IF(severity, condition) PLOG_IF(severity, condition)
    807 #define DVLOG_IF(verboselevel, condition) VLOG_IF(verboselevel, condition)
    808 #define DVPLOG_IF(verboselevel, condition) VPLOG_IF(verboselevel, condition)
    809 
    810 #else  // DCHECK_IS_ON()
    811 
    812 // If !DCHECK_IS_ON(), we want to avoid emitting any references to |condition|
    813 // (which may reference a variable defined only if DCHECK_IS_ON()).
    814 // Contrast this with DCHECK et al., which has different behavior.
    815 
    816 #define DLOG_IS_ON(severity) false
    817 #define DLOG_IF(severity, condition) EAT_STREAM_PARAMETERS
    818 #define DLOG_ASSERT(condition) EAT_STREAM_PARAMETERS
    819 #define DPLOG_IF(severity, condition) EAT_STREAM_PARAMETERS
    820 #define DVLOG_IF(verboselevel, condition) EAT_STREAM_PARAMETERS
    821 #define DVPLOG_IF(verboselevel, condition) EAT_STREAM_PARAMETERS
    822 
    823 #endif  // DCHECK_IS_ON()
    824 
    825 #define DLOG(severity)                                          \
    826   LAZY_STREAM(LOG_STREAM(severity), DLOG_IS_ON(severity))
    827 
    828 #define DPLOG(severity)                                         \
    829   LAZY_STREAM(PLOG_STREAM(severity), DLOG_IS_ON(severity))
    830 
    831 #define DVLOG(verboselevel) DVLOG_IF(verboselevel, VLOG_IS_ON(verboselevel))
    832 
    833 #define DVPLOG(verboselevel) DVPLOG_IF(verboselevel, VLOG_IS_ON(verboselevel))
    834 
    835 // Definitions for DCHECK et al.
    836 
    837 #if DCHECK_IS_ON()
    838 
    839 #if DCHECK_IS_CONFIGURABLE
    840 BASE_EXPORT extern LogSeverity LOG_DCHECK;
    841 #else
    842 const LogSeverity LOG_DCHECK = LOG_FATAL;
    843 #endif
    844 
    845 #else  // DCHECK_IS_ON()
    846 
    847 // There may be users of LOG_DCHECK that are enabled independently
    848 // of DCHECK_IS_ON(), so default to FATAL logging for those.
    849 const LogSeverity LOG_DCHECK = LOG_FATAL;
    850 
    851 #endif  // DCHECK_IS_ON()
    852 
    853 // DCHECK et al. make sure to reference |condition| regardless of
    854 // whether DCHECKs are enabled; this is so that we don't get unused
    855 // variable warnings if the only use of a variable is in a DCHECK.
    856 // This behavior is different from DLOG_IF et al.
    857 //
    858 // Note that the definition of the DCHECK macros depends on whether or not
    859 // DCHECK_IS_ON() is true. When DCHECK_IS_ON() is false, the macros use
    860 // EAT_STREAM_PARAMETERS to avoid expressions that would create temporaries.
    861 
    862 #if defined(_PREFAST_) && defined(OS_WIN)
    863 // See comments on the previous use of __analysis_assume.
    864 
    865 #define DCHECK(condition)                    \
    866   __analysis_assume(!!(condition)),          \
    867       LAZY_STREAM(LOG_STREAM(DCHECK), false) \
    868           << "Check failed: " #condition ". "
    869 
    870 #define DPCHECK(condition)                    \
    871   __analysis_assume(!!(condition)),           \
    872       LAZY_STREAM(PLOG_STREAM(DCHECK), false) \
    873           << "Check failed: " #condition ". "
    874 
    875 #else  // !(defined(_PREFAST_) && defined(OS_WIN))
    876 
    877 #if DCHECK_IS_ON()
    878 
    879 #define DCHECK(condition)                                           \
    880   LAZY_STREAM(LOG_STREAM(DCHECK), !ANALYZER_ASSUME_TRUE(condition)) \
    881       << "Check failed: " #condition ". "
    882 #define DPCHECK(condition)                                           \
    883   LAZY_STREAM(PLOG_STREAM(DCHECK), !ANALYZER_ASSUME_TRUE(condition)) \
    884       << "Check failed: " #condition ". "
    885 
    886 #else  // DCHECK_IS_ON()
    887 
    888 #define DCHECK(condition) EAT_STREAM_PARAMETERS << !(condition)
    889 #define DPCHECK(condition) EAT_STREAM_PARAMETERS << !(condition)
    890 
    891 #endif  // DCHECK_IS_ON()
    892 
    893 #endif  // defined(_PREFAST_) && defined(OS_WIN)
    894 
    895 // Helper macro for binary operators.
    896 // Don't use this macro directly in your code, use DCHECK_EQ et al below.
    897 // The 'switch' is used to prevent the 'else' from being ambiguous when the
    898 // macro is used in an 'if' clause such as:
    899 // if (a == 1)
    900 //   DCHECK_EQ(2, a);
    901 #if DCHECK_IS_ON()
    902 
    903 #define DCHECK_OP(name, op, val1, val2)                                \
    904   switch (0) case 0: default:                                          \
    905   if (::logging::CheckOpResult true_if_passed =                        \
    906       ::logging::Check##name##Impl((val1), (val2),                     \
    907                                    #val1 " " #op " " #val2))           \
    908    ;                                                                   \
    909   else                                                                 \
    910     ::logging::LogMessage(__FILE__, __LINE__, ::logging::LOG_DCHECK,   \
    911                           true_if_passed.message()).stream()
    912 
    913 #else  // DCHECK_IS_ON()
    914 
    915 // When DCHECKs aren't enabled, DCHECK_OP still needs to reference operator<<
    916 // overloads for |val1| and |val2| to avoid potential compiler warnings about
    917 // unused functions. For the same reason, it also compares |val1| and |val2|
    918 // using |op|.
    919 //
    920 // Note that the contract of DCHECK_EQ, etc is that arguments are only evaluated
    921 // once. Even though |val1| and |val2| appear twice in this version of the macro
    922 // expansion, this is OK, since the expression is never actually evaluated.
    923 #define DCHECK_OP(name, op, val1, val2)                             \
    924   EAT_STREAM_PARAMETERS << (::logging::MakeCheckOpValueString(      \
    925                                 ::logging::g_swallow_stream, val1), \
    926                             ::logging::MakeCheckOpValueString(      \
    927                                 ::logging::g_swallow_stream, val2), \
    928                             (val1)op(val2))
    929 
    930 #endif  // DCHECK_IS_ON()
    931 
    932 // Equality/Inequality checks - compare two values, and log a
    933 // LOG_DCHECK message including the two values when the result is not
    934 // as expected.  The values must have operator<<(ostream, ...)
    935 // defined.
    936 //
    937 // You may append to the error message like so:
    938 //   DCHECK_NE(1, 2) << "The world must be ending!";
    939 //
    940 // We are very careful to ensure that each argument is evaluated exactly
    941 // once, and that anything which is legal to pass as a function argument is
    942 // legal here.  In particular, the arguments may be temporary expressions
    943 // which will end up being destroyed at the end of the apparent statement,
    944 // for example:
    945 //   DCHECK_EQ(string("abc")[1], 'b');
    946 //
    947 // WARNING: These don't compile correctly if one of the arguments is a pointer
    948 // and the other is NULL.  In new code, prefer nullptr instead.  To
    949 // work around this for C++98, simply static_cast NULL to the type of the
    950 // desired pointer.
    951 
    952 #define DCHECK_EQ(val1, val2) DCHECK_OP(EQ, ==, val1, val2)
    953 #define DCHECK_NE(val1, val2) DCHECK_OP(NE, !=, val1, val2)
    954 #define DCHECK_LE(val1, val2) DCHECK_OP(LE, <=, val1, val2)
    955 #define DCHECK_LT(val1, val2) DCHECK_OP(LT, < , val1, val2)
    956 #define DCHECK_GE(val1, val2) DCHECK_OP(GE, >=, val1, val2)
    957 #define DCHECK_GT(val1, val2) DCHECK_OP(GT, > , val1, val2)
    958 
    959 #if !DCHECK_IS_ON() && defined(OS_CHROMEOS)
    960 // Implement logging of NOTREACHED() as a dedicated function to get function
    961 // call overhead down to a minimum.
    962 void LogErrorNotReached(const char* file, int line);
    963 #define NOTREACHED()                                       \
    964   true ? ::logging::LogErrorNotReached(__FILE__, __LINE__) \
    965        : EAT_STREAM_PARAMETERS
    966 #else
    967 #define NOTREACHED() DCHECK(false)
    968 #endif
    969 
    970 // Redefine the standard assert to use our nice log files
    971 #undef assert
    972 #define assert(x) DLOG_ASSERT(x)
    973 
    974 // This class more or less represents a particular log message.  You
    975 // create an instance of LogMessage and then stream stuff to it.
    976 // When you finish streaming to it, ~LogMessage is called and the
    977 // full message gets streamed to the appropriate destination.
    978 //
    979 // You shouldn't actually use LogMessage's constructor to log things,
    980 // though.  You should use the LOG() macro (and variants thereof)
    981 // above.
    982 class BASE_EXPORT LogMessage {
    983  public:
    984   // Used for LOG(severity).
    985   LogMessage(const char* file, int line, LogSeverity severity);
    986 
    987   // Used for CHECK().  Implied severity = LOG_FATAL.
    988   LogMessage(const char* file, int line, const char* condition);
    989 
    990   // Used for CHECK_EQ(), etc. Takes ownership of the given string.
    991   // Implied severity = LOG_FATAL.
    992   LogMessage(const char* file, int line, std::string* result);
    993 
    994   // Used for DCHECK_EQ(), etc. Takes ownership of the given string.
    995   LogMessage(const char* file, int line, LogSeverity severity,
    996              std::string* result);
    997 
    998   ~LogMessage();
    999 
   1000   std::ostream& stream() { return stream_; }
   1001 
   1002   LogSeverity severity() { return severity_; }
   1003   std::string str() { return stream_.str(); }
   1004 
   1005  private:
   1006   void Init(const char* file, int line);
   1007 
   1008   LogSeverity severity_;
   1009   std::ostringstream stream_;
   1010   size_t message_start_;  // Offset of the start of the message (past prefix
   1011                           // info).
   1012   // The file and line information passed in to the constructor.
   1013   const char* file_;
   1014   const int line_;
   1015 
   1016 #if defined(OS_WIN)
   1017   // Stores the current value of GetLastError in the constructor and restores
   1018   // it in the destructor by calling SetLastError.
   1019   // This is useful since the LogMessage class uses a lot of Win32 calls
   1020   // that will lose the value of GLE and the code that called the log function
   1021   // will have lost the thread error value when the log call returns.
   1022   class SaveLastError {
   1023    public:
   1024     SaveLastError();
   1025     ~SaveLastError();
   1026 
   1027     unsigned long get_error() const { return last_error_; }
   1028 
   1029    protected:
   1030     unsigned long last_error_;
   1031   };
   1032 
   1033   SaveLastError last_error_;
   1034 #endif
   1035 
   1036   DISALLOW_COPY_AND_ASSIGN(LogMessage);
   1037 };
   1038 
   1039 // This class is used to explicitly ignore values in the conditional
   1040 // logging macros.  This avoids compiler warnings like "value computed
   1041 // is not used" and "statement has no effect".
   1042 class LogMessageVoidify {
   1043  public:
   1044   LogMessageVoidify() = default;
   1045   // This has to be an operator with a precedence lower than << but
   1046   // higher than ?:
   1047   void operator&(std::ostream&) { }
   1048 };
   1049 
   1050 #if defined(OS_WIN)
   1051 typedef unsigned long SystemErrorCode;
   1052 #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
   1053 typedef int SystemErrorCode;
   1054 #endif
   1055 
   1056 // Alias for ::GetLastError() on Windows and errno on POSIX. Avoids having to
   1057 // pull in windows.h just for GetLastError() and DWORD.
   1058 BASE_EXPORT SystemErrorCode GetLastSystemErrorCode();
   1059 BASE_EXPORT std::string SystemErrorCodeToString(SystemErrorCode error_code);
   1060 
   1061 #if defined(OS_WIN)
   1062 // Appends a formatted system message of the GetLastError() type.
   1063 class BASE_EXPORT Win32ErrorLogMessage {
   1064  public:
   1065   Win32ErrorLogMessage(const char* file,
   1066                        int line,
   1067                        LogSeverity severity,
   1068                        SystemErrorCode err);
   1069 
   1070   // Appends the error message before destructing the encapsulated class.
   1071   ~Win32ErrorLogMessage();
   1072 
   1073   std::ostream& stream() { return log_message_.stream(); }
   1074 
   1075  private:
   1076   SystemErrorCode err_;
   1077   LogMessage log_message_;
   1078 
   1079   DISALLOW_COPY_AND_ASSIGN(Win32ErrorLogMessage);
   1080 };
   1081 #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
   1082 // Appends a formatted system message of the errno type
   1083 class BASE_EXPORT ErrnoLogMessage {
   1084  public:
   1085   ErrnoLogMessage(const char* file,
   1086                   int line,
   1087                   LogSeverity severity,
   1088                   SystemErrorCode err);
   1089 
   1090   // Appends the error message before destructing the encapsulated class.
   1091   ~ErrnoLogMessage();
   1092 
   1093   std::ostream& stream() { return log_message_.stream(); }
   1094 
   1095  private:
   1096   SystemErrorCode err_;
   1097   LogMessage log_message_;
   1098 
   1099   DISALLOW_COPY_AND_ASSIGN(ErrnoLogMessage);
   1100 };
   1101 #endif  // OS_WIN
   1102 
   1103 // Closes the log file explicitly if open.
   1104 // NOTE: Since the log file is opened as necessary by the action of logging
   1105 //       statements, there's no guarantee that it will stay closed
   1106 //       after this call.
   1107 BASE_EXPORT void CloseLogFile();
   1108 
   1109 // Async signal safe logging mechanism.
   1110 BASE_EXPORT void RawLog(int level, const char* message);
   1111 
   1112 #define RAW_LOG(level, message) \
   1113   ::logging::RawLog(::logging::LOG_##level, message)
   1114 
   1115 #define RAW_CHECK(condition)                               \
   1116   do {                                                     \
   1117     if (!(condition))                                      \
   1118       ::logging::RawLog(::logging::LOG_FATAL,              \
   1119                         "Check failed: " #condition "\n"); \
   1120   } while (0)
   1121 
   1122 #if defined(OS_WIN)
   1123 // Returns true if logging to file is enabled.
   1124 BASE_EXPORT bool IsLoggingToFileEnabled();
   1125 
   1126 // Returns the default log file path.
   1127 BASE_EXPORT std::wstring GetLogFileFullPath();
   1128 #endif
   1129 
   1130 }  // namespace logging
   1131 
   1132 // Note that "The behavior of a C++ program is undefined if it adds declarations
   1133 // or definitions to namespace std or to a namespace within namespace std unless
   1134 // otherwise specified." --C++11[namespace.std]
   1135 //
   1136 // We've checked that this particular definition has the intended behavior on
   1137 // our implementations, but it's prone to breaking in the future, and please
   1138 // don't imitate this in your own definitions without checking with some
   1139 // standard library experts.
   1140 namespace std {
   1141 // These functions are provided as a convenience for logging, which is where we
   1142 // use streams (it is against Google style to use streams in other places). It
   1143 // is designed to allow you to emit non-ASCII Unicode strings to the log file,
   1144 // which is normally ASCII. It is relatively slow, so try not to use it for
   1145 // common cases. Non-ASCII characters will be converted to UTF-8 by these
   1146 // operators.
   1147 BASE_EXPORT std::ostream& operator<<(std::ostream& out, const wchar_t* wstr);
   1148 inline std::ostream& operator<<(std::ostream& out, const std::wstring& wstr) {
   1149   return out << wstr.c_str();
   1150 }
   1151 }  // namespace std
   1152 
   1153 // The NOTIMPLEMENTED() macro annotates codepaths which have not been
   1154 // implemented yet. If output spam is a serious concern,
   1155 // NOTIMPLEMENTED_LOG_ONCE can be used.
   1156 
   1157 #if defined(COMPILER_GCC)
   1158 // On Linux, with GCC, we can use __PRETTY_FUNCTION__ to get the demangled name
   1159 // of the current function in the NOTIMPLEMENTED message.
   1160 #define NOTIMPLEMENTED_MSG "Not implemented reached in " << __PRETTY_FUNCTION__
   1161 #else
   1162 #define NOTIMPLEMENTED_MSG "NOT IMPLEMENTED"
   1163 #endif
   1164 
   1165 #if defined(OS_ANDROID) && defined(OFFICIAL_BUILD)
   1166 #define NOTIMPLEMENTED() EAT_STREAM_PARAMETERS
   1167 #define NOTIMPLEMENTED_LOG_ONCE() EAT_STREAM_PARAMETERS
   1168 #else
   1169 #define NOTIMPLEMENTED() LOG(ERROR) << NOTIMPLEMENTED_MSG
   1170 #define NOTIMPLEMENTED_LOG_ONCE()                      \
   1171   do {                                                 \
   1172     static bool logged_once = false;                   \
   1173     LOG_IF(ERROR, !logged_once) << NOTIMPLEMENTED_MSG; \
   1174     logged_once = true;                                \
   1175   } while (0);                                         \
   1176   EAT_STREAM_PARAMETERS
   1177 #endif
   1178 
   1179 #endif  // BASE_LOGGING_H_
   1180