easylogging++的那些事(四)原始碼分析(八)崩潰處理相關
阿新 • • 發佈：2022-12-07
目錄
在上一篇我們分析了 效能跟蹤 的實現，今天我們來看看崩潰處理相關的一些內容。
在 easylogging++的 功能介紹 中我們簡要介紹過崩潰處理相關的內容。
easylogging++中崩潰處理相關的主要有兩塊: 1) 系統訊號處理器 2) 堆疊跟蹤( 僅僅支援 GCC )
系統訊號處理器
easylogging++支援的訊號如下:
1)SIGABRT訊號 (啟用ELPP_HANDLE_SIGABRT巨集)
2)SIGFPE訊號
3)SIGILL訊號
4)SIGSEGV訊號
5)SIGINT訊號系統訊號處理器的設定主要是通過
CrashHandler類來實現的：
CrashHandler類的實現如下：#if defined(ELPP_FEATURE_ALL) || defined(ELPP_FEATURE_CRASH_LOG) class CrashHandler : base::NoCopy { public: typedef void (*Handler)(int); explicit CrashHandler(bool useDefault); explicit CrashHandler(const Handler &cHandler) { setHandler(cHandler); } void setHandler(const Handler &cHandler); private: Handler m_handler; }; #else class CrashHandler { public: explicit CrashHandler(bool) {} }; #endif // defined(ELPP_FEATURE_ALL) || defined(ELPP_FEATURE_CRASH_LOG)未啟用崩潰處理(未定義
ELPP_FEATURE_ALL巨集或者ELPP_FEATURE_CRASH_LOG巨集)的情況這個類什麼也沒幹。
啟用啟用崩潰處理的情況:setHandler 介面
// 迴圈設定訊號處理器 void CrashHandler::setHandler(const Handler &cHandler) { m_handler = cHandler; #if defined(ELPP_HANDLE_SIGABRT) int i = 0; // SIGABRT is at base::consts::kCrashSignals[0] #else int i = 1; #endif // defined(ELPP_HANDLE_SIGABRT) for (; i < base::consts::kCrashSignalsCount; ++i) { m_handler = signal(base::consts::kCrashSignals[i].numb, cHandler); } }
base::consts::kCrashSignals的定義如下:const struct { int numb; const char *name; const char *brief; const char *detail; } kCrashSignals[] = { // NOTE: Do not re-order, if you do please check CrashHandler(bool) constructor and CrashHandler::setHandler(..) {SIGABRT, "SIGABRT", "Abnormal termination", "Program was abnormally terminated."}, {SIGFPE, "SIGFPE", "Erroneous arithmetic operation", "Arithmetic operation issue such as division by zero or operation resulting in overflow."}, {SIGILL, "SIGILL", "Illegal instruction", "Generally due to a corruption in the code or to an attempt to execute data."}, {SIGSEGV, "SIGSEGV", "Invalid access to memory", "Program is trying to read an invalid (unallocated, deleted or corrupted) or inaccessible memory."}, {SIGINT, "SIGINT", "Interactive attention signal", "Interruption generated (generally) by user or operating system."}, }; static const int kCrashSignalsCount = sizeof(kCrashSignals) / sizeof(kCrashSignals[0]);建構函式
CrashHandler::CrashHandler(bool useDefault) { if (useDefault) { setHandler(defaultCrashHandler); } }
setHandler介面在前面已經介紹過了，這裡就不多說了。
defaultCrashHandler的定義如下:// 預設的訊號處理器 static inline void defaultCrashHandler(int sig) { // 輸出堆疊和崩潰資訊 base::debug::logCrashReason(sig, true, Level::Fatal, base::consts::kDefaultLoggerId); // 終止程式的執行 base::debug::crashAbort(sig); }base:: debug:: logCrashReason 的定義如下:
// 輸出堆疊和崩潰資訊 /// @brief Logs reason of crash from sig static void logCrashReason(int sig, bool stackTraceIfAvailable, Level level, const char *logger) { if (sig == SIGINT && ELPP->hasFlag(el::LoggingFlag::IgnoreSigInt)) { return; } std::stringstream ss; ss << "CRASH HANDLED; "; // 返回指定崩潰訊號的詳細資訊 ss << crashReason(sig); #if ELPP_STACKTRACE // 輸出堆疊資訊 if (stackTraceIfAvailable) { ss << std::endl << " ======= Backtrace: =========" << std::endl << base::debug::StackTrace(); } #else ELPP_UNUSED(stackTraceIfAvailable); #endif // ELPP_STACKTRACE ELPP_WRITE_LOG(el::base::Writer, level, base::DispatchAction::NormalLog, logger) << ss.str(); }
base::debug::crashAbort的定義如下:static inline void crashAbort(int sig) { // 終止程式的執行 base::utils::abort(sig, std::string()); }
crashReason的定義如下:// 返回指定崩潰訊號的詳細資訊 static std::string crashReason(int sig) { std::stringstream ss; bool foundReason = false; for (int i = 0; i < base::consts::kCrashSignalsCount; ++i) { if (base::consts::kCrashSignals[i].numb == sig) { ss << "Application has crashed due to [" << base::consts::kCrashSignals[i].name << "] signal"; if (ELPP->hasFlag(el::LoggingFlag::LogDetailedCrashReason)) { ss << std::endl << " " << base::consts::kCrashSignals[i].brief << std::endl << " " << base::consts::kCrashSignals[i].detail; } foundReason = true; } } if (!foundReason) { ss << "Application has crashed due to unknown signal [" << sig << "]"; } return ss.str(); }上面的這些介面的實現不復雜，這裡就不多說了。
堆疊資訊跟蹤
堆疊資訊跟蹤是通過
StackTrace類實現的。
StackTrace類的實現如下：class StackTrace : base::NoCopy { public: static const unsigned int kMaxStack = 64; // 堆疊的最多條數 static const unsigned int kStackStart = 2; // 堆疊的起始統計位置 We want to skip c'tor and StackTrace::generateNew() // 堆疊的每一條 class StackTraceEntry { public: StackTraceEntry(std::size_t index, const std::string &loc, const std::string &demang, const std::string &hex, const std::string &addr); StackTraceEntry(std::size_t index, const std::string &loc) : m_index(index), m_location(loc) { } std::size_t m_index; std::string m_location; std::string m_demangled; std::string m_hex; std::string m_addr; friend std::ostream &operator<<(std::ostream &ss, const StackTraceEntry &si); private: StackTraceEntry(void); }; StackTrace(void) { generateNew(); } virtual ~StackTrace(void) { } inline std::vector<StackTraceEntry> &getLatestStack(void) { return m_stack; } friend std::ostream &operator<<(std::ostream &os, const StackTrace &st); private: std::vector<StackTraceEntry> m_stack; // 存放堆疊資訊 // 構建堆疊資訊 void generateNew(void); }; StackTrace::StackTraceEntry::StackTraceEntry(std::size_t index, const std::string &loc, const std::string &demang, const std::string &hex, const std::string &addr) : m_index(index), m_location(loc), m_demangled(demang), m_hex(hex), m_addr(addr) { } // 輸出運算子用於支援StackTraceEntry類進行日誌輸出 std::ostream &operator<<(std::ostream &ss, const StackTrace::StackTraceEntry &si) { ss << "[" << si.m_index << "] " << si.m_location << (si.m_hex.empty() ? "" : "+") << si.m_hex << " " << si.m_addr << (si.m_demangled.empty() ? "" : ":") << si.m_demangled; return ss; } // 輸出運算子用於支援StackTrace類進行日誌輸出 std::ostream &operator<<(std::ostream &os, const StackTrace &st) { std::vector<StackTrace::StackTraceEntry>::const_iterator it = st.m_stack.begin(); while (it != st.m_stack.end()) { os << " " << *it++ << "\n"; } return os; }生成堆疊資訊
void StackTrace::generateNew(void) { // glibc標頭檔案"execinfo.h"定義了HAVE_EXECINFO巨集以及堆疊相關的介面backtrace和backtrace_symbols #ifdef HAVE_EXECINFO m_stack.clear(); void *stack[kMaxStack]; // backtrace獲取當前執行緒的呼叫堆疊,獲取的資訊將會被存放在stack中,返回堆疊的總條數 unsigned int size = backtrace(stack, kMaxStack); // backtrace_symbols將從backtrace函式獲取的資訊stack轉化為一個字串陣列. // backtrace_symbols函式返回值strings是一個指向字串陣列的指標,它的大小同stack相同.每個字串包含了一個相對於stack中對應元素的可列印資訊.它包括函式名，函式的偏移地址,和實際的返回地址 char **strings = backtrace_symbols(stack, size); if (size > kStackStart) { // Skip StackTrace c'tor and generateNew // 依次遍歷從kStackStart索引處開始的每條堆疊資訊 for (std::size_t i = kStackStart; i < size; ++i) { std::string mangName; std::string location; std::string hex; std::string addr; // entry: 2 crash.cpp.bin 0x0000000101552be5 _ZN2el4base5debug10StackTraceC1Ev + 21 const std::string line(strings[i]); auto p = line.find("_"); if (p != std::string::npos) { mangName = line.substr(p); mangName = mangName.substr(0, mangName.find(" +")); } p = line.find("0x"); if (p != std::string::npos) { addr = line.substr(p); addr = addr.substr(0, addr.find("_")); } // 函式名的處理 // Perform demangling if parsed properly if (!mangName.empty()) { int status = 0; // abi::__cxa_demangle介面在http://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.3/a01696.html 有詳細介紹 char *demangName = abi::__cxa_demangle(mangName.data(), 0, 0, &status); // if demangling is successful, output the demangled function name if (status == 0) { // Success StackTraceEntry entry(i - 1, location, demangName, hex, addr); m_stack.push_back(entry); } else { // Not successful - we will use mangled name StackTraceEntry entry(i - 1, location, mangName, hex, addr); m_stack.push_back(entry); } free(demangName); } else { StackTraceEntry entry(i - 1, line); m_stack.push_back(entry); } } } free(strings); #else ELPP_INTERNAL_INFO(1, "Stacktrace generation not supported for selected compiler"); #endif // ELPP_STACKTRACE }
generateNew都是對底層一些堆疊資訊介面的呼叫得到的資訊逐步進行解析，這塊我研究的不多，就不做過多解釋了。感興趣的可以參考相關文件進行進一步的瞭解。
對外提供的介面
對外提供的設定介面主要是有
el::Helpers實現的:static inline void setCrashHandler(const el::base::debug::CrashHandler::Handler &crashHandler) { el::elCrashHandler.setHandler(crashHandler); } void Helpers::crashAbort(int sig, const char *sourceFile, unsigned int long line) { std::stringstream ss; ss << base::debug::crashReason(sig).c_str(); ss << " - [Called el::Helpers::crashAbort(" << sig << ")]"; if (sourceFile != nullptr && strlen(sourceFile) > 0) { ss << " - Source: " << sourceFile; if (line > 0) ss << ":" << line; else ss << " (line number not specified)"; } base::utils::abort(sig, ss.str()); } void Helpers::logCrashReason(int sig, bool stackTraceIfAvailable, Level level, const char *logger) { el::base::debug::logCrashReason(sig, stackTraceIfAvailable, level, logger); }上面的這些介面的實現不復雜，這裡就不多說了。
至此，崩潰處理相關的內容就介紹完了，下一篇我們開始介紹非同步日誌的實現。