Simplify signal handler

Try to use signal-safe functions as much as possible
Closes #3995
Define sys_signame[] ourselves on linux

src/app/main.cpp

@@ -79,10 +79,15 @@ Q_IMPORT_PLUGIN(qico)
 
 // Signal handlers
 #if defined(Q_OS_UNIX) || defined(STACKTRACE_WIN)
-void sigintHandler(int);
-void sigtermHandler(int);
-void sigsegvHandler(int);
-void sigabrtHandler(int);
+void sigNormalHandler(int signum);
+void sigAbnormalHandler(int signum);
+// sys_signame[] is only defined in BSD
+const char *sysSigName[] = {
+    "", "SIGHUP", "SIGINT", "SIGQUIT", "SIGILL", "SIGTRAP", "SIGABRT", "SIGBUS", "SIGFPE", "SIGKILL",
+    "SIGUSR1", "SIGSEGV", "SIGUSR2", "SIGPIPE", "SIGALRM", "SIGTERM", "SIGSTKFLT", "SIGCHLD", "SIGCONT", "SIGSTOP",
+    "SIGTSTP", "SIGTTIN", "SIGTTOU", "SIGURG", "SIGXCPU", "SIGXFSZ", "SIGVTALRM", "SIGPROF", "SIGWINCH", "SIGIO",
+    "SIGPWR", "SIGUNUSED"
+};
 #endif
 
 struct QBtCommandLineParameters
@@ -240,10 +245,10 @@ int main(int argc, char *argv[])
 #endif
 
 #if defined(Q_OS_UNIX) || defined(STACKTRACE_WIN)
-    signal(SIGABRT, sigabrtHandler);
-    signal(SIGTERM, sigtermHandler);
-    signal(SIGINT, sigintHandler);
-    signal(SIGSEGV, sigsegvHandler);
+    signal(SIGINT, sigNormalHandler);
+    signal(SIGTERM, sigNormalHandler);
+    signal(SIGABRT, sigAbnormalHandler);
+    signal(SIGSEGV, sigAbnormalHandler);
 #endif
 
     return app->exec(params.torrents);
@@ -303,58 +308,41 @@ QBtCommandLineParameters parseCommandLine()
 }
 
 #if defined(Q_OS_UNIX) || defined(STACKTRACE_WIN)
-void sigintHandler(int)
+void sigNormalHandler(int signum)
 {
-    signal(SIGINT, 0);
-    qDebug("Catching SIGINT, exiting cleanly");
-    qApp->exit();
-}
-
-void sigtermHandler(int)
-{
-    signal(SIGTERM, 0);
-    qDebug("Catching SIGTERM, exiting cleanly");
-    qApp->exit();
-}
-
-void sigsegvHandler(int)
-{
-    signal(SIGABRT, 0);
-    signal(SIGSEGV, 0);
 #if !defined Q_OS_WIN && !defined Q_OS_HAIKU
-    std::cerr << "\n\n*************************************************************\n";
-    std::cerr << "Catching SIGSEGV, please report a bug at http://bug.qbittorrent.org\nand provide the following backtrace:\n";
-    std::cerr << "qBittorrent version: " << VERSION << std::endl;
-    print_stacktrace();
-#else
-#ifdef STACKTRACE_WIN
-    StraceDlg dlg;
-    dlg.setStacktraceString(straceWin::getBacktrace());
-    dlg.exec();
-#endif
-#endif
-    raise(SIGSEGV);
+    const char str1[] = "Catching signal: ";
+    const char *sigName = sysSigName[signum];
+    const char str2[] = "\nExiting cleanly\n";
+    write(STDERR_FILENO, str1, strlen(str1));
+    write(STDERR_FILENO, sigName, strlen(sigName));
+    write(STDERR_FILENO, str2, strlen(str2));
+#endif // !defined Q_OS_WIN && !defined Q_OS_HAIKU
+    signal(signum, SIG_DFL);
+    qApp->exit();  // unsafe, but exit anyway
 }
 
-void sigabrtHandler(int)
+void sigAbnormalHandler(int signum)
 {
-    signal(SIGABRT, 0);
-    signal(SIGSEGV, 0);
 #if !defined Q_OS_WIN && !defined Q_OS_HAIKU
-    std::cerr << "\n\n*************************************************************\n";
-    std::cerr << "Catching SIGABRT, please report a bug at http://bug.qbittorrent.org\nand provide the following backtrace:\n";
-    std::cerr << "qBittorrent version: " << VERSION << std::endl;
-    print_stacktrace();
-#else
+    const char str1[] = "\n\n*************************************************************\nCatching signal: ";
+    const char *sigName = sysSigName[signum];
+    const char str2[] = "\nPlease file a bug report at http://bug.qbittorrent.org and provide the following information:\n\n"
+    "qBittorrent version: " VERSION "\n";
+    write(STDERR_FILENO, str1, strlen(str1));
+    write(STDERR_FILENO, sigName, strlen(sigName));
+    write(STDERR_FILENO, str2, strlen(str2));
+    print_stacktrace();  // unsafe
+#endif // !defined Q_OS_WIN && !defined Q_OS_HAIKU
 #ifdef STACKTRACE_WIN
-    StraceDlg dlg;
+    StraceDlg dlg;  // unsafe
     dlg.setStacktraceString(straceWin::getBacktrace());
     dlg.exec();
-#endif
-#endif
-    raise(SIGABRT);
+#endif // STACKTRACE_WIN
+    signal(signum, SIG_DFL);
+    raise(signum);
 }
-#endif
+#endif // defined(Q_OS_UNIX) || defined(STACKTRACE_WIN)
 
 #ifndef DISABLE_GUI
 void showSplashScreen()