crash handler on linux

Author: malytomas

sources/libcore/crashHandlerLinux.cpp

@@ -0,0 +1,149 @@
+#ifdef CAGE_SYSTEM_LINUX
+
+	#include <csignal>
+	#include <cstddef>
+	#include <cstdio>
+	#include <cstdlib>
+	#include <cstring>
+	#include <cerrno>
+	#include <execinfo.h>
+	#include <sys/mman.h>
+	#include <ucontext.h>
+	#include <unistd.h>
+
+	#include <cage-core/core.h>
+
+namespace cage
+{
+	int crashHandlerLogFileFd = STDERR_FILENO;
+
+	namespace
+	{
+		void *altStackMem = nullptr;
+		constexpr int OldHandlersCount = 16;
+		struct sigaction prevHandlers[OldHandlersCount] = {};
+
+		struct sigaction *prevHandler(int sig)
+		{
+			if (sig >= 0 && sig < OldHandlersCount)
+				return &prevHandlers[sig];
+			return nullptr;
+		}
+
+		const char *sigToStr(int sig)
+		{
+			switch (sig)
+			{
+				case SIGSEGV:
+					return "SIGSEGV";
+				case SIGABRT:
+					return "SIGABRT";
+				case SIGFPE:
+					return "SIGFPE";
+				case SIGILL:
+					return "SIGILL";
+				case SIGBUS:
+					return "SIGBUS";
+				case SIGTRAP:
+					return "SIGTRAP";
+				case SIGTERM:
+					return "SIGTERM";
+				default:
+					return "UNKNOWN";
+			}
+		}
+
+		void safeWrite(const String &s)
+		{
+			write(crashHandlerLogFileFd, s.c_str(), s.length());
+		}
+
+		void printStackTrace()
+		{
+			// backtrace (best-effort; not strictly async-signal-safe)
+			static constexpr int kMaxFrames = 256;
+			void *frames[kMaxFrames];
+			int n = backtrace(frames, kMaxFrames);
+			safeWrite(Stringizer() + "stack trace:\n");
+			backtrace_symbols_fd(frames, n, crashHandlerLogFileFd); // writes directly to fd
+		}
+
+		void crashHandler(int sig, siginfo_t *si, void *uctx)
+		{
+			safeWrite(Stringizer() + "signal caught: " + sigToStr(sig) + " (" + sig + ")\n");
+
+			if (si)
+				safeWrite(Stringizer() + "fault addr: " + (uintptr_t)si->si_addr + ", code: " + si->si_code + "\n");
+
+			printStackTrace();
+
+			if (struct sigaction *prev = prevHandler(sig))
+			{
+				if (prev->sa_flags & SA_SIGINFO)
+				{
+					// previous handler expects 3 arguments
+					prev->sa_sigaction(sig, si, uctx);
+				}
+				else if (prev->sa_handler == SIG_DFL || prev->sa_handler == SIG_IGN)
+				{
+					// default or ignore: you can reset signal to default and raise
+					signal(sig, prev->sa_handler);
+					raise(sig);
+				}
+				else
+				{
+					// simple handler with 1 argument
+					prev->sa_handler(sig);
+				}
+			}
+
+			// re-raise to trigger default handler (and core dump, if enabled)
+			signal(sig, SIG_DFL);
+			raise(sig);
+		}
+
+		void installAltStack()
+		{
+			static constexpr size_t kAltStackSz = 128 * 1024; // bigger than SIGSTKSZ for safety
+			altStackMem = mmap(nullptr, kAltStackSz, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+			if (altStackMem == MAP_FAILED)
+				altStackMem = std::malloc(kAltStackSz); // fallback to malloc
+			stack_t ss{};
+			ss.ss_sp = altStackMem;
+			ss.ss_size = kAltStackSz;
+			ss.ss_flags = 0;
+			if (sigaltstack(&ss, nullptr) != 0)
+			{
+				CAGE_LOG(SeverityEnum::Info, "crash-handler", strerror(errno));
+				CAGE_THROW_ERROR(Exception, "sigaltstack")
+			}
+		}
+
+		void installHandler(int sig)
+		{
+			struct sigaction sa
+			{};
+			sa.sa_sigaction = &crashHandler;
+			sigemptyset(&sa.sa_mask);
+			sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
+			if (sigaction(sig, &sa, prevHandler(sig)) != 0)
+			{
+				CAGE_LOG(SeverityEnum::Info, "crash-handler", strerror(errno));
+				CAGE_THROW_ERROR(Exception, "sigaction")
+			}
+		}
+
+		struct SetupHandlers
+		{
+			SetupHandlers()
+			{
+				installAltStack();
+				int signals[] = { SIGSEGV, SIGABRT, SIGFPE, SIGILL, SIGBUS, SIGTRAP };
+				for (int s : signals)
+					installHandler(s);
+			}
+		} setupHandlers;
+	}
+}
+
+#endif // CAGE_SYSTEM_LINUX

sources/libcore/crashHandler.cpp renamed to sources/libcore/crashHandlerWindows.cpp

@@ -1,7 +1,9 @@
 #ifdef CAGE_SYSTEM_WINDOWS
+
 	#include <mutex>
 	#include "windowsMinimumInclude.h"
 	#include <DbgHelp.h>
+
 	#pragma comment(lib, "DbgHelp.lib")
 	#define EXCEPTION_CPP 0xE06D7363
 	#define EXCEPTION_DOTNET 0xE0434352

sources/libcore/filesystem/realFiles.cpp

@@ -794,4 +794,12 @@ namespace cage
 #endif
 		}
 	}
+
+#ifdef CAGE_SYSTEM_LINUX
+	int realFileGetFd(File *f)
+	{
+		FileRealBase *base = class_cast<FileRealBase *>(f);
+		return fileno(base->f);
+	}
+#endif
 }

sources/libcore/logger.cpp

@@ -20,6 +20,11 @@
 
 namespace cage
 {
+#ifdef CAGE_SYSTEM_LINUX
+	extern int crashHandlerLogFileFd;
+	int realFileGetFd(File *f);
+#endif
+
 	Holder<File> realNewFile(const String &path, const FileMode &mode);
 	void realTryFlushFile(File *f);
 
@@ -305,7 +310,12 @@ namespace cage
 				fm.textual = true;
 				fm.append = append;
 				if (realFilesystemOnly)
+				{
 					f = realNewFile(path, fm);
+#ifdef CAGE_SYSTEM_LINUX
+					crashHandlerLogFileFd = realFileGetFd(+f);
+#endif
+				}
 				else
 					f = newFile(path, fm);
 			}