cnq3/code/linux/linux_signals.cpp

/*
===========================================================================
Copyright (C) 1999-2005 Id Software, Inc.

This file is part of Quake III Arena source code.

Quake III Arena source code is free software; you can redistribute it
and/or modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the License,
or (at your option) any later version.

Quake III Arena source code is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Quake III Arena source code; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
===========================================================================
*/
#include <signal.h>
#include <execinfo.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <dlfcn.h>
#include <cxxabi.h>
#include <sys/stat.h>
#include <sys/types.h>

// empty struct size being 0 or 1 byte
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wextern-c-compat"
#define UNW_LOCAL_ONLY
#include "../libunwind/libunwind.h"
#pragma clang diagnostic pop

#include "../qcommon/q_shared.h"
#include "../qcommon/qcommon.h"
#include "../qcommon/crash.h"
#include "linux_local.h"


/*
A sub-process created by fork from a signal handler will most certainly
run in the context of the signal handler and should therefore also be
limited to calling async-signal-safe functions only.

So the idea of launching a new process from a handler for doing the heavy
lifting (resolving symbols etc) is completely dead.
*/


// the app crashed
// columns: Symbol, Desc
#define CRASH_SIGNAL_LIST(X) \
	X(SIGILL,	"illegal instruction") \
	X(SIGIOT,	"IOT trap (a synonym for SIGABRT)") \
	X(SIGBUS,	"bus error (bad memory access)") \
	X(SIGFPE,	"fatal arithmetic error") \
	X(SIGSEGV,	"invalid memory reference")

// the app should terminate normally
// columns: Symbol, Desc
#define TERM_SIGNAL_LIST(X) \
	X(SIGHUP,	"hangup detected on controlling terminal or death of controlling process") \
	X(SIGQUIT,	"quit from keyboard") \
	X(SIGTRAP,	"trace/breakpoint trap") \
	X(SIGTERM,	"termination signal") \
	X(SIGINT,	"interrupt")


#define SIGNAL_ITEM(Symbol, Desc) 1 + 
static const int sig_crashSignalCount = CRASH_SIGNAL_LIST(SIGNAL_ITEM) 0;
static const int sig_termSignalCount = TERM_SIGNAL_LIST(SIGNAL_ITEM) 0;
#undef SIGNAL_ITEM
	

#define SIGNAL_ITEM(Symbol, Desc) Symbol,
static const int sig_crashSignals[sig_crashSignalCount + 1] = 
{
	CRASH_SIGNAL_LIST(SIGNAL_ITEM)
	0
};
static const int sig_termSignals[sig_termSignalCount + 1] = 
{
	TERM_SIGNAL_LIST(SIGNAL_ITEM)
	0
};
#undef SIGNAL_ITEM


static char sig_backTraceFilePath[MAX_OSPATH];
static char sig_jsonFilePath[MAX_OSPATH];


static void Sig_Unwind_OpenLibrary();
static void Sig_Unwind_GetContext();
static void Sig_Unwind_Print(FILE* file);
static void Sig_Unwind_PrintASS(int fd); // async-signal-safe


// both of these can call Com_Error, which is not safe
#define Q_strncpyz	Sig_strncpyz
#define Q_strcat	Sig_strcat

// make sure we don't use these
#define strcpy		do_not_use_strcpy
#define strcat		do_not_use_strcat


// async-signal-safe
static void Sig_strncpyz(char* dest, const char* src, int size)
{
	if (!dest || !src || size < 1)
		return;

	strncpy(dest, src, size - 1);
	dest[size - 1] = '\0';
}


// async-signal-safe
static void Sig_strcat(char* dest, int size, const char* src)
{
	if (!dest || !src || size < 1)
		return;

	const int destLength = strlen(dest);
	if (destLength >= size)
		return;

	Sig_strncpyz(dest + destLength, src, size - destLength);
}


static const char* Sig_GetDescription(int sig)
{
#define SIGNAL_ITEM(Symbol, Desc) case Symbol: return Desc;
	switch (sig)
	{
		CRASH_SIGNAL_LIST(SIGNAL_ITEM)
		TERM_SIGNAL_LIST(SIGNAL_ITEM)
		default: return "unhandled signal";
	}
#undef SIGNAL_ITEM
}


static const char* Sig_GetName(int sig)
{
#define SIGNAL_ITEM(Symbol, Desc) case Symbol: return #Symbol;
	switch (sig)
	{
		CRASH_SIGNAL_LIST(SIGNAL_ITEM)
		TERM_SIGNAL_LIST(SIGNAL_ITEM)
		default: return "unhandled signal";
	}
#undef SIGNAL_ITEM
}


static void Sig_UpdateFilePaths()
{	
	// gmtime and va (sprintf) are not async-signal-safe

	const time_t epochTime = time(NULL);
	struct tm* const utcTime = gmtime(&epochTime);
	const int y = 1900 + utcTime->tm_year;
	const int m = utcTime->tm_mon + 1;
	const int d = utcTime->tm_mday;
	const int h = utcTime->tm_hour;
	const int mi = utcTime->tm_min;
	const int s = utcTime->tm_sec;

	const char* const bn = va(
		"%s-crash-%d.%02d.%02d-%02d.%02d.%02d",
		q_argv[0], y, m, d, h, mi, s);
	char baseName[MAX_OSPATH];
	Q_strncpyz(baseName, bn, sizeof(baseName));
	Q_strncpyz(sig_backTraceFilePath, va("%s.bt", baseName), sizeof(sig_backTraceFilePath));
	Q_strncpyz(sig_jsonFilePath, va("%s.json", baseName), sizeof(sig_jsonFilePath));
}


static const char* Sig_BackTraceFilePath()
{
	if (sig_backTraceFilePath[0] == '\0')
		return "cnq3-crash.bt";

	return sig_backTraceFilePath;
}


static const char* Sig_JSONFilePath()
{
	if (sig_jsonFilePath[0] == '\0')
		return "cnq3-crash.json";

	return sig_jsonFilePath;
}


static void Sig_WriteJSON(int sig)
{
	FILE* const file = fopen(Sig_JSONFilePath(), "w");
	if (file == NULL)
		return;

	JSONW_BeginFile(file);
	JSONW_IntegerValue("signal", sig);
	JSONW_StringValue("signal_name", Sig_GetName(sig));
	JSONW_StringValue("signal_description", Sig_GetDescription(sig));
	Crash_PrintToFile(q_argv[0]);
	JSONW_EndFile();
	fclose(file);
}


static void Sig_Backtrace_Print(FILE* file)
{
	void* addresses[64];
	const int addresscount = backtrace(addresses, sizeof(addresses));
	if (addresscount > 0)
	{
		fflush(file);
		backtrace_symbols_fd(addresses, addresscount, fileno(file));
	}
	else
	{
		fprintf(file, "The call to backtrace failed\r\n");
	}
}


static void libbt_ErrorCallback(void* data, const char* msg, int errnum)
{
	fprintf((FILE*)data, "libbacktrace error: %s (%d)\r\n", msg, errnum);
}


static void Sig_Print(int fd, const char* msg)
{
	write(fd, msg, strlen(msg));
}


static void Sig_PrintLine(int fd, const char* msg)
{
	write(fd, msg, strlen(msg));
	write(fd, "\r\n", 2);
}


static void Sig_PrintSignalCaught(int sig)
{	
	// fprintf is not async-signal-safe, but write is
	Sig_Print(STDERR_FILENO, "\nSignal caught: ");
	Sig_Print(STDERR_FILENO, Sig_GetName(sig));
	Sig_Print(STDERR_FILENO, " (");
	Sig_Print(STDERR_FILENO, Sig_GetDescription(sig));
	Sig_Print(STDERR_FILENO, ")\r\n");
}


static void Sig_HandleExit()
{
	Lin_ConsoleInputShutdown();
}


static volatile sig_atomic_t sig_termRequested = 0;


static void Sig_HandleTermSignal(int sig)
{
	Sig_PrintSignalCaught(sig);
	sig_termRequested = 1;
}


static void Sig_PrintAttempt(const char* what)
{
	Sig_Print(STDERR_FILENO, "Attempting to ");
	Sig_Print(STDERR_FILENO, what);
	Sig_Print(STDERR_FILENO, "...");
}


static void Sig_PrintDone()
{
	Sig_Print(STDERR_FILENO, " done\r\n");
}


static void Sig_HandleCrash(int sig)
{
	//
	// Phase 1: async-signal-safe code
	//

	Sig_Unwind_GetContext();

	const int fd = open(Sig_BackTraceFilePath(), O_CREAT | O_TRUNC | O_WRONLY, 0644);
	if (fd != -1)
	{
		Sig_PrintAttempt("write safe libunwind stack trace");
		Sig_PrintLine(fd, "safe libunwind stack trace:");
		Sig_Unwind_PrintASS(fd);
		Sig_PrintDone();

		Sig_PrintAttempt("write safe mod stack traces");
		Sig_PrintLine(fd, "\r\n\r\nmod stack traces:");
		Crash_PrintVMStackTracesASS(fd);
		Sig_PrintDone();

		// user R+W - group R - others R
		chmod(Sig_BackTraceFilePath(), S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
	}

	//
	// Phase 2: buckle up
	//

	Sig_PrintAttempt("restore tty settings");
	Lin_ConsoleInputShutdown();
	Sig_PrintDone();

	Sig_PrintAttempt("write JSON report");
	Sig_WriteJSON(sig);
	Sig_PrintDone();

	if (fd != -1)
	{
		FILE* const file = fdopen(fd, "a");

		Sig_PrintAttempt("write backtrace stack trace");
		fprintf(file, "\r\n\r\nbacktrace_symbols_fd stack trace:\r\n");
		Sig_Backtrace_Print(file);
		fflush(file);
		Sig_PrintDone();

		Sig_PrintAttempt("write detailed libunwind stack trace");
		fprintf(file, "\r\n\r\ndetailed libunwind stack trace:\r\n");
		Sig_Unwind_Print(file);
		fflush(file);
		Sig_PrintDone();
	}
}


static void Sig_HandleCrashSignal(int sig)
{
	static volatile sig_atomic_t counter = 0;

	Sig_PrintSignalCaught(sig);

	++counter;

	if (counter == 1)
		Sig_HandleCrash(sig);
	else if (counter >= 2)
		Sig_PrintLine(STDERR_FILENO, "Double fault! Shutting down immediately.");

	_exit(1);
}


static void Sig_RegisterSignals(const int* signals, int count, void (*handler)(int), int flags)
{
	sigset_t mask;
	sigemptyset(&mask);
	
	struct sigaction action;
	memset(&action, 0, sizeof(action));
	action.sa_handler = handler;
	action.sa_mask = mask;
	action.sa_flags = flags;
	for (int i = 0; i < count; ++i)
		sigaction(signals[i], &action, NULL);
}


void SIG_InitChild()
{	
	// This is unfortunately needed because some code might
	// call exit and bypass all the clean-up work without
	// there ever being a real crash.
	// This happens for instance with the "fatal IO error"
	// of the X server.
	atexit(Sig_HandleExit);

	// The crash handler gets SA_NODEFER so that we can handle faults it generates.
	Sig_RegisterSignals(sig_crashSignals, sig_crashSignalCount, Sig_HandleCrashSignal, SA_NODEFER);
	Sig_RegisterSignals(sig_termSignals, sig_termSignalCount, Sig_HandleTermSignal, 0);

	// Must do this now because it's not safe in a signal handler.
	Sig_UpdateFilePaths();
	Sig_Unwind_OpenLibrary();
}


void SIG_InitParent()
{
	// Signals are sent to both the parent and the child, which can be an issue.
	// Our parent process has to ignore all signals handled by the child and
	// let the child do whatever needs to be done.

	for (int i = 0; i < sig_crashSignalCount; ++i)
		signal(sig_crashSignals[i], SIG_IGN);

	for (int i = 0; i < sig_termSignalCount; ++i)
		signal(sig_termSignals[i], SIG_IGN);
}


void SIG_Frame()
{
	// Must do this now because it's not safe in a signal handler.
	Sig_UpdateFilePaths();

	if (sig_termRequested != 0)
		Com_Quit(0);
}


// We require libunwind8 specifically for now.
// Even if there was a general symlink without the number,
// it would still not be safe to load it because
// the library provides no way to query its version.
#define LIBUNWIND_PATH "libunwind-" XSTRING(UNW_TARGET) ".so.8"


struct libUnwind_t
{
	unw_context_t context;
	int (*getcontext)(unw_context_t *);
	int (*init_local)(unw_cursor_t *, unw_context_t *);
	int (*step)(unw_cursor_t *);
	int (*get_reg)(unw_cursor_t *, unw_regnum_t, unw_word_t *);
	int (*get_proc_name)(unw_cursor_t *, char *, size_t, unw_word_t *);
	void* handle;
	qbool valid;
};


static libUnwind_t unw;


static void Sig_Unwind_GetContext()
{
	if (!unw.valid)
		return;

	if (unw.getcontext(&unw.context) != 0)
	{
		Sig_PrintLine(STDERR_FILENO, "The call to libunwind's getcontext failed");
		unw.valid = qfalse;
	}
}


static int Sig_Unwind_GetFunction(void** func, const char* name)
{
	*func = dlsym(unw.handle, name);

	return *func != NULL;
}


static void Sig_Unwind_OpenLibrary()
{
	// dlopen, dlsym, fprintf are not async-signal-safe

	unw.valid = qfalse;
	unw.handle = dlopen(LIBUNWIND_PATH, RTLD_NOW);
	if (unw.handle == NULL)
	{
		const char* errorMsg = dlerror();
		if (errorMsg != NULL)
			fprintf(stderr, "\nFailed to load %s: %s\n", LIBUNWIND_PATH, errorMsg);
		else
			fprintf(stderr, "\nFailed to find/load %s\n", LIBUNWIND_PATH);
		return;	
	}

#define GET2(Var, Name) \
	if (!Sig_Unwind_GetFunction((void**)&unw.Var, Name)) \
	{ \
		fprintf(stderr, "\nFailed to find libunwind function %s\n", Name); \
		return; \
	}
#define GET(Name) GET2(Name, XSTRING(UNW_OBJ(Name)))
	GET2(getcontext, "_Ux86_64_getcontext");
	GET(init_local);
	GET(step);
	GET(get_reg);
	GET(get_proc_name);
#undef GET
#undef GET2

	unw.valid = qtrue;
}


static int Sig_Unwind_GetFileAndLine(unw_word_t addr, char* file, size_t flen, int* line)
{
	static char buf[1024];

	sprintf(buf, "addr2line -C -e %s -f -i %lx", q_argv[0], (unsigned long)addr);
	FILE* f = popen(buf, "r");
	if (f == NULL)
		return 0;

	fgets(buf, sizeof(buf), f); // function name
	fgets(buf, sizeof(buf), f); // file and line
	pclose(f);

	if (buf[0] == '?')
		return 0;

	// file name before ':'
	char* p = buf;
	while (*p != ':')
		++p;
	*p = '\0';

	// skip the folder names
	char* name = strrchr(buf, '/');
	name = name ? (name + 1) : buf;

	// line number
	++p;
	Q_strncpyz(file, name, flen);
	sscanf(p, "%d", line);

	return 1;
}


void Sig_Unwind_Print(FILE* fp)
{
	static char name[1024];
	static char file[1024];
	
	if (!unw.valid)
		return;

	unw_cursor_t cursor;
	if (unw.init_local(&cursor, &unw.context) != 0)
	{
		fprintf(fp, "The call to libunwind's init_local failed\r\n");
		return;
	}

	while (unw.step(&cursor) > 0)
	{
		const char* func = name;
		unw_word_t ip, sp, offp;
		if (unw.get_proc_name(&cursor, name, sizeof(name), &offp))
		{
			Q_strncpyz(name, "???", sizeof(name));
		}
		else
		{
			int status;
			char* niceName = abi::__cxa_demangle(name, NULL, NULL, &status);
			if (status == 0)
			{
				Q_strncpyz(name, niceName, sizeof(name));
				free(niceName);
			}
		}

		int line = 0;
		unw.get_reg(&cursor, UNW_REG_IP, &ip);
		if (Sig_Unwind_GetFileAndLine((long)ip, file, sizeof(file), &line))
			fprintf(fp, "%s at %s:%d\n", name, file, line);
		else
			fprintf(fp, "%s\n", name);
	}
}


// async-signal-safe
void Sig_Unwind_PrintASS(int fd)
{
	static char name[1024];

	if (!unw.valid)
		return;

	unw_cursor_t cursor;
	if (unw.init_local(&cursor, &unw.context) != 0)
		return;

	while (unw.step(&cursor) > 0)
	{
		unw_word_t offp;
		if (unw.get_proc_name(&cursor, name, sizeof(name), &offp))
			Q_strncpyz(name, "???", sizeof(name));

		Sig_PrintLine(fd, name);
	}
}