nix: Fork before game code and wait to catch signals and coredumps

Ditched signal_handler to avoid worrying about async-signal-safe functions.
D_QuitNetGame is not called, so players whose programs are interrupted by a
signal will time out from the server. Because the game runs in a child process,
the window can close before the "Signal Caught" text box appears.

"(core dumped)" is also included in the message if core dumping could be
determined.

src/doomdef.h

@@ -125,6 +125,10 @@
 #define LOGMESSAGES // write message in log.txt
 #endif
 
+#if (defined (__unix__) && !defined (_MSDOS)) || defined (UNIXCOMMON)
+#define NEWSIGNALHANDLER
+#endif
+
 #ifdef LOGMESSAGES
 extern FILE *logstream;
 #endif

src/i_system.h

@@ -84,6 +84,10 @@ ticcmd_t *I_BaseTiccmd2(void);
 */
 void I_Quit(void) FUNCNORETURN;
 
+/**	\brief Print a message and text box about a signal that was raised.
+*/
+void I_ReportSignal(int num, int coredumped);
+
 typedef enum
 {
 	EvilForce = -1,

src/sdl/i_main.c

@@ -28,6 +28,11 @@
 
 #include "time.h" // For log timestamps
 
+#ifdef NEWSIGNALHANDLER
+#include <errno.h>
+#include <sys/wait.h>
+#endif
+
 #ifdef HAVE_SDL
 
 #ifdef HAVE_TTF
@@ -181,6 +186,53 @@ int main(int argc, char **argv)
 #endif
 	MakeCodeWritable();
 #endif
+
+#ifdef NEWSIGNALHANDLER
+	switch (fork())
+	{
+		case -1:
+			I_Error(
+					"Error setting up signal reporting: fork(): %s\n",
+					strerror(errno)
+			);
+			break;
+		case 0:
+			break;
+		default:
+			{
+				int status;
+				int signum;
+				if (wait(&status) == -1)
+				{
+					I_Error(
+							"Error setting up signal reporting: fork(): %s\n",
+							strerror(errno)
+					);
+				}
+				else
+				{
+					if (WIFSIGNALED (status))
+					{
+						signum = WTERMSIG (status);
+#ifdef WCOREDUMP
+						I_ReportSignal(signum, WCOREDUMP (status));
+#else
+						I_ReportSignal(signum, 0);
+#endif
+						status = 128 + signum;
+					}
+					else if (WIFEXITED (status))
+					{
+						status = WEXITSTATUS (status);
+					}
+
+					I_ShutdownSystem();
+					exit(status);
+				}
+			}
+	}
+#endif/*NEWSIGNALHANDLER*/
+
 	// startup SRB2
 	CONS_Printf("Setting up SRB2...\n");
 	D_SRB2Main();

src/sdl/i_system.c

@@ -229,13 +229,11 @@ SDL_bool framebuffer = SDL_FALSE;
 
 UINT8 keyboard_started = false;
 
-FUNCNORETURN static ATTRNORETURN void signal_handler(INT32 num)
+void I_ReportSignal(int num, int coredumped)
 {
 	//static char msg[] = "oh no! back to reality!\r\n";
 	const char *      sigmsg;
-	char        sigdef[32];
-
-	D_QuitNetGame(); // Fix server freezes
+	char msg[128];
 
 	switch (num)
 	{
@@ -261,8 +259,21 @@ FUNCNORETURN static ATTRNORETURN void signal_handler(INT32 num)
 		sigmsg = "SIGABRT - abnormal termination triggered by abort call";
 		break;
 	default:
-		sprintf(sigdef,"signal number %d", num);
-		sigmsg = sigdef;
+		sprintf(msg,"signal number %d", num);
+		if (coredumped)
+			sigmsg = 0;
+		else
+			sigmsg = msg;
+	}
+
+	if (coredumped)
+	{
+		if (sigmsg)
+			sprintf(msg, "%s (core dumped)", sigmsg);
+		else
+			strcat(msg, " (core dumped)");
+
+		sigmsg = msg;
 	}
 
 	I_OutputMsg("\nsignal_handler() error: %s\n", sigmsg);
@@ -270,11 +281,19 @@ FUNCNORETURN static ATTRNORETURN void signal_handler(INT32 num)
 	SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR,
 		"Signal caught",
 		sigmsg, NULL);
+}
+
+#ifndef NEWSIGNALHANDLER
+FUNCNORETURN static ATTRNORETURN void signal_handler(INT32 num)
+{
+	D_QuitNetGame(); // Fix server freezes
+	I_ReportSignal(num, 0);
 	I_ShutdownSystem();
 	signal(num, SIG_DFL);               //default signal action
 	raise(num);
 	I_Quit();
 }
+#endif
 
 FUNCNORETURN static ATTRNORETURN void quit_handler(int num)
 {
@@ -664,10 +683,12 @@ void I_StartupKeyboard (void)
 
 	// If these defines don't exist,
 	// then compilation would have failed above us...
+#ifndef NEWSIGNALHANDLER
 	signal(SIGILL , signal_handler);
 	signal(SIGSEGV , signal_handler);
 	signal(SIGABRT , signal_handler);
 	signal(SIGFPE , signal_handler);
+#endif
 }
 
 //