Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!husc6!cmcl2!brl-adm!umd5!decuac!felix!chuck
From: chuck@felix.UUCP
Newsgroups: comp.unix.ultrix
Subject: Re: Ultrix 2.0 executable dumps core on 1.2
Message-ID: <13284@felix.UUCP>
Date: Wed, 18-Nov-87 12:04:36 EST
Article-I.D.: felix.13284
Posted: Wed Nov 18 12:04:36 1987
Date-Received: Sat, 21-Nov-87 06:32:59 EST
References: <12683@felix.UUCP>
Sender: chuck@felix.UUCP
Reply-To: gwyn@brl-smoke.arpa (Doug Gwyn )
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 61
Approved: zemon@felix.UUCP

Reply-Path:


In article <12683@felix.UUCP> mark@applix.UUCP (Mark Fox) writes:
>2) Will subsequent versions of Ultrix simply return an error to a
>   "Bad system call" or will they continue to rudely and inexcusably dump
>   core? Really, dumping core is a bug not a feature, isn't it?

Ahem -- I suspect that a SIGSYS was generated, and since you didn't
establish a signal handler for it, you got the default action, which
is "abnormal termination with actions" (in POSIX parlance).  An example
of how to recover from unsupported system calls, extracted from my
getdents() system call emulation for "random UNIX variants", follows;
it can be adapted to deal with other cases where there is a C library
system call hook but where it is not certain that the target system's
kernel will support the system call:

#include	<signal.h>

extern int	_getdents();		/* actual system call */

static enum	{ maybe, no, yes }	state = maybe;
					/* does _getdents() work? */

/*ARGSUSED*/
static void
sig_catch( sig )
	int	sig;			/* must be SIGSYS */
	{
	state = no;			/* attempted _getdents() faulted */
	}

int
getdents( fildes, buf, nbyte )		/* returns # bytes read;
					   0 on EOF, -1 on error */
	int			fildes;	/* directory file descriptor */
	char			*buf;	/* where to put the (struct dirent)s */
	unsigned		nbyte;	/* size of buf[] */
	{
...
	switch ( state )
		{
		void		(*shdlr)();	/* entry SIGSYS handler */
		register int	retval;	/* return from _getdents() if any */

	case yes:			/* _getdents() is known to work */
		return _getdents( fildes, buf, nbyte );

	case maybe:			/* first time only */
		shdlr = signal( SIGSYS, sig_catch );
		retval = _getdents( fildes, buf, nbyte );	/* try it */
		(void)signal( SIGSYS, shdlr );

		if ( state == maybe )	/* SIGSYS did not occur */
			{
			state = yes;	/* so _getdents() must have worked */
			return retval;
			}
		/* else fall through into emulation */

/*	case no:	/* fall through into emulation */
		}
...