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From: net@tub.UUCP (Oliver Laumann)
Newsgroups: comp.sys.hp
Subject: Re: alloca() on the HP9000/300
Message-ID: <1464@tub.UUCP>
Date: 16 Aug 90 17:59:43 GMT
References: <1455@tub.UUCP> <1340135@hpclscu.HP.COM> <1990Aug15.101314.9626@hellgate.utah.edu>
Reply-To: net@tub.UUCP (Oliver Laumann)
Organization: Technical University of Berlin, Germany
Lines: 34

In article <1990Aug15.101314.9626@hellgate.utah.edu> moore%cdr.utah.edu@cs.utah.edu (Tim Moore) writes:

> There are all sorts of reasons why alloca is nice; the luxury of not
> having to call free () is only one of them. Another feature is
> automatic deallocation of storage on catching a signal or a longjmp.

Yes, there are more uses for alloca() than you may dream of in your
worst alloca-nightmares.  One of the reasons why the application that
I have ported to the HP9000 needs alloca() is that it must adjust the
stack pointer on entry to main().  The program starts like this:

    main (ac, av) char **av; {
	char foo;
	if (Was_Dumped) {
	    (void)alloca (INITIAL_STK_OFFSET - (original_stkbase - &foo));
	} else {
	    original_stkbase = &foo;
	    (void)alloca (INITIAL_STK_OFFSET);
	}
	Main (ac, av);
	/*NOTREACHED*/
    }

Yes, I know, this is probably not portable to all existing machine
architectures.  But the feature for which this functionality is
required (creation of an executable from the running program) is
inherently non-portable itself.  (Of course, this version of
main() can be un-#ifdef-ed on systems where "dumping" cannot be
supported; a conventional main() is included.)

Regards,
--
    Oliver Laumann, Technical University of Berlin, Germany.
    pyramid!tub!net   net@TUB.BITNET   net@tub.cs.tu-berlin.de