Path: utzoo!attcan!uunet!mcvax!jack
From: jack@cwi.nl (Jack Jansen)
Newsgroups: comp.unix.wizards
Subject: Re: back to the (ivory) tower
Message-ID: <367@piring.cwi.nl>
Date: 11 Jun 88 15:00:52 GMT
References: <16018@brl-adm.ARPA> <1121@X.UUCP>
Organization: AMOEBA project, CWI, Amsterdam
Lines: 17

I think alloca() should be implementable on all architectures, even
those with a 'virtual stackpointer' (i.e. those where the compiler
knows that the stackpointer will always be fp+NNN (or the other way
around, for that matter)).

I trick I once used was to allocate the memory on the heap,
allocate two extra words, use one of them to build a linked list of
all alloca-blocks within the scope and (here comes the trick) store the
original return address in the other one, and replace the return address
by the address of a routine that will free alloca() blocks and then
really return.

The only problem is setjump/longjump, but these can probably be
massaged to handle the alloca blocks.
-- 
	Jack Jansen, jack@cwi.nl (or jack@mcvax.uucp)
	The shell is my oyster.