Path: utzoo!attcan!uunet!husc6!necntc!ames!oliveb!sun!thetone!swilson
From: swilson%thetone@Sun.COM (Scott Wilson)
Newsgroups: comp.lang.c
Subject: Re: alloca wars
Message-ID: <63153@sun.uucp>
Date: 6 Aug 88 01:37:04 GMT
References: <62721@sun.uucp> <394@mfgfoc.UUCP>
Sender: news@sun.uucp
Reply-To: swilson@sun.UUCP (Scott Wilson)
Organization: Sun Microsystems, Mountain View
Lines: 38

In article <394@mfgfoc.UUCP> exodus@mfgfoc.UUCP (Greg Onufer) writes:
>On a M68k with a decent OS, alloca is not more than a few lines of assembly
>code, correct?  (Judging by the size of the GNU assembly alloca)...
>If one needs alloca and it is not available, why not write a quick alloca?

This makes about as much sense as saying:  If your in Tokyo and need
to get to the airport just ask directions.  It's only one sentence, how
hard can that be?  Well if you don't know the language it's probably
pretty damn hard.  I would guess the same is true about writing m68k
code, if you don't know how it doesn't matter if it is just a few lines.

Ok, so I need to write alloca, so let's see I brush up on m68k, buy the
book if necessary, understand the calling convention and stack frame
stuff for my compiler, figure out if my programming environment has
an easy way to get assembler in, understand the particular enviroment's
assembler syntax, etc.  Gee that should only take 10-15 minutes.  We're
talking about C here, I think it's unreasonable to expect a programmer
to have any knowledge of assembly code to port a program.  What may
seem like a simple exercise to you and others may be a major chore
for me and others.  And after all the debate on here about alloca 
implementation difficulties, I would be hesitant to try it on a cpu that
it hasn't already been done for in fear that it be impossible.  And what
if I'm not running on a 68k?  C runs under many OS's and many cpu's some
you've never heard of.  I've written C code for a TP1 running MOST, how
do I do alloca there?  The best assembler manual for it is in Japanese.
It took me quite a while to write setjmp/longjmp for this beast, it would
be just as much of a hassle to write alloca.  Isn't that what languages like
C are all about, so I don't have to know assembly language?

Again let me say that this whole discussion started with regard to
portability.  Your solution is to add machine dependent code to a
program to make it work.  So how does that help future portability?
It doesn't of course.

--
Scott Wilson		arpa: swilson@sun.com
Sun Microsystems	uucp: ...!sun!swilson
Mt. View, CA