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Path: utzoo!mnetor!seismo!rutgers!pyrnj!mirror!ima!haddock!karl
From: karl@haddock.UUCP (Karl Heuer)
Newsgroups: comp.lang.forth
Subject: Re: Unix system calls from Forth
Message-ID: <182@haddock.UUCP>
Date: Wed, 3-Dec-86 22:55:47 EST
Article-I.D.: haddock.182
Posted: Wed Dec  3 22:55:47 1986
Date-Received: Thu, 4-Dec-86 03:06:36 EST
References: <12234@watnot.UUCP>
Reply-To: karl@haddock.ISC.COM.UUCP (Karl Heuer)
Distribution: net
Organization: Interactive Systems, Boston
Lines: 27

In article <12234@watnot.UUCP> ccplumb@watnot.UUCP (Colin Plumb) writes:
>I'm working on a 32-bit Forth for a VAX under BSD 4.2 Unix.
>I'm trying to figure out how to implement the system call interface.

Well, I've already done it on SysV, and I think the same idea should work
on BSD.  On success, the return values (0, 1, or 2 of them) and a success
indicator are placed on the stack; on failure, only the failure indicator.
(I used 1 for ok vs. 0 for error, but 0 for ok would've made it easier to
test.)  The error code can be retrieved via "errno" (which is not a variable
because I didn't think it needed to be user-writable); I didn't leave it on
the stack because most of the time it isn't needed.  For consistency, even
calls that never fail (e.g. getpid) have the flag on top.  (I also defined
a word which drops the top of stack and bombs with an appropriate message
if it was a failure.)

I used a leading "$" (so "$dup" is a system call, while "dup" is a Forth
word), or "$_" for the "real" system call if the C interface twiddles it
(so $_getpid returns two values, while $getpid and $getppid select the one
of interest).  I didn't do this with $pipe and $wait; they just return two
values (too bad C can't do that!  Returning a struct by value doesn't count).

I used one defining word which takes three arguments (number of arguments,
number of results, and chmk number), and had one chunk of common code in
assembly language.  The asm code was the only part I needed to rewrite when
I ported my TIL to a 3b2.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint