Newsgroups: comp.unix.aix
Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!mit-eddie!bloom-beacon!world!madd
From: madd@world.std.com (jim frost)
Subject: Re: changing the console; alloca missing from 9021?
Message-ID: <1990Aug7.022021.20827@world.std.com>
Organization: Saber Software
References: <61875@bu.edu.bu.edu> <3017@awdprime.UUCP>
Date: Tue, 7 Aug 90 02:20:21 GMT

kent@opus.austin.ibm.com (Kent Malave') writes:
>> Also, it looks like alloca isn't in libbsd.a or libc.a.  Was this just an
>> oversight in this release?  If this is true, is there someone who can give
>> me a copy (hello IBM?)
>>
>	You may want to look in /usr/lpp/bos.  In this directory there are
>	to very good articles on AIX and BSD differences in system administration
>	(file bsdadm) and porting of code (file bsdport).

The bsdport file is pretty good, if you're porting bsd code I
recommend it.  There are still some gotchas, though.

First gotcha is you need to include #pragma alloca to get alloca.
It's pretty hard to build a function that does alloca on a lot of
machines (the rios is one of them) so it's done inline.  It also uses
an extra register because it keeps both a stack pointer (r1) and a
frame pointer (r31) so you get moderately less efficient code.

Second gotcha is that if you're using /lib/cpp as recommended in
bsdport, #pragma alloca will cause it to internal error.  You can do
this in one line:

	% cat > foo.c
	#pragma alloca
	^D
	% cc -B/lib/ foo.c # bsdcc from bsdport does this
	[some number] Internal error -- please contact your IBM representative.

I might be wrong about the -B flag, I don't have the documentation
handy and it might be some other letter.  The internal cpp doesn't
internal error.  It does, however, barf on at-signs (@) which is
hardly nice behavior.

On the up-side, compatibility with BSD code seems very high.  About
the only problem I had on the stuff I have ported was that sigcontext
(mstsave or whatever on the rios) is radically different and that
compiling in BSD mode is pretty slow.

Happy hacking,

jim frost
saber software
jimf@saber.com