Path: utzoo!attcan!uunet!pcrat!rick
From: rick@pcrat.UUCP (Rick Richardson)
Newsgroups: comp.sys.intel
Subject: Re: function start address allignment
Keywords: word alignment
Message-ID: <687@pcrat.UUCP>
Date: 1 Mar 89 03:50:08 GMT
References: <311@ssp2.idca.tds.philips.nl>
Reply-To: rick@pcrat.UUCP (Rick Richardson)
Organization: PC Research, Inc., Tinton Falls, NJ
Lines: 25

In article <311@ssp2.idca.tds.philips.nl> pb@idca.tds.PHILIPS.nl (Peter Brouwer) writes:
>When looking at executables with sdb and dis (unix) I noticed that the
>start of a function in a c program is always word alligned. If
>My question is: Is this general for compilers/assemblers in unix environment
>on 80386 machines?

I think this is due to the Basic-16 ... iAPX286 ... iAPX386 heritage
of the compiler.  Basic-16 had a mechanism known as transfer vectors
that were a lousy substitute for medium model, but nice for doing
'patches' to individual modules at runtime.  The implementation,
I believe, required word alignment.  I think this saw heavy use
in AT&T's biggest software project and also in their products with
the undefinable new name.

Of course, those wasted bytes add up in a hurry.  I can recall being
short around 250 bytes of ROM and finding 300 bytes available by
deleting the alignment requests.  Even more hideous, though, is
to count the number of times a register half is zeroed when it
already contains zero.

-- 
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