Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!uflorida!novavax!proxftl!bill
From: bill@proxftl.UUCP (T. William Wells)
Newsgroups: comp.lang.c
Subject: Re: Any way to catch exit()?
Keywords: _cleanup
Message-ID: <657@proxftl.UUCP>
Date: 29 Aug 88 07:05:11 GMT
References: <8808261432.AA11635@ucbvax.Berkeley.EDU> <967@cbnews.ATT.COM> <771@philmds.UUCP>
Reply-To: bill@proxftl.UUCP (T. William Wells)
Organization: Proximity Technology, Ft. Lauderdale
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In article <771@philmds.UUCP> leo@philmds.UUCP (Leo de Wit) writes:
:                                               Probably has something to
: do with keeping binary sizes small,

Yes.  Loading the stdio _cleanup means loading a substantial part
of stdio as well.

:                                     but I can't figure out how you can
: have several _cleanup() 's in one library. Anyone knows?
:
:                                Leo.

This is easy on a UNIX system.  You define __iob or whatever the
FILE pointers point to in the file where you want the fancy
_cleanup routine to go.  You then place the exit and then the
dummy _cleanup right after it.  You have to give the two object
files different names, but that is easy.  The names I have seen
are cleanup.o and fakcu.o.  So, if the program references stdio
anywhere, it will reference __iob.  When the linker finds the
first _cleanup, it will load it because of the __iob.  Then exit
comes along and uses the already loaded _cleanup so the second
one is ignored.  On the other hand, if stdio is not referenced,
the first _cleanup is ignored because there is no reference to
it; the exit is loaded because every program references exit, and
that forces the loading of the second _cleanup.

There are several variations on this theme, but as far as I know
they all depend on library ordering tricks.

---
Bill
novavax!proxftl!bill