Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!purdue!haven!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.questions
Subject: Re: help needed in cc library search order
Keywords: cc ld library search
Message-ID: <17328@mimsy.UUCP>
Date: 5 May 89 22:58:59 GMT
References: <176@larry.sal.wisc.edu>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 39

In article <176@larry.sal.wisc.edu> jwp@larry.sal.wisc.edu
(Jeffrey W Percival) writes:
>... Case 2: cc main.o lib2.a lib1.a

>The mystery:  I would have thought that I would get low2() always,
>because lib2 preceeds lib1.  HOWEVER,  I get low1() unless I
>make a call to low2() in main().  In other words, the linker
>chooses differently depending on whether main() makes a call to low().

The linker acts differently when reading a library than when reading
a `.o' file.  If you say

	ld /lib/crt0.o main.o low.o lib1.a	# or `cc' instead of `ld'

you will get your second version of low().  But when you say

	ld /lib/crt0.o main.o lib2.a lib1.a

you are telling ld `read main.o, then *scan* lib2.a, then scan lib1.a'
---so ld scans it, looking for any symbols it happens to need just then,
and finds none.  It closes lib2 and goes on to lib1, where it finds
mid() and *now* discovers it needs low().  It does *not* stop, back
up to lib2, look again, and find the low() there; ld *never* `backs
up'.  If there were no low() in lib1, it would complain `_low undefined'.

What you need to do, then, is convince ld to pull low() out of lib2
anyway, whether it really needs it or not.  There is a simple way
to do this:

	ld -u _low /lib/crt0.o main.o lib2.a lib1.a

The `-u' flag tells ld `make this an undefined symbol'.  Thus, when it
comes across low() in lib2, it will take it immediately.

`cc' might accept -u, or might not; if not, you will have to run
ld directly (and append -lc to tell it to search the C library).
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris