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From: rmtodd@uokmax.UUCP (Richard Michael Todd)
Newsgroups: comp.os.minix
Subject: Re: More on sh/shar
Message-ID: <581@uokmax.UUCP>
Date: Sat, 30-May-87 22:01:49 EDT
Article-I.D.: uokmax.581
Posted: Sat May 30 22:01:49 1987
Date-Received: Tue, 2-Jun-87 01:15:48 EDT
References: <1643@encore.UUCP>
Organization: University of Oklahoma, Norman, OK
Lines: 33
Summary: UNIX and non-UNIX linkers handle global vars differently

In article <1643@encore.UUCP>, paradis@encore.UUCP (Jim Paradis) writes:
> Remember my last message complaining about /bin/sh being unable to
> unpack "real" shell archives?  Well, last night I got SO sick&tired
> of the situation that I took a deep breath and dove head-first into
> the code for /bin/sh.  Getting it to compile was a feat unto itself...
> (seems the MINIX compiler handles globals and externs differently
> from the PC/IX compiler...). 
Yep.  Actually it's a difference between how UNIX-type linkers (of which
PC/IX's is apparently one) and most everybody else's handle globals.
Under UNIX, you can have multiple files each with a global var. defined,
say:
file foo.c:
	int a;
...

file bar.c:
	int a;
...
and the UNIX linker will see the variable declared multiple times in the
modules and allocate space in the result file only once.  Most other linkers
consider duplicate variable declarations to be errors.  For C programs
on those systems, the global definition can appear in only one file, and
the other files must use extern declarations (e.g. "extern int a;").
On a side note, I've also gotten the shell to recompile, both under MINIX
and under Aztec C (running the output thru dos2out).  I changed all the 
offending definitions in sh.h (which gets included in every file) to
read "EXTERN int whatever;" and #defined EXTERN extern in every file except
one.  Very minimal changes were needed to get it to compile under Aztec
C after I'd gotten it to compile under MINIX cc.
--------------------------------------------------------------------------
Richard Todd
USSnail:820 Annie Court,Norman OK 73069
UUCP: {allegra!cbosgd|ihnp4}!okstate!uokmax!rmtodd