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From: law@petsd.UUCP (Steve Law)
Newsgroups: net.lang.c,net.unix
Subject: Re: Creating functions in data space
Message-ID: <728@petsd.UUCP>
Date: Mon, 10-Mar-86 13:26:14 EST
Article-I.D.: petsd.728
Posted: Mon Mar 10 13:26:14 1986
Date-Received: Wed, 12-Mar-86 03:09:56 EST
Organization: Concurrent Computer Corp.
Lines: 54
Xref: watmath net.lang.c:8118 net.unix:7348

> In response to George Tomasevich:
> 
I had missed that one.

> This seems to me to be very machine dependent, even compiler
> dependent. I'm sure that the compiler, in any event, would spit all
> kinds of warnings at you. Perhaps a way around it would be to gain
> access somehow to the memory management register, have a function that
> flips a bit just before calling the data code, and cleans up afterwards.
> Perhaps the problem is that C allows you to have identically named
> functions and variables, but you could get around that as well.
> 
UNIX System V link editor (ld) allows one to put functions in the .data
section of a COFF file.  All you need to do is to create a ld command
file (also called ifile).  For example, the following ifile:

     SECTIONS {
     	 .data: {
     		file1.o (.text)   /* file1.c, file2.c file3.c contain */
     	        file2.o (.text)   /* the functions text that to be    */
     	        file3.o (.text)   /* placed in the .data section of   */
     	        ...               /* the final a.out                  */
     	        }
     	 }

and the following command lines:

     cc -c file1.c file2.c file3.c
     cc -N otherfiles.c ifile

will create an a.out which will have all the functions of file[123].c in
the .data section instead of .text section.  One can also use ifile(s) to
do the following:

     - place data in .text
     - create dummy sections (e.g., store history info)
     - create holes within sections
     - align sections
     - merge sections
     - subsystem linking

and many others.  It is a very powerful tool, but some of its features
are not well documented!!!

				Steve Law

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