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Path: utzoo!mnetor!seismo!ut-sally!husc6!linus!ramsdell
From: ramsdell@linus.UUCP (John D. Ramsdell)
Newsgroups: comp.unix.wizards
Subject: Re: Dynamic function loading
Message-ID: <2773@linus.UUCP>
Date: Tue, 14-Apr-87 14:48:33 EST
Article-I.D.: linus.2773
Posted: Tue Apr 14 14:48:33 1987
Date-Received: Sun, 19-Apr-87 04:34:15 EST
References: <600@rdin.UUCP> <6448@bu-cs.BU.EDU>
Organization: The MITRE Corp., Bedford, MA
Lines: 83
Summary: Dynamic function loading



Here is a simple example giving the details of
dynamic function loading using ld -A.
John

#! /bin/sh
# This is a shell archive, meaning:
# 1. Remove everything above the #! /bin/sh line.
# 2. Save the resulting text in a file.
# 3. Execute the file with /bin/sh (not csh) to create the files:
#	dyn.c
#	fun.c
#	makefile
# This archive created: Tue Apr 14 14:36:34 1987
export PATH; PATH=/bin:$PATH
if test -f 'dyn.c'
then
	echo shar: will not over-write existing file "'dyn.c'"
else
cat << \SHAR_EOF > 'dyn.c'
/* Dynamically loads a function constructed using ld -A .. -T ... */
/* John D. Ramsdell -- April 1987 -- The MITRE Corporation. */
#include <stdio.h>
#include <sys/types.h>
#include <a.out.h>

typedef int (*intfun)();

caddr_t fun, sbrk();

caddr_t funload (fun)
     caddr_t fun;
{				/* Loads a function from a file. */
  FILE *obj; struct exec hdr[1]; int size;
  obj = fopen ("fun", "r");	/* Name hardwired in this example. */
  fread (hdr, sizeof(*hdr), 1, obj);
  size = hdr->a_text + hdr->a_data + hdr->a_bss;
  brk (fun);			/* Return of brk and sbrk should be checked. */
  fun = sbrk (size);		/* Allocate space. */
  fread (fun, size, 1, obj);	/* Load code. */
  fclose (obj);
  return fun;
}
  
main ()
{
  printf ("Start at 0x%lx.\n", sbrk (0));
  fun = (caddr_t) 0x25000;	/* Must be same number used in ld command. */
  printf ("Load at 0x%lx.\n", fun);
  fun = funload(fun);
  printf ("New end at 0x%lx.\n", sbrk (0));
  printf ("The answer is %d.\n", (*((intfun) fun))());
}
SHAR_EOF
fi # end of overwriting check
if test -f 'fun.c'
then
	echo shar: will not over-write existing file "'fun.c'"
else
cat << \SHAR_EOF > 'fun.c'
int dynamically_loaded_function ()
{
  return 42;
}
SHAR_EOF
fi # end of overwriting check
if test -f 'makefile'
then
	echo shar: will not over-write existing file "'makefile'"
else
cat << \SHAR_EOF > 'makefile'
all:	dyn fun

dyn:	dyn.o makefile
	cc -u _end -o $@ dyn.o

fun:	fun.o dyn makefile
	ld -A dyn -N -X -o fun -T 25000 fun.o -lc 
SHAR_EOF
fi # end of overwriting check
#	End of shell archive
exit 0