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From: alan@ecrcvax.UUCP (Alan P. Sexton)
Newsgroups: comp.unix.wizards
Subject: Re: ld -A (incremental loading)
Message-ID: <437@ecrcvax.UUCP>
Date: Mon, 5-Oct-87 04:17:08 EDT
Article-I.D.: ecrcvax.437
Posted: Mon Oct  5 04:17:08 1987
Date-Received: Fri, 9-Oct-87 02:25:23 EDT
References: <465@tasis.utas.oz>
Reply-To: alan@ecrcvax.UUCP (Alan P. Sexton)
Followup-To: comp.unix.wizards
Distribution: world
Organization: ECRC, Munich 81, West Germany
Lines: 159
Keywords: 4.2BSD 4.3BSD incremental dynamic loading linking
Summary: How to do it.

In article <465@tasis.utas.oz> greg@tasis.utas.oz (Greg Watson) writes:
>A question for the 4.2BSD gurus:
>
>Has anyone played around with (and got working) the -A flag with 'ld'?
>This flag (according to the manual) provides incremental loading and
>allows an object to be loaded into an already executing program.
>
>It doesn't seem to be well documented anywhere that I can find. Has anyone
>got a simple test program that uses this feature?
>
>Thanks,
>
>Greg Watson
>
#! /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:
#	README
#	Makefile
#	main.c
#	tst.c
# This archive created: Mon Oct  5 09:12:25 1987
export PATH; PATH=/bin:$PATH
echo shar: extracting "'README'" '(316 characters)'
if test -f 'README'
then
	echo shar: will not over-write existing file "'README'"
else
sed 's/^X//' << \SHAR_EOF > 'README'
XHow to do Dynamic loading in BSD4.[23]
X
XInstructions:
X	run make
X	run main
X	output should be similar to the following:
X
Xmain
Xcurrend = 000033fc
X/bin/ld -N -A main -T 33fc tst.o -o tmpfil -lc
Xreadsize = 200
Xreadsize = 512, entry = 00000000, currend = 000033fc
X
XThis line was printed by a dynamically loaded subroutine
SHAR_EOF
if test 316 -ne "`wc -c < 'README'`"
then
	echo shar: error transmitting "'README'" '(should have been 316 characters)'
fi
fi # end of overwriting check
echo shar: extracting "'Makefile'" '(76 characters)'
if test -f 'Makefile'
then
	echo shar: will not over-write existing file "'Makefile'"
else
sed 's/^X//' << \SHAR_EOF > 'Makefile'
Xall:	main tst.o
X
Xmain:	main.c
X	cc -o main main.c
X
Xtst.o:	tst.c
X	cc -c tst.c
SHAR_EOF
if test 76 -ne "`wc -c < 'Makefile'`"
then
	echo shar: error transmitting "'Makefile'" '(should have been 76 characters)'
fi
fi # end of overwriting check
echo shar: extracting "'main.c'" '(1201 characters)'
if test -f 'main.c'
then
	echo shar: will not over-write existing file "'main.c'"
else
sed 's/^X//' << \SHAR_EOF > 'main.c'
X#include <stdio.h>
X#include <a.out.h>
X
X#define round(x,s) ((((x)-1) & ~((s)-1)) + (s))
X
Xextern char	*sbrk() ;
X
Xmain()
X{
X	int	i, fd, readsize ;
X	struct exec	header ;
X	char	buf[512], *currend ;
X	int	(*f)() ;
X	
X	printf("main\n") ;
X	currend = sbrk(0) ;
X	printf("currend = %08x\n", currend) ;
X	sprintf(buf,"/bin/ld -N -A main -T %x tst.o -o tmpfil -lc", currend);
X	printf(buf) ;
X	putchar('\n') ;
X	if (i = system (buf))
X	{
X		printf("error: system returned %x\n", i) ;
X		exit() ;
X	}
X	if ((fd = open("tmpfil", 0)) <0)
X	{
X		printf("can't open tmpfil\n") ;
X		exit() ;
X	}
X	if (read(fd, (char *)&header, sizeof(header)) <= 0)
X	{
X		printf (" error in reading header of new a.out\n") ;
X		exit() ;
X	}
X	readsize = round(header.a_text,4) + round(header.a_data,4);
X	readsize = round(readsize+header.a_bss, 512) ;
X	printf("readsize = %x\n", readsize) ;
X	if (sbrk(readsize) == 0)
X	{
X		printf("error: cannot sbrk %d bytes\n", readsize) ;
X		exit() ;
X	}
X	if (readsize != read(fd, currend, readsize))
X	{
X		printf("error: cannot read %d bytes\n", readsize) ;
X		exit() ;
X	}
X	printf ("readsize = %d, entry = %08x, currend = %08x\n",
X			readsize, header.a_entry, currend) ;
X	f = (int (*)())(currend+header.a_entry) ;
X	(*f)() ;
X}
SHAR_EOF
if test 1201 -ne "`wc -c < 'main.c'`"
then
	echo shar: error transmitting "'main.c'" '(should have been 1201 characters)'
fi
fi # end of overwriting check
echo shar: extracting "'tst.c'" '(84 characters)'
if test -f 'tst.c'
then
	echo shar: will not over-write existing file "'tst.c'"
else
sed 's/^X//' << \SHAR_EOF > 'tst.c'
Xtry()
X{
X	printf("\nThis line was printed by a dynamically loaded subroutine\n") ;
X}
SHAR_EOF
if test 84 -ne "`wc -c < 'tst.c'`"
then
	echo shar: error transmitting "'tst.c'" '(should have been 84 characters)'
fi
fi # end of overwriting check
#	End of shell archive
exit 0


-- 
Alan Sexton				ECRC, Arabellastr 17,
alan@ecrcvax.UUCP			8000 Muenchen 81, West Germany
mcvax!unido!ecrcvax!alan		tel. (089) 92699164