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In-Reply-To: Your message of "Fri, 02 Oct 1998 19:06:35 +0900 (JST)"
	<19981002190635P.shiozaki@ased.mt.nec.co.jp>
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Date: Fri, 02 Oct 1998 22:41:40 +0900
From: Masanori Kanaoka <kana@saijo.mke.mei.co.jp>
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Subject: [FreeBSD-tech-jp 1749] Re: What's ELF
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$B6b2,!w>>2<<wEE;R9)6H$G$9!#(B

$ $B1v:j!wF|K\EE5$$G$9!#2O4_$r(B tech-jp $B$K0\$7$^$9$M!#(B

$ $B;d$NAGKQ$J5?Ld!'(B
$   1. $B$J$s$G(B -1 $B$8$c$J$/$F(B 1 $B$J$N!)(B
$   2. $B$J$s$G(B foo $B$H(B _foo $B$GCM$,0c$&$N!)(B

$B8+$k$Y$-$H$3$m$,0c$&$N$+$b!";d$NFI$_0c$($+$b$7$l$^$;$s!#(B
$BD9$/$J$j$^$9$,!"(B/usr/src/lib/libc/gen/dlfcn.c $B$r0zMQ$7$^$9!#(B

----------------- /usr/src/lib/libc/gen/dlfcn.c -----------------------
/*-
 * Copyright (c) 1998 John D. Polstra
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	$Id: dlfcn.c,v 1.2 1998/03/07 19:57:05 jdp Exp $
 */

/*
 * Linkage to services provided by the dynamic linker.  These are
 * implemented differently in ELF and a.out, because the dynamic
 * linkers have different interfaces.
 */

#ifdef __ELF__

#include <dlfcn.h>
#include <stddef.h>

static const char sorry[] = "Service unavailable";

/*
 * For ELF, the dynamic linker directly resolves references to its
 * services to functions inside the dynamic linker itself.  These
 * weak-symbol stubs are necessary so that "ld" won't complain about
 * undefined symbols.  The stubs are executed only when the program is
 * linked statically, or when a given service isn't implemented in the
 * dynamic linker.  They must return an error if called, and they must
 * be weak symbols so that the dynamic linker can override them.
 */

#pragma weak _rtld_error
void
_rtld_error(const char *fmt, ...)
{
}

#pragma weak dladdr
int
dladdr(const void *addr, Dl_info *dlip)
{
	_rtld_error(sorry);
	return 0;
}

#pragma weak dlclose
int
dlclose(void *handle)
{
	_rtld_error(sorry);
	return -1;
}

#pragma weak dlerror
const char *
dlerror(void)
{
	return sorry;
}

#pragma weak dlopen
void *
dlopen(const char *name, int mode)
{
	_rtld_error(sorry);
	return NULL;
}

#pragma weak dlsym
void *
dlsym(void *handle, const char *name)
{
	_rtld_error(sorry);
	return NULL;
}

#else /* a.out format */

#include <sys/types.h>
#include <nlist.h>		/* XXX - Required by link.h */
#include <dlfcn.h>
#include <link.h>
#include <stddef.h>

/*
 * For a.out, entry to the dynamic linker is via these trampolines.
 * They enter the dynamic linker through the ld_entry struct that was
 * passed back from the dynamic linker at startup time.
 */

/* GCC is needed because we use its __builtin_return_address construct. */

#ifndef __GNUC__
#error "GCC is needed to compile this file"
#endif

/*
 * These variables are set by code in crt0.o.  For compatibility with
 * old executables, they must be common, not extern.
 */
struct ld_entry	*__ldso_entry;		/* Entry points to dynamic linker */
int		 __ldso_version;	/* Dynamic linker version number */

int
dladdr(const void *addr, Dl_info *dlip)
{
	if (__ldso_entry == NULL || __ldso_version < LDSO_VERSION_HAS_DLADDR)
		return 0;
	return (__ldso_entry->dladdr)(addr, dlip);
}

int
dlclose(void *handle)
{
	if (__ldso_entry == NULL)
		return -1;
	return (__ldso_entry->dlclose)(handle);
}

const char *
dlerror(void)
{
	if (__ldso_entry == NULL)
		return "Service unavailable";
	return (__ldso_entry->dlerror)();
}

void *
dlopen(const char *name, int mode)
{
	if (__ldso_entry == NULL)
		return NULL;
	return (__ldso_entry->dlopen)(name, mode);
}

void *
dlsym(void *handle, const char *name)
{
	if (__ldso_entry == NULL)
		return NULL;
	if (__ldso_version >= LDSO_VERSION_HAS_DLSYM3) {
		void *retaddr = __builtin_return_address(0); /* __GNUC__ only */
		return (__ldso_entry->dlsym3)(handle, name, retaddr);
	} else
		return (__ldso_entry->dlsym)(handle, name);
}

#endif /* __ELF__ */
----------------- /usr/src/lib/libc/gen/dlfcn.c -----------------------


$ 
$ $B$H$$$&$3$H$G!"$b$C$H9T57$NNI$$%W%m%0%i%`$G%F%9%H$7$F$_$F$/$@$5$$!'(B
$ 
$ bar.c
$ ---------
$ #include <stdio.h>
$ #include <dlfcn.h>
$ 
$ int
$ main(void)
$ {
$         void    *h = dlopen("./foo.so",RTLD_NOW);
$         int result;
$ 
$         result = dlsym(h, "foo") != NULL;
$         printf("foo = %d\n", result);
$         printf("%s\n",dlerror());
$ 
$         result = dlsym(h, "_foo") != NULL;
$         printf("_foo = %d\n", result);
$         printf("%s\n",dlerror());
$ 
$         return 0;
$ }
$ ====

$B>e5-(B bar.c -> bar1.c $B$HL>A0$rJQ$($F$d$C$F$_$^$7$?!#(B

$B7k2L$O0J2<$N$H$&$j$G$9!#(B

[current]% ./bar1
foo = 1
(null)
_foo = 0
Undefined symbol "_foo"



------- $B>>2<<wEE;R9)6H3t<02q<R(B  $B@>>r;v6HIt!!%`!<%S!<5;=QIt(B -------
$B!!6b2,!!@57{!!!!!!(BTEL:0897-56-1111($BFb(B518)  FAX:0897-56-8142
------------------ Masanori Kanaoka <kana@saijo.mke.mei.co.jp>----




