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Date: Mon, 2 Aug 1999 23:53:16 +0100
From: "Gary V. Vaughan" <gary AT oranda DOT demon DOT co DOT uk>
To: cygwin AT sourceware DOT cygnus DOT com
Cc: Steve McAndrewSmith <steve AT finagle DOT org>
Subject: Re: [Q]: Linking against DLLs.
Message-ID: <19990802235316.A10952@demon.co.uk>
References: <37A5CECC DOT 54A4236C AT finagle DOT org> <19990802204446 DOT C9936 AT demon DOT co DOT uk>
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In-Reply-To: <19990802204446.C9936@demon.co.uk>; from Gary V. Vaughan on Mon, Aug 02, 1999 at 08:44:46PM +0100
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On Mon, Aug 02, 1999 at 10:01:00AM -0700, Steve McAndrewSmith wrote:
> I would think that this would be a FAQ (and forgive me if it is, and I
> just haven't seen it), but how do you link against thrid-party DLLs? 
> CygWin includes import libraries for most/all of the standard Win32
> libraries, but what would it take to make an import library for any
> random DLL? 

There is some code I use in libtool for that very purpose (adapted from
code written by DJ Delorie for the next version of binutils).  Incase
you have trouble finding it (it is hidden inside the libtool script),
and for the benefit of the mail archives, I have extracted a copy and
attached.  This time for real... sorry folks.

Cheers,
	Gary.
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/* impgen.c starts here */
/*   Copyright (C) 1999 Free Software Foundation, Inc.

 This file is part of GNU libtool.

 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 2 of the License, or
 (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include <stdio.h>		/* for printf() */
#include <unistd.h>		/* for open(), lseek(), read() */
#include <fcntl.h>		/* for O_RDONLY, O_BINARY */
#include <string.h>		/* for strdup() */

/* O_BINARY isn't required (or even defined sometimes) under Unix */
#ifndef O_BINARY
#define O_BINARY 0
#endif

static unsigned int
pe_get16 (fd, offset)
     int fd;
     int offset;
{
  unsigned char b[2];
  lseek (fd, offset, SEEK_SET);
  read (fd, b, 2);
  return b[0] + (b[1]<<8);
}

static unsigned int
pe_get32 (fd, offset)
    int fd;
    int offset;
{
  unsigned char b[4];
  lseek (fd, offset, SEEK_SET);
  read (fd, b, 4);
  return b[0] + (b[1]<<8) + (b[2]<<16) + (b[3]<<24);
}

static unsigned int
pe_as32 (ptr)
     void *ptr;
{
  unsigned char *b = ptr;
  return b[0] + (b[1]<<8) + (b[2]<<16) + (b[3]<<24);
}

int
main (argc, argv)
    int argc;
    char *argv[];
{
    int dll;
    unsigned long pe_header_offset, opthdr_ofs, num_entries, i;
    unsigned long export_rva, export_size, nsections, secptr, expptr;
    unsigned long name_rvas, nexp;
    unsigned char *expdata, *erva;
    char *filename, *dll_name;

    filename = argv[1];

    dll = open(filename, O_RDONLY|O_BINARY);
    if (!dll)
	return 1;

    dll_name = filename;
  
    for (i=0; filename[i]; i++)
	if (filename[i] == '/' || filename[i] == '\\'  || filename[i] == ':')
	    dll_name = filename + i +1;

    pe_header_offset = pe_get32 (dll, 0x3c);
    opthdr_ofs = pe_header_offset + 4 + 20;
    num_entries = pe_get32 (dll, opthdr_ofs + 92);

    if (num_entries < 1) /* no exports */
	return 1;

    export_rva = pe_get32 (dll, opthdr_ofs + 96);
    export_size = pe_get32 (dll, opthdr_ofs + 100);
    nsections = pe_get16 (dll, pe_header_offset + 4 +2);
    secptr = (pe_header_offset + 4 + 20 +
	      pe_get16 (dll, pe_header_offset + 4 + 16));

    expptr = 0;
    for (i = 0; i < nsections; i++)
    {
	char sname[8];
	unsigned long secptr1 = secptr + 40 * i;
	unsigned long vaddr = pe_get32 (dll, secptr1 + 12);
	unsigned long vsize = pe_get32 (dll, secptr1 + 16);
	unsigned long fptr = pe_get32 (dll, secptr1 + 20);
	lseek(dll, secptr1, SEEK_SET);
	read(dll, sname, 8);
	if (vaddr <= export_rva && vaddr+vsize > export_rva)
	{
	    expptr = fptr + (export_rva - vaddr);
	    if (export_rva + export_size > vaddr + vsize)
		export_size = vsize - (export_rva - vaddr);
	    break;
	}
    }

    expdata = (unsigned char*)malloc(export_size);
    lseek (dll, expptr, SEEK_SET);
    read (dll, expdata, export_size);
    erva = expdata - export_rva;

    nexp = pe_as32 (expdata+24);
    name_rvas = pe_as32 (expdata+32);

    printf ("EXPORTS\n");
    for (i = 0; i<nexp; i++)
    {
	unsigned long name_rva = pe_as32 (erva+name_rvas+i*4);
	printf ("\t%s @ %ld ;\n", erva+name_rva, 1+ i);
    }

    return 0;
}
/* impgen.c ends here */


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