Message-ID: <486CE4BF.9040409@users.sourceforge.net>
Date: Thu, 03 Jul 2008 09:39:59 -0500
From: "Yaakov (Cygwin Ports)" <yselkowitz AT users DOT sourceforge DOT net>
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To: cygwin AT cygwin DOT com
Subject: binutils: ld --export-dynamic
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cgf,

While you're waiting for the binutils list to get back to you, here's
another binutils issue.  This is not a regression in 2.18, but rather a
longstanding difference in Cygwin behaviour versus Linux.

When linking a program with -Wl,--export-dynamic, no symbols are
exported.  The problem arises when the executable needs to either dlopen
itself, or when it has plugins which are "linked" against it.  Both
scenarios are not uncommon, particularly with GNOME software.

While this does work on Linux, it does not work on Cygwin with
- --export-dynamic; only --export-all-symbols, an i386PE-specific flag,
will accomplish this.

I've attached a test case; it's a simplified version of the test used in
LT_SYS_DLOPEN_SELF (prev. AC_LIBTOOL_DLOPEN_SELF):

$ gcc -o test.exe dlopen-self.c && ./test.exe
status = 0

$ gcc -Wl,--export-dynamic -o test.exe dlopen-self.c && ./test.exe
status = 0

$ gcc -Wl,--export-all-symbols -o test.exe dlopen-self.c && ./test.exe
status = 1

Running 'objdump -p test.exe' will also show that the export table is
only generated in the last case.

I would appreciate your input on this issue.


Yaakov
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#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>

#define LT_DLUNKNOWN		0
#define LT_DLNO_USCORE		1
#define LT_DLNEED_USCORE	2

void
fnord()
{
  int i=42;
}

int
main ()
{
  void *self = dlopen (0, RTLD_GLOBAL|RTLD_LAZY);
  int status = LT_DLUNKNOWN;

  if (self)
    {
      if (dlsym (self,"fnord"))          status = LT_DLNO_USCORE;
      else if (dlsym( self,"_fnord"))    status = LT_DLNEED_USCORE;
    }
  else
    puts (dlerror ());

	printf ("status = %i\n", status);
    exit (0);
}


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