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Message-ID: <3C63B0A1.8080805@syntrex.com>
Date: Fri, 08 Feb 2002 12:04:01 +0100
From: Pavel Tsekov <ptsekov AT syntrex DOT com>
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To: PsychoSphere <psychosphere2k AT yahoo DOT com>
CC: cygwin AT cygwin DOT com, kent AT watsen DOT net
Subject: Re: dlopen(0, RTLD_LAZY) doesn't work?
References: <20020208105224 DOT 24662 DOT qmail AT web13507 DOT mail DOT yahoo DOT com>
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PsychoSphere wrote:

> This is wrong... the .def file is never used when gcc
> is not linking a shared lib. You can see this by using
> a nonsense .def file, no errors are reported unless
> -shared is use

> 
> I believe the __declspec(...) has a similar effect, in
> that it is ignored unless -shared is specified, or
> -mdll is used.


Ok, I didn't know that, but hey ... you learn almost every day
something new :)


> Also, the dllimport directive is never used unless an
> import library is created and used, which is not the
> idea here.


Well, that was my point - if you use dllexport you must
use dllimport, not LoadLibrary. Or maybe you can use it
but you must use the correct name - something like
__imp_foo_something and not just foo.


> The problem i beleive, is that gcc is unaware that the
> exe is going to be opened as a shared lib. I have some


Well, maybe this is the real problem - perhaps someone else
would comment too.



> 
> Stephano Mariani
> 
> Well, I think the problem is that you specify
> __declspec(dllexport) in
> the function declaration. If you do this then you're
> supposed to do
> extern __declspec(dllimport) void foo(void) in the
> source file
> which uses this function. If you want to use load
> library you have to
> remove the __declspec(dllexport) and replace it with
> an .def with
> EXPORTS section, then you list the exports in the .def
> file.
> 
> just my 0.02 euro cents :P
> 
> Larry Hall (RFK Partners, Inc) wrote:
> 
> 
>>I've never seen this attempted to access a function
>>
> not in a DLL, though
> 
>>in theory (at least), what you're doing should work.
>>
>  
> 
>>Check the symbols in the resulting object file. 
>>
> Make sure that the call
> 
>>type is the same as you're referencing the function
>>
> by.  In other words,
> 
>>make sure that you call the function by the name as
>>
> the object file has
> 
>>it (probably stdcall) rather than the name as you
>>
> write it (cdecl).  
> 
>>Change your definition call type or the calling name
>>
> itself so that the 
> 
>>call type matches.  This might help.
>>
>>Larry Hall                             
>>
> lhall AT rfk DOT com
> 
>>RFK Partners, Inc.                     
>>
> http://www.rfk.com
> 
>>838 Washington Street                   (508)
>>
> 893-9779 - RFK Office
> 
>>Holliston, MA 01746                     (508)
>>
> 893-9889 - FAX
> 
>>
>>
>>At 09:57 PM 2/6/2002, Kent Watsen wrote:
>>
>>
>>
>>>OK, so I've written the windows equivalent of my
>>>
> original program
> 
>>>and still get the same error - is there some linking
>>>
> option I'm missine?
> 
>>>Here is the new code, again just compile (gcc foo.c)
>>>
> and run (foo.exe):
> 
>>>#include <stdio.h>
>>>#include <windows.h>
>>>
>>>extern __declspec(dllexport) void foo(void)
>>>{
>>>  printf("hello\n");
>>>}
>>>
>>>int main(int argc, char *argv[])
>>>{
>>>  void* dl   = NULL;
>>>  void* func = NULL;
>>>
>>>  dl = (void *) GetModuleHandle (NULL);
>>>  if (dl == NULL) {
>>>      printf("GetModuleHandle() failed\n");
>>>      exit(0);
>>>  }
>>>
>>>  func = (void*)GetProcAddress((HMODULE)dl, "foo");
>>>  if (func == NULL) {
>>>      printf("GetProcAddress() failed (code %u)\n",
>>>
> GetLastError());
> 
>>>      exit(0);
>>>  }
>>>
>>>  printf("do something meaningful\n");
>>>
>>>  return 0;
>>>}
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>Kent Watsen wrote:
>>>
>>>
>>>
>>>>Hi,
>>>>
>>>>I've read the mailing list archives and searched
>>>>
> google trying
> 
>>>>to figure out how to get the following program to
>>>>
> work.  All
> 
>>>>you have to do is save it to a file (foo.c),
>>>>
> compile (gcc foo.c),
> 
>>>>and run - I always get "dlsym() failed."
>>>>
>>>>Note, I have tried many variations of extern and
>>>>
> _declspec
> 
>>>>as well as looking for "_foo" in addition to "foo"
>>>>
> ("nm a.exe |
> 
>>>>grep foo" returned "0040104c T _foo"...
>>>>
>>>>Here is the code - help would be greatly
>>>>
> appreciated - thanks!
> 
>>>>#include <stdio.h>
>>>>#include <dlfcn.h>
>>>>#include <windows.h>
>>>>
>>>>extern __declspec(dllexport) void foo(void)
>>>>{
>>>>  printf("hello\n");
>>>>}
>>>>
>>>>int main(int argc, char *argv[])
>>>>{
>>>>  void* dl    = NULL;
>>>>  void* func = NULL;
>>>>
>>>>  dl = dlopen(0 , RTLD_LAZY);
>>>>  if (dl == NULL) {
>>>>      printf("dlopen() failed\n");
>>>>      exit(0);
>>>>  }
>>>>
>>>>  func = dlsym(dl, "foo");
>>>>  if (func == NULL) {
>>>>      printf("dlsym() failed\n");
>>>>      exit(0);
>>>>  }
>>>>
>>>>  printf("do something meaningful\n");
>>>>
>>>>  dlclose(dl);
>>>>  return 0;
>>>>}
>>>>
>>>>
>>>>
>>>>
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