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From: "Stephano Mariani" <sk DOT mail AT btinternet DOT com>
To: "'Kent Watsen'" <kent AT watsen DOT net>, <cygwin AT cygwin DOT com>
Subject: RE: dlopen(0, RTLD_LAZY) doesn't work?
Date: Thu, 7 Feb 2002 20:01:56 -0000
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In my experience, this is probably because the linker (or cc1) insists
on eliminating "dead code", since it is never (directly) called.

I have managed to overcome this by using:

#include <stdio.h>
#include <dlfcn.h>
#include <windows.h>

__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;
}

and compiling with first:
gcc -mdll foo.c -c -o ...
then linking without -mdll:
gcc foo.o ... -o foo


Note: I have not tried this, but I have previously used
dlopen(NULL,RTLD_LAZY) successfully. Also, I do not think that you can
call printf() without first attaching to the console within your
dlopened routine.

Stephano Mariani

-----Original Message-----
From: cygwin-owner AT cygwin DOT com [mailto:cygwin-owner AT cygwin DOT com] On Behalf
Of Kent Watsen
Sent: Thursday, 7 February 2002 2 57
To: cygwin AT cygwin DOT com
Subject: Re: dlopen(0, RTLD_LAZY) doesn't work?


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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