Mail Archives: cygwin/2002/02/07/15:06:07
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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