Mayank Kaushik <mayank.utexas@xxxxxxxxx> writes:
>> > gcc -fPIC -fPIE -pie -o library.so test.c
>>
>> That does not make a shared library.
>
> I'm curious, why not? It's position independent. "file" says it's a
> shared object:
> $ file ./library.so
> ./library.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV),
> dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not
> stripped
Sorry, you're right, using -pie does create an ET_DYN file. So I
suppose that technically it is a shared library.
>> > This can read arguments fine, but dlsym() fails:
>> >
>> > ./library.so: undefined symbol: my_func
>>
>> You can probably fix that problem by linking with -rdynamic.
>
> Didn't work, unfortunately, same problem.
Worked fine when I tried it. I built your source code using
gcc -fPIE -pie -o foo.so foo.c -rdynamic
Then I created this file:
#include <dlfcn.h>
#include <stdlib.h>
#include <stdio.h>
void
die (const char *msg)
{
fprintf (stderr, "%s: %s\n", msg, dlerror ());
exit (EXIT_FAILURE);
}
int
main()
{
void *handle = dlopen ("./foo.so", RTLD_LAZY);
if (handle == NULL)
die ("dlopen");
void *sym = dlsym (handle, "my_func");
if (sym == NULL)
die ("sym");
void (*pfn)(int) = (void (*)(int)) sym;
(*pfn) (3);
return 0;
}
gcc -o foo2 foo2.c
./foo2
printed
Inside my_func: 3
Ian
