This might be what you're looking for, if I understood you correctly. I'll be using libpthread as the hypothetical dylib containing functions you want to re-export.
mybundle.c:
#include <pthread.h>
#include <stdio.h>
void *foo(void *ctx) {
puts((char *)ctx);
return 0;
}
mybundle.exp:
_foo
_pthread_create
_pthread_join
Compile the bundle, dynamically linking to libpthread.dylib:
josh$ gcc -bundle -lpthread -Wl,-exported_symbols_list,mybundle.exp -o mybundle.so mybundle.c
myloader.c:
#include <dlfcn.h>
#include <pthread.h> // merely for type definitions
#include <assert.h>
#include <stdio.h>
int main() {
void *(*foo)(void *ctx);
/* the following cannot be declared globally without changing their names,
as they are already (and unnecessarily) declared in <pthread.h> */
int (*pthread_create)(pthread_t *thrd, const pthread_attr_t *attr, void *(*proc)(void *), void *arg);
int (*pthread_join)(pthread_t thrd, void **val);
void *bundle;
assert(bundle = dlopen("mybundle.so", RTLD_NOW));
assert(foo = dlsym(bundle, "foo"));
assert(pthread_create = dlsym(bundle, "pthread_create"));
assert(pthread_join = dlsym(bundle, "pthread_join"));
pthread_t myThrd;
pthread_create(&myThrd, 0, foo, "in another thread");
pthread_join(myThrd, 0);
return 0;
}
Compile the loader:
josh$ gcc myloader.c -o myloader
Run:
josh$ ./myloader
in another thread
Observe that myloader is in no way linked to pthread, yet pthread functions are loaded and available at runtime through the bundle.