/*
* Protect against dlsym interception.
*
* We implement the whole API, so we don't need to intercept dlsym -- dlopen is
* enough. However we need to protect against other dynamic libraries
* intercepting dlsym, to prevent infinite recursion,
*
* In particular the Steam Community Overlay exports dlsym. See also
* http://lists.freedesktop.org/archives/apitrace/2013-March/000573.html
*/
PRIVATE
void *
dlsym(void * handle, const char * symbol)
{
/*
* We rely on glibc's internal __libc_dlsym. See also
* http://www.linuxforu.com/2011/08/lets-hook-a-library-function/
*
* Use use it to obtain the true dlsym. We don't use __libc_dlsym directly
* because it does not support things such as RTLD_NEXT.
*/
typedef void * (*PFN_DLSYM)(void *, const char *);
static PFN_DLSYM dlsym_ptr = NULL;
if (!dlsym_ptr) {
void *libdl_handle = __libc_dlopen_mode("libdl.so.2", RTLD_LOCAL | RTLD_NOW);
if (libdl_handle) {
dlsym_ptr = (PFN_DLSYM)__libc_dlsym(libdl_handle, "dlsym");
}
if (!dlsym_ptr) {
os::log("apitrace: error: failed to look up real dlsym\n");
return NULL;
}
}
return dlsym_ptr(handle, symbol);
}
int main(int argc, char **argv) {
void *handle;
double (*puts)(char *);
char *error;
handle = __libc_dlopen_mode("libc.so.6", RTLD_LAZY);
if (!handle) {
exit(1);
}
puts = __libc_dlsym(handle, "puts");
(*puts)("Hello World");
__libc_dlclose(handle);
}
void * threadfunc (void * arg)
{
printf ("in threadfunc\n");
void * handle = __libc_dlopen_mode ("./test_unload.so", RTLD_LAZY | 0x80000000);
printf ("dlopen ok handle: %p\n", handle);
void (*pfn_shared_method)(void) = __libc_dlsym(handle, "shared_method");
printf ("before func\n");
pfn_shared_method ();
printf ("after func\n");
printf ("about to dlclose handle: %p\n", handle);
__libc_dlclose (handle);
printf ("done dlclose\n");
while (!stopping)
sleep (1);
printf ("leaving threadfunc\n");
stopped = 1;
}
static void
gum_libdl_prevent_unload (void)
{
__libc_dlopen_mode ("libdl.so.2", RTLD_LAZY | GUM_RTLD_DLOPEN);
}
static void load_library(const char* filename)
{
// Yay! Using internals of libc! Let's just cross fingers this won't change too fast :/
void* (*__libc_dlopen_mode)(const char*, int) = resolve_symbol("libc.so.6", "__libc_dlopen_mode");
__libc_dlopen_mode(filename, RTLD_NOW | RTLD_GLOBAL);
}
