None of _start, _end and __INIT_ARRAY__ present in library

[guy-adshir]

Hi I'm trying to hook GLES calls on Android 10 for a Unity apk, but calling library (libunity.so) exports none of the 3 required symbols. The rest of the libraries in the apk all export _end. Any ideas? Thanks!

[kubo]

Does the library libunity.so export some symbols? If so, could you use plthook_open_by_address()?

#include <dlfcn.h>
#include <plthook.h>

plthook_t *plthook;

// The following code is same with what plthook_open does on Android except symbol names.
void *handle = dlopen("libunity.so", RTLD_LAZY | RTLD_NOLOAD);
if (handle == NULL) {
    ... error ...
}
void *addr = dlsym(handle, "any_symbol_name_exported_by_libunity_so");
if (addr != NULL) {
    ... error ...
}
int rv = plthook_open_by_address(&plthook, addr);
if (rv != 0) {
    ... error ...
}

[guy-adshir]

Thank you. 'plthook_open_by_address' succeeds, but then 'plthook_replace' fails, with the error: "no such function: glBindBuffer"

So just to be sure I'm on the right page here: I should be calling dlopen/dlsym/plthook_replace on the library where the CALL I want to hook is located, not the library that holds the implememntation of the function (in my case, glBindBuffer). Also, do I need to wait until the PLT entry for glBindBuffer for libunity.so is resolved?

Thanks again.

[kubo]

Also, do I need to wait until the PLT entry for glBindBuffer for libunity.so is resolved?

It depends on whether you use the fourth argument of plthook_replace. I recommend that you don't. See Usage.

[guy-adshir]

Thanks. I did not use the fourth parameter. Are my assumptions above correct?

Thank you so much for your help

[kubo]

Are my assumptions above correct?

No. If your code don't use the parameter, it doesn't depend on whether the PLT entry is resolved or not.

[guy-adshir]

I'll try debugging it further, thanks :)