libtsan invalid use of ld-linux internals

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

I've noticed libtsan can't be installed via rpm, due to invalid use of
dynamic linker's internals:

#ifdef __i386__
# define INTERNAL_FUNCTION __attribute__((regparm(3), stdcall))
#else
# define INTERNAL_FUNCTION
#endif
extern "C" void _dl_get_tls_static_info(size_t*, size_t*)
    __attribute__((weak)) INTERNAL_FUNCTION;

static int InitTlsSize() {
  typedef void (*get_tls_func)(size_t*, size_t*) INTERNAL_FUNCTION;
  get_tls_func get_tls = &_dl_get_tls_static_info;
  if (get_tls == 0) {
    void *get_tls_static_info_ptr = dlsym(RTLD_NEXT, "_dl_get_tls_static_info");
    CHECK_EQ(sizeof(get_tls), sizeof(get_tls_static_info_ptr));
    internal_memcpy(&get_tls, &get_tls_static_info_ptr,
                    sizeof(get_tls_static_info_ptr));
  }
  CHECK_NE(get_tls, 0);
  size_t tls_size = 0;
  size_t tls_align = 0;
  get_tls(&tls_size, &tls_align);
  return tls_size;
}

The
get_tls_func get_tls = &_dl_get_tls_static_info;
is what precludes libtsan installation, then libtsan.so refers to
_dl_get_tls_static_info@@GLIBC_PRIVATE
symbol and at least our rpm dependency stuff reject that, because nothing
outside of glibc should ever refer to symbols marked as GLIBC_PRIVATE.
Those are exported solely because they are used by other libraries that are
part of glibc (in this case libc.so.6).
If you need to get at the info it returns, please talk to
libc-alpha@sourceware.org for help.  The first line certainly must go, the
second alternative (dlsym) will not prevent installation, but may break
anytime, glibc doesn't guarantee anything about the ABI of the symbols, it
can be removed any time, can change parameters/return values without
warning.

	Jakub