elf: Move vDSO setup to rtld (BZ#24967)

This patch moves the vDSO setup from libc to loader code, just after
the vDSO link_map setup.  For static case the initialization
is moved to _dl_non_dynamic_init instead.

Instead of using the mangled pointer, the vDSO data is set as
attribute_relro (on _rtld_global_ro for shared or _dl_vdso_* for
static).  It is read-only even with partial relro.

It fixes BZ#24967 now that the vDSO pointer is setup earlier than
malloc interposition is called.

Also, vDSO calls should not be a problem for static dlopen as
indicated by BZ#20802.  The vDSO pointer would be zero-initialized
and the syscall will be issued instead.

Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
arm-linux-gnueabihf, powerpc64le-linux-gnu, powerpc64-linux-gnu,
powerpc-linux-gnu, s390x-linux-gnu, sparc64-linux-gnu, and
sparcv9-linux-gnu.  I also run some tests on mips.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

elf/dl-support.c

@@ -34,6 +34,8 @@
 #include <unsecvars.h>
 #include <hp-timing.h>
 #include <stackinfo.h>
+#include <dl-vdso.h>
+#include <dl-vdso-setup.h>
 
 extern char *__progname;
 char **_dl_argv = &__progname;	/* This is checked for some error messages.  */
@@ -201,6 +203,8 @@ struct link_map *_dl_sysinfo_map;
 # include "get-dynamic-info.h"
 #endif
 #include "setup-vdso.h"
+/* Define the vDSO function pointers.  */
+#include <dl-vdso-setup.c>
 
 /* During the program run we must not modify the global data of
    loaded shared object simultanously in two threads.  Therefore we
@@ -315,6 +319,9 @@ _dl_non_dynamic_init (void)
      so they can influence _dl_init_paths.  */
   setup_vdso (NULL, NULL);
 
+  /* With vDSO setup we can initialize the function pointers.  */
+  setup_vdso_pointers ();
+
   /* Initialize the data structures for the search paths for shared
      objects.  */
   _dl_init_paths (getenv ("LD_LIBRARY_PATH"));