elf: Partially initialize ld.so after static dlopen (bug 20802)

After static dlopen, a copy of ld.so is loaded into the inner
namespace, but that copy is not initialized at all.  Some
architectures run into serious problems as result, which is why the
_dl_var_init mechanism was invented.  With libpthread moving into
libc and parts into ld.so, more architectures impacted, so it makes
sense to switch to a generic mechanism which performs the partial
initialization.

As a result, getauxval now works after static dlopen (bug 20802).

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/elf/rtld_static_init.c b/elf/rtld_static_init.c
new file mode 100644
index 0000000..cd82309
--- /dev/null
+++ b/elf/rtld_static_init.c
@@ -0,0 +1,56 @@
+/* Partial initialization of ld.so loaded via static dlopen.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <assert.h>
+
+/* Very special case: This object is built into the static libc, but
+   must know the layout of _rtld_global_ro.  */
+#define SHARED
+#include <ldsodefs.h>
+
+#include <rtld_static_init.h>
+
+void
+__rtld_static_init (struct link_map *map)
+{
+  const ElfW(Sym) *sym
+    = _dl_lookup_direct (map, "_rtld_global_ro",
+                         0x9f28436a, /* dl_new_hash output.  */
+                         "GLIBC_PRIVATE",
+                         0x0963cf85); /* _dl_elf_hash output.  */
+  assert (sym != NULL);
+  struct rtld_global_ro *dl = DL_SYMBOL_ADDRESS (map, sym);
+
+  /* Perform partial initialization here.  Note that this runs before
+     ld.so is relocated, so only members initialized without
+     relocations can be written here.  */
+#ifdef HAVE_AUX_VECTOR
+  extern __typeof (dl->_dl_auxv) _dl_auxv attribute_hidden;
+  dl->_dl_auxv = _dl_auxv;
+  extern __typeof (dl->_dl_clktck) _dl_clktck attribute_hidden;
+  dl->_dl_clktck = _dl_clktck;
+#endif
+  extern __typeof (dl->_dl_hwcap) _dl_hwcap attribute_hidden;
+  dl->_dl_hwcap = _dl_hwcap;
+  extern __typeof (dl->_dl_hwcap2) _dl_hwcap2 attribute_hidden;
+  dl->_dl_hwcap2 = _dl_hwcap2;
+  extern __typeof (dl->_dl_pagesize) _dl_pagesize attribute_hidden;
+  dl->_dl_pagesize = _dl_pagesize;
+
+  __rtld_static_init_arch (map, dl);
+}