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>

2 files changed, 31 insertions, 0 deletions

diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 8426b5cbd8..e43d6f5ecd 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1313,6 +1313,13 @@ dl_init_static_tls (struct link_map *map)
 #endif
 }
 
+#ifndef SHARED
+/* Called before relocating ld.so during static dlopen.  This can be
+   used to partly initialize the dormant ld.so copy in the static
+   dlopen namespace.  */
+void __rtld_static_init (struct link_map *map) attribute_hidden;
+#endif
+
 /* Return true if the ld.so copy in this namespace is actually active
    and working.  If false, the dl_open/dlfcn hooks have to be used to
    call into the outer dynamic linker (which happens after static
diff --git a/sysdeps/generic/rtld_static_init.h b/sysdeps/generic/rtld_static_init.h
new file mode 100644
index 0000000000..3f8dde22a8
--- /dev/null
+++ b/sysdeps/generic/rtld_static_init.h
@@ -0,0 +1,24 @@
+/* Partial initialization of ld.so loaded via static dlopen.  Generic helper.
+   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/>.  */
+
+static inline void
+__rtld_static_init_arch (struct link_map *map, struct rtld_global_ro *dl)
+{
+  /* The generic helper does not perform any additional
+     initialization.  */
+}