Implement <unwind-link.h> for dynamically loading the libgcc_s unwinder

This will be used to consolidate the libgcc_s access for backtrace
and pthread_cancel.

Unlike the existing backtrace implementations, it provides some
hardening based on pointer mangling.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/sysdeps/i386/unwind-arch.h b/sysdeps/i386/unwind-arch.h
new file mode 100644
index 0000000000..01c74fe814
--- /dev/null
+++ b/sysdeps/i386/unwind-arch.h
@@ -0,0 +1,39 @@
+/* Dynamic loading of the libgcc unwinder.  i386 customization.
+   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/>.  */
+
+#ifndef _ARCH_UNWIND_LINK_H
+#define _ARCH_UNWIND_LINK_H
+
+#define UNWIND_LINK_GETIP 1
+#define UNWIND_LINK_FRAME_STATE_FOR 1
+#define UNWIND_LINK_FRAME_ADJUSTMENT 0
+#define UNWIND_LINK_EXTRA_FIELDS \
+  __typeof (_Unwind_GetGR) *ptr__Unwind_GetGR;
+#define UNWIND_LINK_EXTRA_INIT_SHARED                       \
+  local.ptr__Unwind_GetGR                                   \
+    = __libc_dlsym (local_libgcc_handle, "_Unwind_GetGR");  \
+  assert (local.ptr__Unwind_GetGR != NULL);
+#ifdef PTR_MANGLE
+# define UNWIND_LINK_EXTRA_INIT                 \
+  UNWIND_LINK_EXTRA_INIT_SHARED                 \
+  PTR_MANGLE (local.ptr__Unwind_GetGR);
+#else
+# define UNWIND_LINK_EXTRA_INIT UNWIND_LINK_EXTRA_INIT_SHARED
+#endif
+
+#endif /* _ARCH_UNWIND_LINK_H */