ld.so: Replace DL_RO_DYN_SECTION with dl_relocate_ld [BZ #28340]

We can't relocate entries in dynamic section if it is readonly:

1. Add a l_ld_readonly field to struct link_map to indicate if dynamic
section is readonly and set it based on p_flags of PT_DYNAMIC segment.
2. Replace DL_RO_DYN_SECTION with dl_relocate_ld to decide if dynamic
section should be relocated.
3. Remove DL_RO_DYN_TEMP_CNT.
4. Don't use a static dynamic section to make readonly dynamic section
in vDSO writable.
5. Remove the temp argument from elf_get_dynamic_info.

This fixes BZ #28340.

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

2 files changed, 32 insertions, 4 deletions

diff --git a/sysdeps/mips/dl-relocate-ld.h b/sysdeps/mips/dl-relocate-ld.h
new file mode 100644
index 0000000000..0c18d9a567
--- /dev/null
+++ b/sysdeps/mips/dl-relocate-ld.h
@@ -0,0 +1,32 @@
+/* Check if dynamic section should be relocated.  MIPS version.
+   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 _DL_RELOCATE_LD_H
+#define _DL_RELOCATE_LD_H
+
+/* Return true if dynamic section in the shared library L should be
+   relocated.  */
+
+static inline bool
+dl_relocate_ld (const struct link_map *l)
+{
+  /* Never relocate dynamic section.  */
+  return false;
+}
+
+#endif /* _DL_RELOCATE_LD_H */
diff --git a/sysdeps/mips/ldsodefs.h b/sysdeps/mips/ldsodefs.h
index 4db7c60e38..36fd09a8bd 100644
--- a/sysdeps/mips/ldsodefs.h
+++ b/sysdeps/mips/ldsodefs.h
@@ -75,10 +75,6 @@ struct La_mips_64_retval;
 					  struct La_mips_64_retval *,	    \
 					  const char *);
 
-/* The MIPS ABI specifies that the dynamic section has to be read-only.  */
-
-#define DL_RO_DYN_SECTION 1
-
 #include_next <ldsodefs.h>
 
 /* The 64-bit MIPS ELF ABI uses an unusual reloc format.  Each