Currently on S/390 the .got.plt always comes first which prevents the
GNU_RELRO segment from being extended across the non-plt GOT entries.
Just swapping both unfortunately is not that simple since our ABI
requires the _GLOBAL_OFFSET_TABLE_ symbol to point to the very
beginning of the entire GOT. Of the 3 magic GOT entries the first is
accessed via got pointer while second and third are being accessed via
DT_PLTGOT. In order to keep them together we make DT_PLTGOT to point
to the .got instead of .got.plt. However, this violates an assumption
in the dynamic linker prelink undo code about the GOTPLT entries
starting at DT_PLTGOT + 3. We got rid of this requirement with a
Glibc patch already in version 2.24:
https://sourceware.org/ml/libc-alpha/2016-06/msg01302.html
So the S/390 relro GOT layout will look like this with this patch:
+----------------------------------+
|got[0]: DYNAMIC | <--- _GLOBAL_OFFSET_TABLE_ == DT_PLTGOT .got
|got[1]: link_map parm |
|got[2]: &_dl_runtime_resolve |
+----------------------------------+
| | non-plt GOT entries
| |
| |
+----------------------------------+
| | <--- .gotplt, PLT GOT entries
| |
| |
| |
+----------------------------------+
The patch detects the current layout in size_dynamic_section in order
to deal also with linker scripts not generated by this ld version.
With partial relro enabled we pick a linker script where .got and
.got.plt are swapped which then triggers the rest of the logic.
ld/ChangeLog:
2018-07-18 Andreas Krebbel <krebbel@linux.ibm.com>
* emulparams/elf64_s390.sh: Define GENERATE_RELRO_SCRIPT and
SEPARATE_GOTPLT.
* testsuite/ld-s390/gotreloc_64-relro-1.dd: New test.
* testsuite/ld-s390/gotreloc_64-norelro-1.dd: Renamed from ...
* testsuite/ld-s390/gotreloc_64-1.dd: ... this.
* testsuite/ld-s390/s390.exp: Split the GOT testcase into two.
bfd/ChangeLog:
2018-07-18 Andreas Krebbel <krebbel@linux.ibm.com>
* elf-s390-common.c (s390_gotplt_after_got_p): New function.
(s390_got_pointer): New function.
(s390_got_offset): New function.
(s390_gotplt_offset): New function.
* elf64-s390.c (allocate_dynrelocs): Adjust comment.
(elf_s390_size_dynamic_sections): Move space for magic GOT entries
from .got.plt to .got if necessary and pick the right location for
_GLOBAL_OFFSET_TABLE_.
(elf_s390_relocate_section): Use the wrapper functions from
elf-s390-common.c to deal with both possible layouts (either .got
or .got.plt first).
(elf_s390_finish_dynamic_sections): Likewise.
(elf_s390_finish_dynamic_symbol): Make the location of the GOT
magic entries conditional.
afca762f59