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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.
13 lines
382 B
Plaintext
13 lines
382 B
Plaintext
tmpdir/gotreloc_64-1: file format elf64-s390
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Disassembly of section .text:
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.* <foo>:
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.*: c0 10 00 00 00 0e [ ]*larl %r1,.* <bar>
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.*: c0 10 00 00 00 0b [ ]*larl %r1,.* <bar>
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.*: c4 1d 00 00 0f 1a [ ]*lrl %r1,.* <_GLOBAL_OFFSET_TABLE_\+0x18>
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.*: 58 10 c0 18 [ ]*l %r1,24\(%r12\)
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.*: e3 10 c0 18 00 58 [ ]*ly %r1,24\(%r12\)
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.* <bar>:
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.*: 00 00 01 23 .long 0x00000123
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