[v2,0/9] ld: Implement DT_RELR for x86

  Hi Nick,

I'd like to enable DT_RELR for x86 in binutils 2.38.


H.J.
---
Changes in v2:

1. Drop the _bfd_elf_link_iterate_on_relocs patch, which has been checked
into master branch.
2. Also pack R_*_RELATIVE relocations against dynamic symbols.
3. Skip relocation against IFUNC symbol earlier.
4. Don't require the --relax option enabled.
5. Add more DT_RELR tests:
   a. Add a test with relative relocation in section with 1-byte
      alignment.
   b. Add a test with -z pack-relative-relocs --no-relax.
   c. Add tests for packing R_*_RELATIVE relocations against dynamic
      symbols.

DT_RELR encodes consecutive R_*_RELATIVE relocations in GOT (the global
offset table) and data sections in a compact format:

https://groups.google.com/g/generic-abi/c/bX460iggiKg

On some targets, R_*_RELATIVE relocations are counted and the GOT offsets
are allocated when setting the dynamic section sizes after seeing all
relocations.  R_*_RELATIVE relocations are generated while relocating
sections after section layout has been finalized.

For x86 targets, the old check_relocs is renamed to scan_relocs and a
new check_relocs is added to chek input sections and create dynamic
relocation sections so that they will be mapped to output sections.
scan_relocs is now called from elf_backend_always_size_sections.

On some targets, the DT_RELR section size can be computed only after all
symbols addresses can be determined:

1. Update ldelf_map_segments to pass need_layout to
_bfd_elf_map_sections_to_segments which will size DT_RELR section and
set need_layout to true if the DT_RELR section size is changed.
2.  Set the preliminary DT_RELR section size before mapping sections to
segments and set the final DT_RELR section size after regular symbol
processing is done.

On x86, DT_RELR is implemented with linker relaxation:

1. During linker relaxation, we scan input relocations with the same
logic in relocate_section to determine if a relative relocation should
be generated and save the relative relocation candidate information for
sizing the DT_RELR section later after all symbols addresses can be
determined.  For these relative relocations which can't be placed in
the DT_RELR section, they will be placed in the rela.dyn/rel.dyn
section.
2. When DT_RELR is enabled, _bfd_elf_map_sections_to_segments calls a
backend function to size the DT_RELR section which will compute the
DT_RELR section size and tell ldelf_map_segments to layout sections
again when the DT_RELR section size has been increased.
3. After regular symbol processing is finished, bfd_elf_final_link calls
a backend function to finish the DT_RELR section.

When DT_RELR is enabled, to avoid random run-time crash with older glibc
binaries without DT_RELR support, add a GLIBC_ABI_DT_RELR symbol version,
which is provided by glibc with DT_RELR support, dependency on the shared
C library if it provides a GLIBC_2.XX symbol version.

It can build DT_RELR enabled glibc successfully on x86-64, x32 and
i686.

H.J. Lu (9):
  elf: Add .relr.dyn to special_sections_r
  elf: Extract _bfd_elf_process_reverse_copy
  elf: Pass need_layout to _bfd_elf_map_sections_to_segments
  ld: Initial DT_RELR support
  elf: Add size_relative_relocs and finish_relative_relocs
  elf: Support DT_RELR in linker tests
  x86: Add DT_RELR support
  ld: Add simple DT_RELR tests
  ld: Add glibc dependency for DT_RELR

 bfd/elf-bfd.h                                 |  15 +-
 bfd/elf.c                                     |  22 +-
 bfd/elf32-i386.c                              |  77 +-
 bfd/elf64-x86-64.c                            |  92 +-
 bfd/elflink.c                                 | 168 ++-
 bfd/elfxx-target.h                            |   8 +
 bfd/elfxx-x86.c                               | 954 ++++++++++++++++++
 bfd/elfxx-x86.h                               | 147 ++-
 binutils/testsuite/lib/binutils-common.exp    |   1 +
 include/bfdlink.h                             |   4 +
 ld/NEWS                                       |   3 +
 ld/emulparams/dt-relr.sh                      |  21 +
 ld/emulparams/elf32_x86_64.sh                 |   1 +
 ld/emulparams/elf_i386.sh                     |   1 +
 ld/emulparams/elf_x86_64.sh                   |   1 +
 ld/emultempl/elf.em                           |   5 +-
 ld/ld.texi                                    |  13 +
 ld/ldelf.c                                    |   9 +
 ld/ldelfgen.c                                 |   3 +-
 ld/ldlang.c                                   |   3 +-
 ld/scripttempl/elf.sc                         |   4 +
 ld/testsuite/config/default.exp               |  16 +
 ld/testsuite/ld-elf/dt-relr-1.s               |  13 +
 ld/testsuite/ld-elf/dt-relr-1a.d              |  10 +
 ld/testsuite/ld-elf/dt-relr-1b.d              |   9 +
 ld/testsuite/ld-elf/dt-relr-1c.d              |   9 +
 ld/testsuite/ld-elf/dt-relr-2.s               |  20 +
 ld/testsuite/ld-elf/dt-relr-2a.d              |  10 +
 ld/testsuite/ld-elf/dt-relr-2b.d              |  17 +
 ld/testsuite/ld-elf/dt-relr-2c.d              |  17 +
 ld/testsuite/ld-elf/dt-relr-2d.d              |  17 +
 ld/testsuite/ld-elf/dt-relr-2e.d              |   9 +
 ld/testsuite/ld-elf/dt-relr-2f.d              |   8 +
 ld/testsuite/ld-elf/dt-relr-2g.d              |   9 +
 ld/testsuite/ld-elf/dt-relr-2h.d              |   9 +
 ld/testsuite/ld-elf/dt-relr-3.s               |  12 +
 ld/testsuite/ld-elf/dt-relr-3a.d              |   9 +
 ld/testsuite/ld-elf/dt-relr-3b.d              |   9 +
 ld/testsuite/ld-elf/dt-relr-glibc-1.c         |  11 +
 ld/testsuite/ld-elf/dt-relr-glibc-1a.rd       |   4 +
 ld/testsuite/ld-elf/dt-relr-glibc-1b.rd       |   7 +
 ld/testsuite/ld-elf/dt-relr.exp               |  44 +
 ld/testsuite/ld-elf/shared.exp                |   3 +-
 ld/testsuite/ld-i386/dt-relr-1.d              |  14 +
 ld/testsuite/ld-i386/dt-relr-1.s              |   3 +
 ld/testsuite/ld-i386/export-class.exp         |   2 +-
 ld/testsuite/ld-i386/i386.exp                 |  21 +-
 ld/testsuite/ld-i386/ibt-plt-2a.d             |   2 +-
 ld/testsuite/ld-i386/ibt-plt-3a.d             |   2 +-
 ld/testsuite/ld-i386/ibt-plt-3c.d             |   2 +-
 ld/testsuite/ld-i386/pr26869.d                |   2 +-
 ld/testsuite/ld-i386/report-reloc-1.d         |   2 +-
 ld/testsuite/ld-ifunc/ifunc-2-i386-now.d      |   2 +-
 .../ld-ifunc/ifunc-2-local-i386-now.d         |   2 +-
 .../ld-ifunc/ifunc-2-local-x86-64-now.d       |   2 +-
 ld/testsuite/ld-ifunc/ifunc-2-x86-64-now.d    |   2 +-
 ld/testsuite/ld-ifunc/pr17154-x86-64-now.d    |   2 +-
 ld/testsuite/ld-ifunc/pr17154-x86-64.d        |   2 +-
 ld/testsuite/ld-x86-64/bnd-branch-1-now.d     |   2 +-
 ld/testsuite/ld-x86-64/bnd-ifunc-1-now.d      |   2 +-
 ld/testsuite/ld-x86-64/bnd-ifunc-2-now.d      |   2 +-
 ld/testsuite/ld-x86-64/bnd-ifunc-2.d          |   2 +-
 ld/testsuite/ld-x86-64/bnd-plt-1-now.d        |   2 +-
 ld/testsuite/ld-x86-64/bnd-plt-1.d            |   2 +-
 ld/testsuite/ld-x86-64/dt-relr-1-x32.d        |  15 +
 ld/testsuite/ld-x86-64/dt-relr-1.d            |  14 +
 ld/testsuite/ld-x86-64/dt-relr-1.s            |   3 +
 ld/testsuite/ld-x86-64/export-class.exp       |   3 +-
 ld/testsuite/ld-x86-64/ibt-plt-2a-x32.d       |   2 +-
 ld/testsuite/ld-x86-64/ibt-plt-2a.d           |   2 +-
 ld/testsuite/ld-x86-64/ibt-plt-3a-x32.d       |   2 +-
 ld/testsuite/ld-x86-64/ibt-plt-3a.d           |   2 +-
 ld/testsuite/ld-x86-64/ilp32-4.d              |   2 +-
 ld/testsuite/ld-x86-64/load1c.d               |   2 +-
 ld/testsuite/ld-x86-64/load1d.d               |   2 +-
 ld/testsuite/ld-x86-64/pr13082-2b.d           |   2 +-
 ld/testsuite/ld-x86-64/pr14207.d              |   2 +-
 ld/testsuite/ld-x86-64/pr18176.d              |   2 +-
 ld/testsuite/ld-x86-64/pr19162.d              |   2 +-
 ld/testsuite/ld-x86-64/pr19636-2d.d           |   2 +-
 ld/testsuite/ld-x86-64/pr19636-2l.d           |   2 +-
 ld/testsuite/ld-x86-64/pr20253-1d.d           |   2 +-
 ld/testsuite/ld-x86-64/pr20253-1f.d           |   2 +-
 ld/testsuite/ld-x86-64/pr20253-1j.d           |   2 +-
 ld/testsuite/ld-x86-64/pr20253-1l.d           |   2 +-
 ld/testsuite/ld-x86-64/report-reloc-1-x32.d   |   2 +-
 ld/testsuite/ld-x86-64/report-reloc-1.d       |   2 +-
 ld/testsuite/ld-x86-64/x86-64.exp             |  67 +-
 88 files changed, 1883 insertions(+), 155 deletions(-)
 create mode 100644 ld/emulparams/dt-relr.sh
 create mode 100644 ld/testsuite/ld-elf/dt-relr-1.s
 create mode 100644 ld/testsuite/ld-elf/dt-relr-1a.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-1b.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-1c.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2.s
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2a.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2b.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2c.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2d.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2e.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2f.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2g.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-2h.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-3.s
 create mode 100644 ld/testsuite/ld-elf/dt-relr-3a.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-3b.d
 create mode 100644 ld/testsuite/ld-elf/dt-relr-glibc-1.c
 create mode 100644 ld/testsuite/ld-elf/dt-relr-glibc-1a.rd
 create mode 100644 ld/testsuite/ld-elf/dt-relr-glibc-1b.rd
 create mode 100644 ld/testsuite/ld-elf/dt-relr.exp
 create mode 100644 ld/testsuite/ld-i386/dt-relr-1.d
 create mode 100644 ld/testsuite/ld-i386/dt-relr-1.s
 create mode 100644 ld/testsuite/ld-x86-64/dt-relr-1-x32.d
 create mode 100644 ld/testsuite/ld-x86-64/dt-relr-1.d
 create mode 100644 ld/testsuite/ld-x86-64/dt-relr-1.s