mbox

[0/7] Support DT_RELR relative relocation format

Message ID 20220203180948.2744-1-hjl.tools@gmail.com
Headers

Message

H.J. Lu Feb. 3, 2022, 6:09 p.m. UTC 
  PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.

Binutils 2.38 supports DT_RELR on x86 with the -z report-relative-reloc
option.  When DT_RELR is enabled, ld adds a GLIBC_ABI_DT_RELR symbol
version dependency on libc.so to outputs.  The DT_RELR support is enabled
in ld.so only if the linker supports -z report-relative-reloc option.

DT_RELR is enabled in glibc shared libraries and position independent
executables (PIE) automatically if linker supports -z pack-relative-relocs
nd the architecture defines SUPPORT_DT_RELR in config.h.  At the moment,
only x86 targets define SUPPORT_DT_RELR.

The DT_RELR usage in glibc can be disabled with --disable-default-dt-relr.

Tested with binutils 2.38 on i686, x86-64 and x32.

Fangrui Song (1):
  elf: Support DT_RELR relative relocation format [BZ #27924]

H.J. Lu (6):
  elf: Properly handle zero DT_RELA/DT_REL values
  Add GLIBC_ABI_DT_RELR for DT_RELR support
  x86/configure.ac: Define PI_STATIC_AND_HIDDEN/SUPPORT_STATIC_PIE
  x86: Define SUPPORT_DT_RELR
  Add --disable-default-dt-relr
  NEWS: Mention DT_RELR support

 INSTALL                     |  6 +++
 Makeconfig                  | 19 +++++++++
 Makerules                   |  2 +
 NEWS                        |  5 +++
 config.h.in                 |  6 +++
 configure                   | 84 +++++++++++++++++++++++++++++++++++++
 configure.ac                | 34 +++++++++++++++
 elf/Makefile                | 36 ++++++++++++++--
 elf/Versions                |  7 ++++
 elf/dynamic-link.h          | 40 +++++++++++++++++-
 elf/elf.h                   | 13 +++++-
 elf/get-dynamic-info.h      | 19 +++++++--
 elf/libc-abi-version.exp    |  1 +
 elf/tst-relr-pie.c          |  1 +
 elf/tst-relr.c              | 64 ++++++++++++++++++++++++++++
 manual/install.texi         |  5 +++
 scripts/abilist.awk         |  2 +
 scripts/versions.awk        |  7 +++-
 sysdeps/i386/configure      |  6 ---
 sysdeps/i386/configure.ac   |  7 ----
 sysdeps/x86/configure       |  9 ++++
 sysdeps/x86/configure.ac    | 10 +++++
 sysdeps/x86_64/configure    |  6 ---
 sysdeps/x86_64/configure.ac |  7 ----
 24 files changed, 360 insertions(+), 36 deletions(-)
 create mode 100644 elf/libc-abi-version.exp
 create mode 100644 elf/tst-relr-pie.c
 create mode 100644 elf/tst-relr.c