Message ID | 20220303045026.4172347-1-hjl.tools@gmail.com |
---|---|
Headers | show |
Series | Support DT_RELR relative relocation format | expand |
On 2022-03-02, H.J. Lu wrote: >Changes in v5: > >1. Update NEWS entry with the linker option, -z pack-relative-relocs. >2. Remove elf/libc-abi-version.exp and use $(READELF) to check >GLIBC_ABI_DT_RELR. > >Changes in v4: > >1. Always enable GLIBC_ABI_DT_RELR check. >2. Use $(OBJDUMP) instead of $(NM) for GLIBC_ABI_DT_RELR check. > >Changes in v3: > >1. Don't define SUPPORT_DT_RELR. >2. Enable DT_RELR in glibc shared libraries and position independent >executables (PIE) automatically if linker supports -z pack-relative-relocs. > >Changes in v2: > >1. Enable DT_RELR for all targets. >2. Issue an error if there is a DT_RELR entry without GLIBC_ABI_DT_RELR >dependency nor GLIBC_PRIVATE definition. > >--- >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. Issue an error if there is a >DT_RELR entry without GLIBC_ABI_DT_RELR dependency nor GLIBC_PRIVATE >definition. > >DT_RELR is enabled in glibc shared libraries and position independent >executables (PIE) automatically if linker supports -z pack-relative-relocs. > >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 (4): > elf: Properly handle zero DT_RELA/DT_REL values > Add GLIBC_ABI_DT_RELR for DT_RELR support > Add --disable-default-dt-relr > NEWS: Mention DT_RELR support > > INSTALL | 6 ++++ > Makeconfig | 19 +++++++++++++ > Makerules | 2 ++ > NEWS | 3 +- > configure | 60 +++++++++++++++++++++++++++++++++++++++ > configure.ac | 23 +++++++++++++++ > elf/Makefile | 30 ++++++++++++++++++-- > elf/Versions | 5 ++++ > elf/dl-version.c | 33 ++++++++++++++++++++-- > elf/dynamic-link.h | 40 +++++++++++++++++++++++++- > elf/elf.h | 13 +++++++-- > elf/get-dynamic-info.h | 19 +++++++++++-- > elf/tst-relr-pie.c | 1 + > elf/tst-relr.c | 64 ++++++++++++++++++++++++++++++++++++++++++ > include/link.h | 6 ++++ > manual/install.texi | 5 ++++ > scripts/abilist.awk | 2 ++ > scripts/versions.awk | 7 ++++- > 18 files changed, 325 insertions(+), 13 deletions(-) > create mode 100644 elf/tst-relr-pie.c > create mode 100644 elf/tst-relr.c > >-- >2.35.1 > Thanks! And thanks for adjusting the objdump/readelf tests to make lld happy. Reviewed-by: Fangrui Song <maskray@google.com> Would be good to check with Joseph, who had some opinions with v1. I have a new lld with https://reviews.llvm.org/D120701 and have checked that the patch series with (/usr/local/bin/ld == my new lld) works. * regular PIE with .relr.dyn work. * static PIE with .relr.dyn work. I echo what Peter mentioned in https://sourceware.org/pipermail/libc-alpha/2022-March/136773.html See also Gentoo Linux's feedback in a similar line https://sourceware.org/pipermail/libc-alpha/2021-November/133388.html I do believe for many distributions this is not so necessary and gives linkers busywork. But if this version lockout mechanism is the deal breaker for glibc to have DT_RELR at all, I am fine with it, for users' good.