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From: "Fāng-ruì Sòng" <maskray@google.com>
To: "Carlos O'Donell" <carlos@redhat.com>
Cc: libc-alpha@sourceware.org, binutils@sourceware.org
Subject: Re: [PATCH v2] elf: Support DT_RELR relative relocation format [BZ #27924]
Date: Fri, 29 Oct 2021 11:38:01 -0700	[thread overview]
Message-ID: <CAFP8O3KkiSf0o0mLWGHZUR-aT1awN3L0J2viDx98qzbXTNoNwQ@mail.gmail.com> (raw)
In-Reply-To: <1763c6f4-dfb9-e102-84d6-892ee2a3208a@redhat.com>

On Fri, Oct 29, 2021 at 11:21 AM Carlos O'Donell <carlos@redhat.com> wrote:
>
> On 10/16/21 20:50, Fangrui Song via Binutils wrote:
> > 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.
>
> We've been going over this patch on the weekly Monday patch queue review.
>
> I took a note to point out that one of the blockers here is that it is difficult
> to immediately test this work because it requires a working glibc build using
> ldd (which has support for DT_RELR).

No:) There may be a misunderstanding.

To test the feature: a DT_RELR executable is needed.
Currently only ld.lld --pack-dyn-relocs=relr supports generating
DT_RELR binaries,
but glibc itself does not need to be linked with ld.lld.

If the patch is accepted, GNU ld built glibc will support DT_RELR
programs linked by ld.lld.
ld.lld has supported --pack-dyn-relocs=relr since 2017-12.
ld.lld --pack-dyn-relocs=relr (-pie|-shared) produced output works on
Android, Fuchsia, FreeBSD (https://reviews.freebsd.org/D32524)

You can see that the code here is fully generic, not tightly to a
specific linker.

For my purpose and to Linux distro's interest, I'd definitely want to
see that the glibc patch is accepted even in the lack of GNU ld
support.

> What is the status of the lld support patches for glibc?

aarch64 and x86-64 work well for me.
Seems that Adhemerval may be interested in adding a lld configuration
to scripts/build-many-glibcs.py

> If we made progress on the lld support then we'd be able to more easily review
> a testable configuration and keep the review going forward.
>
> --
> Cheers,
> Carlos.
>

  parent reply	other threads:[~2021-10-29 18:38 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-17  0:50 Fangrui Song
2021-10-18 14:42 ` H.J. Lu
2021-10-18 16:16   ` Fāng-ruì Sòng
2021-10-18 17:28     ` H.J. Lu
2021-10-18 18:15       ` Fāng-ruì Sòng
2021-10-18 18:27         ` H.J. Lu
2021-10-18 19:19           ` Fāng-ruì Sòng
2021-10-18 19:44             ` H.J. Lu
2021-10-18 20:11               ` Fāng-ruì Sòng
2021-10-18 21:10                 ` Joseph Myers
2021-10-18 22:27                   ` H.J. Lu
2021-10-18 22:30                     ` Joseph Myers
2021-10-18 22:42                       ` H.J. Lu
2021-10-18 23:00                         ` Joseph Myers
2021-10-18 23:36                           ` H.J. Lu
2021-10-18 23:44                             ` Joseph Myers
2021-10-19  1:05                               ` H.J. Lu
2021-10-18 19:21       ` Joseph Myers
2021-10-18 19:45         ` H.J. Lu
2021-10-29 18:21 ` Carlos O'Donell
2021-10-29 18:36   ` H.J. Lu
2021-10-29 19:15     ` Fangrui Song
2021-10-29 18:38   ` Fāng-ruì Sòng [this message]
2021-10-29 19:35     ` Carlos O'Donell
2021-10-29 19:53       ` Adhemerval Zanella
2021-11-01  4:50         ` Fāng-ruì Sòng

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