From: Alan Modra <amodra@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: Fangrui Song <maskray@google.com>,
GNU C Library <libc-alpha@sourceware.org>,
Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Subject: Re: DT_RELR without libc.so dependency
Date: Thu, 14 Apr 2022 14:48:57 +0930 [thread overview]
Message-ID: <YleuwRhyaKDNk+SC@squeak.grove.modra.org> (raw)
In-Reply-To: <CAMe9rOqopqZZKSOVmfeSQS6eO2k5RiU7J6i3PsdkZYcpOA18gw@mail.gmail.com>
On Wed, Apr 13, 2022 at 06:54:17PM -0700, H.J. Lu wrote:
> On Wed, Apr 13, 2022 at 5:34 PM Alan Modra <amodra@gmail.com> wrote:
> >
> > On Fri, Apr 08, 2022 at 05:14:12PM -0700, Fangrui Song wrote:
> > > HJ's DT_RELR patch series has been upgraded to v7
> > > (https://patchwork.sourceware.org/project/glibc/list/?series=8295)
> > >
> > > git-pw series apply 8295
> > > # `Add --disable-default-dt-relr` does not apply cleanly
> > >
> > > If no regressions with default DT_RELR, that will be cool!
> >
> > I did find one error when testing a build of glibc using Ubuntu gcc-8.
> > elf/filter fails with "error while loading shared libraries:
> > .../elf/filtmod1.so: DT_RELR without GLIBC_ABI_DT_RELR dependency".
> >
> > A little analysis shows the problem occurs when filtmod1.so is linked
> > with --as-needed and libc.so is not needed. filtmod1.so ends up with
> > no .gnu.version or .gnu.version_r sections, and of course no
> > GLIBC_ABI_DT_RELR version.
> >
> > The error check is not one that belongs in ld.so. If you have the
> > error checking code, then you have DT_RELR support in ld.so and there
> > is no reason at all to refuse to run the program! The check should be
> > in the linker, if anywhere.
> >
>
> The GLIBC_ABI_DT_RELR dependency is added to avoid the random
> crush at run-time with older glibc binaries. Since it is possible to create
> a DSO with DT_RELR, but without the libc.so dependency. Should ld.so
> skip the GLIBC_ABI_DT_RELR check if the DSO doesn't depend on
> libc.so?
I understand why you want a dependency, but I do not see a hard
requirement for l_abi_version or any code using it. If you try to run
a new binary with DT_RELR using an old glibc or even current glibc
without relr support, you'll get "version `GLIBC_ABI_DT_RELR' not
found". That is sufficient, presuming there is a GLIBC_ABI_DT_RELR
version in the binary. If there *isn't* a GLIBC_ABI_DT_RELR version
then running that binary on an older glibc probably will crash.
Putting a check in a newer ld.so doesn't help much with that, except
show up this case where the dependency isn't there. I guess the check
is justifiable under some DL_DEBUG flag.
Lack of a dependency is either a linker bug or a relr design bug.
Nitpick: isn't the actual dependency on ld.so rather than libc.so?
--
Alan Modra
Australia Development Lab, IBM
next prev parent reply other threads:[~2022-04-14 5:19 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-23 12:42 [PowerPC64] Use medium model toc accesses throughout Alan Modra
2022-01-24 3:47 ` [PATCH 2/5] [PowerPC64] Set up thread register for _dl_relocate_static_pie Alan Modra
2022-02-16 23:02 ` Paul E Murphy
2022-02-19 0:49 ` Alan Modra
2022-01-24 3:50 ` [PATCH 3/5] [PowerPC] Relocate stinfo->main Alan Modra
2022-01-24 4:48 ` H.J. Lu
2022-01-24 6:51 ` Alan Modra
2022-01-24 3:52 ` [PATCH 4/5] Constify a variable in dl_vdso_vsym Alan Modra
2022-01-24 4:06 ` [PATCH 5/5] Enable static-pie on powerpc64 Alan Modra
2022-01-27 18:39 ` Florian Weimer
2022-01-28 8:45 ` Alan Modra
2022-01-28 17:48 ` [PowerPC64] Use medium model toc accesses throughout Paul E Murphy
2022-01-29 1:24 ` Alan Modra
2022-02-28 6:40 ` [PATCH v2 0/4] PowerPC64 static-pie Alan Modra
2022-02-28 6:40 ` [PATCH v2 1/4] powerpc64: Use medium model toc accesses throughout Alan Modra
2022-04-08 22:28 ` Tulio Magno Quites Machado Filho
2022-02-28 6:40 ` [PATCH v2 2/4] powerpc64: Set up thread register for _dl_relocate_static_pie Alan Modra
2022-04-08 22:28 ` Tulio Magno Quites Machado Filho
2022-02-28 6:40 ` [PATCH v2 3/4] powerpc: Relocate stinfo->main Alan Modra
2022-04-08 22:32 ` Tulio Magno Quites Machado Filho
2022-02-28 6:40 ` [PATCH v2 4/4] powerpc64: Enable static-pie Alan Modra
2022-04-08 22:49 ` Tulio Magno Quites Machado Filho
2022-04-14 1:16 ` Alan Modra
2022-04-14 3:42 ` Fangrui Song
2022-04-20 7:21 ` [PATCH v3] " Alan Modra
2022-03-04 12:48 ` [PATCH v2 0/4] PowerPC64 static-pie Alan Modra
2022-04-08 8:06 ` Alan Modra
2022-04-09 0:14 ` Fangrui Song
2022-04-14 0:33 ` Alan Modra
2022-04-14 1:54 ` DT_RELR without libc.so dependency H.J. Lu
2022-04-14 3:43 ` Fangrui Song
2022-04-14 5:18 ` Alan Modra [this message]
2022-04-14 17:55 ` H.J. Lu
2022-04-08 22:27 ` [PATCH v2 0/4] PowerPC64 static-pie Tulio Magno Quites Machado Filho
2022-04-11 1:38 ` Alan Modra
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