From: Florian Weimer <fweimer@redhat.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: "H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>,
Binutils <binutils@sourceware.org>
Subject: Re: RFC: Add GNU_PROPERTY_1_GLIBC_2_NEEDED
Date: Thu, 28 Oct 2021 16:08:32 +0200 [thread overview]
Message-ID: <87k0hxkzrz.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <CAMe9rOqzgfNrGOp2U21bKMkJQRSzBOu95BMUxBd2_=tj_V9bSQ@mail.gmail.com> (H. J. Lu's message of "Thu, 28 Oct 2021 06:37:48 -0700")
* H. J. Lu:
> I am not sure if I am following your concerns. We have an ELF feature,
> like DT_RELR, which is tied to a glibc version. The binary with DT_RELR
> will crash with the older glibcs. And you DON'T want such a binary with
> a dependency on the required glibc version. Can you tell me why?
Historically, such features have not been tied to a glibc version. CET,
DT_AUDIT, AArch64 variant PCS support, nearly arbitrary calling
convention support on x86-64 all are not really version-specific (they
have been backported to varying degrees), and those involve dynamic
linker features.
In contrast, if DT_RELR support is indicated by a GLIBC_2.35 version
dependency, it is necessary to backport all of the GLIBC_2.35 symbol set
as part of the DT_RELR backport. This means such backports are usually
not feasible.
>> >> The problem that linkers and loaders ignore unknown types should be
>> >> tackled in a different way, e.g. by flagging critical types in some way.
>> >> See:
>> >>
>> >> Critical program headers and dynamic tags
>> >> <https://groups.google.com/g/generic-abi/c/vdG_G4l3N-Y/m/SB3DurdbBAAJ>
>> >>
>> >
>> > This won't help the existing ld.so binaries which this proposal
>> > is addressing.
>>
>> We need to increase the ABI version once, to signal the requirement for
>> critical tags checking.
>>
>
> Which ABI version? .note.ABI-tag or EI_ABIVERSION? A binary linked
> against glibc 2.40 without DT_RELR can run with glibc 2.34. But a binary
> linked against glibc 2.30 with DT_RELR won't run with glibc 2.34 at all.
> Increasing the ABI version doesn't solve the DT_RELR issue.
The way EI_ABIVERSION works is that the link editor produces the minimum
version needed by the features in the binary.
So if the link editor DT_RELR, it would produce a DT_CRITICAL_DT tag for
DT_RELR and set EI_ABIVERSION for critical DT tag support. Similar for
other critical DT Tags. If no critical DT tags are used, an earlier
EI_ABIVERSION can be used.
Thanks,
Florian
next prev parent reply other threads:[~2021-10-28 14:08 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-26 14:53 H.J. Lu
2021-10-26 15:25 ` Florian Weimer
2021-10-26 15:51 ` H.J. Lu
2021-10-26 18:39 ` v2: " H.J. Lu
2021-10-28 6:55 ` Florian Weimer
2021-10-28 13:37 ` H.J. Lu
2021-10-28 14:08 ` Florian Weimer [this message]
2021-10-28 14:17 ` H.J. Lu
2021-10-28 14:20 ` H.J. Lu
2021-10-29 18:11 ` Florian Weimer
2021-10-29 12:47 ` Michael Matz
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