From: Michael Matz <matz@suse.de>
To: Nick Clifton <nickc@redhat.com>
Cc: binutils@sourceware.org, mjw@fedoraproject.org, amulhern@redhat.com
Subject: Re: RFC: Can static executables contain relocations against symbols ?
Date: Wed, 29 Mar 2023 16:00:12 +0000 (UTC) [thread overview]
Message-ID: <alpine.LSU.2.20.2303291542520.16810@wotan.suse.de> (raw)
In-Reply-To: <87v8ijmxjh.fsf@redhat.com>
Hello,
On Wed, 29 Mar 2023, Nick Clifton via Binutils wrote:
> Can static executables contain relocations against symbols ?
Generally I agree with you that they should not. Only symbol-less
relocations make sense (not all of them will be absolute, though. In PIEs
they will be base-relative, still symbolless of course). But for the sake
of discussion let's assume we somehow want to allow symbol-based relocs
nevertheless. Then:
In final-linked ELF files symbol headers always have to be optional. The
place of relocations, if necessary, (and symbols) needs to be communicated
in a different way anyway (on dynamic ELF files via the program headers
and dynamic entries, on static files via some other side channel, like
hardcoding the offset/addresses of the interesting pieces).
But: there is another observation that makes the Rust output invalid. An
allocated (SHF_ALLOC) section (here .got.rela) _must_ only refer to
allocated sections via its sh_link field. The .symtab section in the
example at hand was not SHF_ALLOC. So that's another bug.
Leaving a sh_link field of an SHT_RELA section to be zero seems a bit
dubious. Normally client code would be able to rely on sh_link containing
an existing section index. OTOH SHN_UNDEF (i.e. zero) _is_ somewhat of a
section index, so leaving it as zero might just be fine.
So, even if the above problems would be fixed I think your patch still
makes sense. Perhaps add another check to only leave it zero if
elf_onesymtab is not allocated itself.
Ciao,
Michael.
next prev parent reply other threads:[~2023-03-29 16:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-29 14:39 Nick Clifton
2023-03-29 15:47 ` Mark Wielaard
2023-03-29 16:00 ` Michael Matz [this message]
2023-03-30 1:22 ` Alan Modra
2023-03-30 4:54 ` Alan Modra
2023-03-30 8:57 ` Nick Clifton
2023-03-30 9:12 ` Alan Modra
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