From: Cary Coutant <ccoutant@gmail.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Fangrui Song <maskray@google.com>,
libc-alpha@sourceware.org, binutils@sourceware.org
Subject: Re: [PATCH] elf: Support DT_RELR relative relocation format [BZ #27924]
Date: Tue, 26 Oct 2021 16:28:29 -0700 [thread overview]
Message-ID: <CAJimCsHBOZNNdU-DYL1j3eTrNH8bawkkG1hUwNd2=G-cJuNxyQ@mail.gmail.com> (raw)
In-Reply-To: <3368ef30-eb8c-8828-1af0-1a227d99dc93@suse.com>
> While in line with the proposed spec additions I'm afraid the uses of
> ElfW(Addr) here aren't universally correct: You assume that ELF
> container type (size) expresses an aspect of the ABI. While this is
> indeed the case for several arch-es, I think this has been a mistake.
> IA-64, while meanwhile mostly dead, is (was) an example where 64-bit
> code can validly live in a 32-bit ELF container (at least as far as
> the psABI is concerned; I have no idea whether glibc actually
> followed the spec). There's a separate ELF header flag indicating the
> ABI, and hence the size of a pointer.
The IA-64 ABI specifically requires the class of the container
(ELFCLASS32 vs ELFCLASS64) to match the runtime model for executable
objects. It's allowable to use ELFCLASS32 for 64-bit relocatable
objects, but not for executable objects. Thus, I think it's quite
reasonable to spec it this way, and it really isn't any different from
a non-RELR relocation. For executables, there really are strong ties
between the ELF container size and the runtime model.
One point that I don't think has been raised yet is that some
platforms, like IA-64, may have more than one RELATIVE relocation.
IA-64 has four -- R_IA64_REL{32|64}{MSB|LSB} -- only one of which
would be eligible (or expected) in a RELR context. I'm thinking that a
DT_RELRTYPE entry specifying the relocation type might be called for,
just to make it explicit. I suppose it could be optional for platforms
where there is only one choice of R_XXX_RELATIVE.
-cary
next prev parent reply other threads:[~2021-10-26 23:28 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-08 6:57 Fangrui Song
2021-10-08 15:39 ` Florian Weimer
2021-10-08 16:36 ` Fangrui Song
2021-10-08 19:41 ` Cary Coutant
2021-10-08 16:51 ` H.J. Lu
2021-10-08 17:37 ` Fangrui Song
2021-10-08 17:43 ` H.J. Lu
2021-10-08 18:46 ` Fangrui Song
2021-10-11 7:48 ` Jan Beulich
2021-10-11 18:43 ` Fāng-ruì Sòng
2021-10-11 22:08 ` Joseph Myers
2021-10-12 8:14 ` Jan Beulich
2021-10-12 8:18 ` Jan Beulich
2021-10-12 14:09 ` H.J. Lu
2021-10-12 16:07 ` Fāng-ruì Sòng
2021-10-13 6:00 ` Jan Beulich
2021-10-13 6:13 ` Fāng-ruì Sòng
2021-10-13 6:18 ` Fāng-ruì Sòng
2021-10-18 7:59 ` Jan Beulich
2021-10-16 20:22 ` Fangrui Song
2021-10-26 23:28 ` Cary Coutant [this message]
2021-10-11 21:47 ` Joseph Myers
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