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From: "arek at hiler dot eu" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug build/29456] missing DT_HASH section in shared objects
Date: Mon, 08 Aug 2022 11:33:51 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29456

--- Comment #2 from Arkadiusz Hiler <arek at hiler dot eu> ---
Hi, thanks for the reply. I wonder where the defaulting to having only
DT_GNU_HASH is coming from?

Quoting ld's man page:

       --hash-style=3Dstyle
           Set the type of linker's hash table(s).
           style can be either "sysv" for classic
           ELF ".hash" section, "gnu" for new style
           GNU ".gnu.hash" section or "both" for
           both the classic ELF ".hash" and new
           style GNU ".gnu.hash" hash tables.  The
           default depends upon how the linker was
           configured, but for most Linux based
           systems it will be "both".


and indeed `ld --help` claims:

    --hash-style=3DSTYLE          Set hash style to sysv/gnu/both.  Default=
: both

As a sidenote mold defaults to sysv style hashes[0] and the format is well
documented[1], whereas for the GNU-style one you have to read the sources of
one of the implementations or rely on blog posts.

The change also breaks existing software, not sure what glibc's stance is on
that.

[0]:
https://github.com/rui314/mold/blob/415673a49e24b1f4189000b9eb4fb1a36a69709=
3/elf/mold.h#L1475
[1]: https://refspecs.linuxfoundation.org/elf/gabi41.pdf section 5-21

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