From: Samuel Thibault <samuel.thibault@ens-lyon.org>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: libc-alpha@sourceware.org, Szabolcs Nagy <szabolcs.nagy@arm.com>,
rrh.henry@gmail.com
Subject: Re: RFC: Remove --disable-hidden-plt
Date: Tue, 6 Apr 2021 19:18:33 +0200 [thread overview]
Message-ID: <20210406171833.24b5vr4j2b762knb@begin> (raw)
In-Reply-To: <28ab0b62-2b14-4fd2-b333-abb1d91fa714@linaro.org>
Adhemerval Zanella via Libc-alpha, le mar. 06 avril 2021 14:12:41 -0300, a ecrit:
>
>
> On 03/04/2021 14:41, H.J. Lu via Libc-alpha wrote:
> > --disable-hidden-plt was added by
> >
> > commit 749a9a4fbfd261e2d9811d9bc4507478c2f7cc58
> > Author: Roland McGrath <roland@gnu.org>
> > Date: Tue Oct 1 08:45:44 2002 +0000
> >
> > 2002-10-01 Roland McGrath <roland@frob.com>
> >
> > * config.h.in (NO_HIDDEN): New #undef.
> > * include/libc-symbols.h [! NO_HIDDEN]: Add this condition to
> > nonempty definitions of hidden_proto et al.
> > * configure.in: Grok --disable-hidden-plt to define NO_HIDDEN.
> > * configure: Regenerated.
> > * sysdeps/mach/hurd/configure.in: Always define NO_HIDDEN.
> > * sysdeps/mach/hurd/configure: Regenerated.
> >
> > It doesn't work on x86-64:
> >
> > https://sourceware.org/bugzilla/show_bug.cgi?id=27692
> >
> > Should it be removed?
> >
>
> My take is to remove it. Besides the reasons noted by Szabolcs [1],
> some symbols interposition are not really possible on some scenarios
> (for instance intra IFUNC call through hidden symbol on i686 and ppc32),
> it requires more development effort (as any configure switch and we
> will probably need a configure check to see if *all* supposed intra
> calls are actually being called through PLT and fix bugs with missing
> support), there is no clear advantage of providing such functionality,
> and it broken on every architecture for some time (at least since
> 2.27).
>
> However it seems it will still need to support it internally for
> Hurd
Yes, some symbols in ld.so (most of sysdeps/mach/hurd/dl-sysdep.c)
*need* to be interposed by the loaded libc.so, because the
implementation in ld.so is to be used only at bootstrap of the program,
and then overriden by the real full-fledged implementation.
Samuel
> and it does catch a potential issue where some implementation
> uses a non intended interface (such as __hidden_ver1).
>
> I tried to understand why Roland's has added it in the first place,
> but there is no discussion about it on libc-alpha in Sep/Oct 2002.
>
> [1] https://sourceware.org/bugzilla/show_bug.cgi?id=27692#c7
next prev parent reply other threads:[~2021-04-06 17:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-03 17:41 H.J. Lu
2021-04-06 17:12 ` Adhemerval Zanella
2021-04-06 17:18 ` Samuel Thibault [this message]
2021-04-06 17:39 ` Adhemerval Zanella
2021-04-06 18:03 ` Samuel Thibault
2021-04-06 18:15 ` Adhemerval Zanella
2021-04-06 18:43 ` Samuel Thibault
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