From: Ramana Radhakrishnan <ramana.gcc@googlemail.com>
To: Richard Sandiford <richard.sandiford@arm.com>,
Wilco Dijkstra <Wilco.Dijkstra@arm.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>,
"maskray@google.com" <maskray@google.com>
Subject: Re: [PATCH] AArch64: Add support for -mdirect-extern-access
Date: Thu, 17 Nov 2022 20:52:34 +0000 [thread overview]
Message-ID: <CAJA7tRYTuQo_Q6P78eDkOh-qRbySOU0RFEm-ktZT8Te5E2ZDyg@mail.gmail.com> (raw)
In-Reply-To: <mpty1s9ebfb.fsf@arm.com>
On Thu, Nov 17, 2022 at 5:30 PM Richard Sandiford via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Wilco Dijkstra <Wilco.Dijkstra@arm.com> writes:
> > Hi Richard,
> >
> >> Can you go into more detail about:
> >>
> >> Use :option:`-mdirect-extern-access` either in shared libraries or in
> >> executables, but not in both. Protected symbols used both in a shared
> >> library and executable may cause linker errors or fail to work correctly
> >>
> >> If this is LLVM's default for PIC (and by assumption shared libraries),
> >> is it then invalid to use -mdirect-extern-access for any PIEs that
> >> are linked against those shared libraries and use protected symbols
> >> from those libraries? How would a user know that one of the shared
> >> libraries they're linking against was built in this way?
> >
> > Yes, the usage model is that you'd either use it for static PIE or only on
> > data that is not shared. If you get it wrong them you'll get the copy
> > relocation error.
>
> Thanks. I think I'm still missing something though. If, for the
> non-executable case, people should only use the feature on data that
> is not shared, why do we need to relax the binds-local condition for
> protected symbols on -fPIC? Oughtn't the symbol to be hidden rather
> than protected if the data isn't shared?
>
> I can understand the reasoning for the PIE changes but I'm still
> struggling with the PIC-but-not-PIE bits.
I think I'm with Richard S on hidden vs protected on first reading. I
can see why this works out of the box and can even be default for
static-pie.
Any reason why this is not on by default - it's early enough in the
stage3 cycle and we can always flip the defaults if there are more
problems found.
You probably need a rebase for the documentation bits,.
regards
Ramana
Ramana
next prev parent reply other threads:[~2022-11-17 20:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-11 14:48 Wilco Dijkstra
2022-11-16 10:54 ` Richard Sandiford
2022-11-17 16:42 ` Wilco Dijkstra
2022-11-17 17:30 ` Richard Sandiford
2022-11-17 20:52 ` Ramana Radhakrishnan [this message]
2022-11-17 21:20 ` maskray
2022-11-17 21:37 ` Andrew Pinski
2022-11-17 21:46 ` Fangrui Song
2022-11-17 21:55 ` Andrew Pinski
2022-11-17 22:07 ` Fangrui Song
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