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From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: Fangrui Song <maskray@google.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
	Florian Weimer <fweimer@redhat.com>,
	Wilco Dijkstra via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [RESEND PATCH] Makeconfig: Set pie-ccflag to -fPIE by default
Date: Tue, 20 Sep 2022 13:59:45 +0000	[thread overview]
Message-ID: <AS4PR08MB79012BF67DAA9CB0B72F8928834C9@AS4PR08MB7901.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20220915214513.s6uzsy2zvcnevolx@google.com>

Hi Fangrui,

> In Clang, -fpic/-fPIC without  -fno-semantic-interposition still allows
> interprocedural optimizations of default visibility external linkage definitions.
>
> It is unfortunate that GCC doesn't allow it and
> --enable-default-semantic-interposition is rejected (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100937)

I think it now does it with -Ofast, so that's a start at least...

> So if such an option -ffast-PIC is made, it will only benefit GCC.
> I have a long write-up in https://maskray.me/blog/2021-05-09-fno-semantic-interposition#in-action

Well if changing the default of fPIC is unacceptable in GCC, adding a new option
should help LLVM too since it could imply more than -fno-semantic-interposition.
A key question is whether we could require that exported symbols are marked
explicitly so that we only emit GOT and PLT indirections on such exported symbols.

Cheers,
Wilco

  reply	other threads:[~2022-09-20 14:00 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-26 18:39 Wilco Dijkstra
2022-08-26 19:02 ` H.J. Lu
2022-08-26 19:45   ` Richard Henderson
2022-08-26 20:11     ` H.J. Lu
2022-08-29 11:49       ` Wilco Dijkstra
2022-08-29 13:10         ` Florian Weimer
2022-08-29 15:27           ` Wilco Dijkstra
2022-08-29 15:27             ` Wilco Dijkstra
2022-08-29 19:43             ` H.J. Lu
2022-08-29 19:57               ` Fangrui Song
2022-09-05  8:58                 ` Wilco Dijkstra
2022-09-15 21:45                   ` Fangrui Song
2022-09-20 13:59                     ` Wilco Dijkstra [this message]
2022-09-20 14:12                       ` Florian Weimer
2022-09-20 16:00                         ` Wilco Dijkstra
2022-09-20 22:02                           ` Fangrui Song
  -- strict thread matches above, loose matches on Subject: below --
2022-08-25 21:01 Richard Henderson
2022-08-26 12:32 ` Adhemerval Zanella Netto
2022-08-26 17:29   ` Richard Henderson

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