From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Fangrui Song <maskray@google.com>,
"H.J. Lu" <hjl.tools@gmail.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 16:00:34 +0000 [thread overview]
Message-ID: <AS4PR08MB79019A23A4122594A16FB66B834C9@AS4PR08MB7901.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <87a66um8wz.fsf@oldenburg.str.redhat.com>
Hi Florian,
>> 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.
>
> -flto with a linker plugin already covers this. I don't think we need
> anything else. Maybe an LTO mode that only deals with visibility, but
> otherwise does little cross-TU optimization?
Well it would be great if LTO solved this problem, but unfortunately it can't...
LTO tells you which symbols are locally defined, but this doesn't help PIC.
Local definitions with default visibility must still indirect via the GOT/PLT,
similarly interprocedural optimizations are still blocked.
A LTO-lite option that just deals with visibility and global variable optimization
(eg. better use of anchors) and other cheap optimizations seems useful indeed.
Cheers,
Wilco
next prev parent reply other threads:[~2022-09-20 16:00 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
2022-09-20 14:12 ` Florian Weimer
2022-09-20 16:00 ` Wilco Dijkstra [this message]
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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