From: "H.J. Lu" <hjl.tools@gmail.com>
To: Jeff Law <law@redhat.com>
Cc: Alexander Monakov <amonakov@ispras.ru>,
Jakub Jelinek <jakub@redhat.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
Rich Felker <dalias@libc.org>
Subject: Re: [PATCH] Expand PIC calls without PLT with -fno-plt
Date: Thu, 07 May 2015 19:13:00 -0000 [thread overview]
Message-ID: <CAMe9rOqGgK1ueyxaBO21hzOhNQYxDofavWs1vnScQOO8QbG4=A@mail.gmail.com> (raw)
In-Reply-To: <554BAD59.50107@redhat.com>
On Thu, May 7, 2015 at 11:22 AM, Jeff Law <law@redhat.com> wrote:
> On 05/06/2015 09:24 AM, Alexander Monakov wrote:
>>
>> On Mon, 4 May 2015, Jeff Law wrote:
>>>
>>> On 05/04/2015 11:39 AM, Jakub Jelinek wrote:
>>>>
>>>> On Mon, May 04, 2015 at 11:34:05AM -0600, Jeff Law wrote:
>>>>>
>>>>> On 05/04/2015 10:37 AM, Alexander Monakov wrote:
>>>>>>
>>>>>> This patch introduces option -fno-plt that allows to expand calls that
>>>>>> would
>>>>>> go via PLT to load the address of the function immediately at call
>>>>>> site
>>>>>> (which
>>>>>> introduces a GOT load). Cover letter explains the motivation for this
>>>>>> patch.
>>>>>>
>>>>>> New option documentation for invoke.texi is missing from the patch; if
>>>>>> this is
>>>>>> accepted I'll be happy to send a v2 with documentation added.
>>>>>>
>>>>>> * calls.c (prepare_call_address): Transform PLT call to GOT lookup
>>>>>> and
>>>>>> indirect call by forcing address into a pseudo with -fno-plt.
>>>>>> * common.opt (flag_plt): New option.
>>>>>
>>>>> OK once you cobble together the invoke.texi changes.
>>>>
>>>>
>>>> Isn't what Michael/Alan suggested better? I mean as/ld/compiler changes
>>>> to
>>>> inline the plt slot's first part, then lazy binding will work fine.
>>>
>>> I must have missed Alan/Michael's message.
>>>
>>> ISTM the win here is that by going through the GOT, you can CSE the GOT
>>> reference and possibly get some more register allocation freedom. Is
>>> that
>>> still the case with Alan/Michael's approach?
>>
>>
>> If the same PLT stubs as today are to be used, it constrains the compiler
>> on
>> 32-bit x86 and possibly other arches where PLT stubs need GOT pointer in a
>> specific register. It's possible to imagine more complex PLT stubs that
>> obtain GOT pointer on their own, but in that case you can't let
>> optimizations
>> such as loop invariant motion move the GOT load away from the call in a
>> fashion that could result in PLT stub pointer be reused many times.
>>
>> Going ahead with this patch now allows anyone to play with no-PLT codegen
>> on
>> any architecture. As you can see from this series, on x86 it uncovered
>> several
>> codegen blunders (and fixing those should improve normal codegen as well
>> -- so
>> everybody wins).
>>
>> Below is my proposed patch for invoke.texi. Still OK to check in?
>>
>> * doc/invoke.texi (Code Generation Options): Add -fno-plt.
>> ([-fno-plt]): Document.
>
> We're not changing the defaults, so I think this is fine. Whether or not it
> proves useful is still to be determined.
>
We should do if we know -z now will be passed to linker and function
foo is defined in a shared library. Without the new relocation, we will
only know for sure if foo is defined in a shared library when we do LTO.
With the new relocation, we can do it for all non-local functions via a
compiler switch.
--
H.J.
next prev parent reply other threads:[~2015-05-07 19:13 UTC|newest]
Thread overview: 106+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-04 16:38 PIC calls without PLT, generic implementation Alexander Monakov
2015-05-04 16:38 ` [PATCH i386] Allow sibcalls in no-PLT PIC Alexander Monakov
2015-05-15 16:37 ` Alexander Monakov
2015-05-15 16:48 ` H.J. Lu
2015-05-15 20:08 ` Jan Hubicka
2015-05-15 20:23 ` H.J. Lu
2015-05-15 20:35 ` Rich Felker
2015-05-15 20:37 ` H.J. Lu
2015-05-15 20:45 ` Rich Felker
2015-05-15 22:16 ` H.J. Lu
2015-05-15 23:14 ` Jan Hubicka
2015-05-15 23:30 ` H.J. Lu
2015-05-15 23:35 ` H.J. Lu
2015-05-15 23:44 ` H.J. Lu
2015-05-16 0:18 ` Rich Felker
2015-05-16 14:33 ` H.J. Lu
2015-05-16 19:03 ` H.J. Lu
2015-05-16 19:32 ` Rich Felker
2015-05-16 23:23 ` H.J. Lu
2015-05-15 23:49 ` Rich Felker
2015-05-19 14:48 ` Michael Matz
2015-05-19 15:11 ` Jeff Law
2015-05-19 16:03 ` Michael Matz
2015-05-19 19:11 ` Rich Felker
2015-05-19 18:08 ` Rich Felker
2015-05-19 19:03 ` Richard Henderson
2015-05-19 19:10 ` H.J. Lu
2015-05-19 19:17 ` Richard Henderson
2015-05-19 19:20 ` H.J. Lu
2015-05-19 19:54 ` Richard Henderson
2015-05-19 20:27 ` Rich Felker
2015-05-19 20:44 ` H.J. Lu
2015-05-19 21:28 ` Rich Felker
2015-05-20 0:52 ` H.J. Lu
2015-05-20 1:09 ` Rich Felker
2015-05-22 19:32 ` Richard Henderson
2015-05-19 19:48 ` Rich Felker
2015-05-19 20:16 ` Richard Henderson
2015-05-20 12:13 ` Michael Matz
2015-05-20 12:40 ` H.J. Lu
2015-05-20 14:17 ` Rich Felker
2015-05-20 14:33 ` Michael Matz
2015-05-18 18:25 ` Alexander Monakov
2015-05-18 19:03 ` Jan Hubicka
2015-05-04 16:38 ` [PATCH] Expand PIC calls without PLT with -fno-plt Alexander Monakov
2015-05-04 17:34 ` Jeff Law
2015-05-04 17:40 ` Jakub Jelinek
2015-05-04 17:42 ` Jeff Law
2015-05-06 3:08 ` Rich Felker
2015-05-10 17:07 ` Jan Hubicka
2015-05-06 15:25 ` Alexander Monakov
2015-05-06 15:46 ` Jakub Jelinek
2015-05-06 15:55 ` Jeff Law
2015-05-06 16:44 ` Alexander Monakov
2015-05-06 17:35 ` Rich Felker
2015-05-06 18:26 ` H.J. Lu
2015-05-06 18:37 ` Rich Felker
2015-05-06 18:45 ` H.J. Lu
2015-05-06 19:01 ` Rich Felker
2015-05-06 19:05 ` H.J. Lu
2015-05-06 19:18 ` Rich Felker
2015-05-06 19:24 ` H.J. Lu
2015-05-11 11:48 ` Michael Matz
2015-05-11 14:20 ` Rich Felker
2015-05-07 18:22 ` Jeff Law
2015-05-07 19:13 ` H.J. Lu [this message]
2015-05-10 16:59 ` Jan Hubicka
2015-05-11 20:36 ` Jeff Law
2015-05-11 20:55 ` H.J. Lu
2015-05-11 22:13 ` Jan Hubicka
2015-06-22 15:52 ` Jiong Wang
2015-06-22 18:18 ` Alexander Monakov
2015-06-23 8:41 ` Ramana Radhakrishnan
2015-06-23 10:43 ` Alexander Monakov
2015-06-23 13:28 ` Jeff Law
2015-07-16 10:37 ` [AArch64] Tighten direct call pattern to repair -fno-plt Jiong Wang
2015-07-16 10:47 ` Alexander Monakov
2015-07-16 10:48 ` Jiong Wang
2015-07-21 12:52 ` [AArch64][sibcall]Tighten " Jiong Wang
2015-08-04 9:50 ` James Greenhalgh
2015-08-06 16:18 ` [COMMITTED][AArch64][sibcall]Tighten " Jiong Wang
2015-08-07 8:22 ` James Greenhalgh
2015-08-07 13:28 ` Jiong Wang
2015-08-04 9:50 ` [AArch64] Tighten " James Greenhalgh
2015-08-06 16:16 ` [COMMITTED][AArch64] " Jiong Wang
2015-05-04 16:38 ` [PATCH i386] Extend sibcall peepholes to allow source in %eax Alexander Monakov
2015-05-10 16:54 ` Jan Hubicka
2015-05-11 17:50 ` Alexander Monakov
2015-05-11 18:00 ` Jan Hubicka
2015-05-11 19:46 ` Uros Bizjak
2015-05-11 19:48 ` Jeff Law
2015-05-11 20:16 ` Jan Hubicka
2015-05-13 19:05 ` Alexander Monakov
2015-05-13 20:04 ` Jan Hubicka
2015-05-14 17:36 ` Alexander Monakov
2015-05-04 16:38 ` [PATCH i386] Move CLOBBERED_REGS earlier in register class list Alexander Monakov
2015-05-10 16:44 ` Jan Hubicka
2015-05-10 17:51 ` Uros Bizjak
2015-05-10 18:09 ` Uros Bizjak
2015-05-11 16:26 ` Alexander Monakov
2015-05-11 16:30 ` Uros Bizjak
2015-05-04 16:38 ` [PATCH i386] PR65753: allow PIC tail calls via function pointers Alexander Monakov
2015-05-10 16:37 ` Jan Hubicka
2015-05-11 16:11 ` Alexander Monakov
2015-05-04 16:38 ` [RFC PATCH] ira: accept loads via argp rtx in validate_equiv_mem Alexander Monakov
2015-05-04 17:37 ` Jeff Law
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAMe9rOqGgK1ueyxaBO21hzOhNQYxDofavWs1vnScQOO8QbG4=A@mail.gmail.com' \
--to=hjl.tools@gmail.com \
--cc=amonakov@ispras.ru \
--cc=dalias@libc.org \
--cc=gcc-patches@gcc.gnu.org \
--cc=jakub@redhat.com \
--cc=law@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).