From: Sriraman Tallam <tmsriram@google.com>
To: Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
Cc: Jan Hubicka <hubicka@ucw.cz>, "H.J. Lu" <hjl.tools@gmail.com>,
Pedro Alves <palves@redhat.com>, Michael Matz <matz@suse.de>,
David Li <davidxl@google.com>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [RFC][PATCH][X86_64] Eliminate PLT stubs for specified external functions via -fno-plt=
Date: Mon, 01 Jun 2015 18:01:00 -0000 [thread overview]
Message-ID: <CAAs8Hmy3jZDkE1hNmojx9rBBAZ9tjCYHXHevojMTAYHZ5kp8hA@mail.gmail.com> (raw)
In-Reply-To: <556C16B1.5080606@arm.com>
On Mon, Jun 1, 2015 at 1:24 AM, Ramana Radhakrishnan
<ramana.radhakrishnan@arm.com> wrote:
>
>>> Why isn't it just an indirect call in the cases that would require a GOT
>>> slot and a direct call otherwise ? I'm trying to work out what's so
>>> different on each target that mandates this to be in the target backend.
>>> Also it would be better to push the tests into gcc.dg if you can and
>>> check
>>> for the absence of a relocation so that folks at least see these as being
>>> UNSUPPORTED on their target.
>>
>>
>
>
> To be even more explicit, shouldn't this be handled similar to the way in
> which -fno-plt is handled in a target agnostic manner ? After all, if you
> can handle this for the command line, doing the same for a function which
> has been decorated with attribute((noplt)) should be simple.
-fno-plt does not work for non-PIC code, having non-PIC code not use
PLT was my primary motivation. Infact, if you go back in this thread,
I suggested to HJ if I should piggyback on -fno-plt. I tried using
the -fno-plt implementation to do this by removing the flag_pic check
in calls.c, but that does not still work for non-PIC code.
>
>> I am not familiar with PLT calls for other targets. I can move the
>> tests to gcc.dg but what relocation are you suggesting I check for?
>
>
> Move the test to gcc.dg, add a target_support_no_plt function in
> testsuite/lib/target-supports.exp and mark this as being supported only on
> x86 and use scan-assembler to scan for PLT relocations for x86. Other
> targets can add things as they deem fit.
>
> In any case, on a large number of elf/ linux targets I would have thought
> the absence of a JMP_SLOT relocation would be good enough to check that this
> is working correctly.
>
> regards
> Ramana
>
>
>
>
>>
>> Thanks
>> Sri
>>
>>
>>>
>>>
>>>
>>> Ramana
>>>>
>>>>
>>>>>
>>>>> Also I think the PLT calls have EBX in call fusage wich is added by
>>>>> ix86_expand_call.
>>>>> else
>>>>> {
>>>>> /* Static functions and indirect calls don't need the pic
>>>>> register. */
>>>>> if (flag_pic
>>>>> && (!TARGET_64BIT
>>>>> || (ix86_cmodel == CM_LARGE_PIC
>>>>> && DEFAULT_ABI != MS_ABI))
>>>>> && GET_CODE (XEXP (fnaddr, 0)) == SYMBOL_REF
>>>>> && ! SYMBOL_REF_LOCAL_P (XEXP (fnaddr, 0)))
>>>>> {
>>>>> use_reg (&use, gen_rtx_REG (Pmode,
>>>>> REAL_PIC_OFFSET_TABLE_REGNUM));
>>>>> if (ix86_use_pseudo_pic_reg ())
>>>>> emit_move_insn (gen_rtx_REG (Pmode,
>>>>> REAL_PIC_OFFSET_TABLE_REGNUM),
>>>>> pic_offset_table_rtx);
>>>>> }
>>>>>
>>>>> I think you want to take that away from FUSAGE there just like we do
>>>>> for
>>>>> local calls
>>>>> (and in fact the code should already check flag_pic && flag_plt I
>>>>> suppose.
>>>>
>>>>
>>>> Done that now and patch attached.
>>>>
>>>> Thanks
>>>> Sri
>>>>
>>>>>
>>>>> Honza
>>
>>
>
next prev parent reply other threads:[~2015-06-01 18:01 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-10 15:19 H.J. Lu
[not found] ` <CAAs8HmwWSDY+KjKcB4W=TiYV0Pz7NSvfL_8igp+hPT-LU1utTg@mail.gmail.com>
2015-05-21 21:31 ` Sriraman Tallam
2015-05-21 21:39 ` Sriraman Tallam
2015-05-21 22:02 ` Pedro Alves
2015-05-21 22:02 ` Jakub Jelinek
2015-05-22 1:47 ` H.J. Lu
2015-05-22 3:38 ` Xinliang David Li
2015-05-21 22:34 ` Sriraman Tallam
2015-05-22 9:22 ` Pedro Alves
2015-05-22 15:13 ` Sriraman Tallam
2015-05-28 18:53 ` Sriraman Tallam
2015-05-28 19:05 ` H.J. Lu
2015-05-28 19:48 ` Sriraman Tallam
2015-05-28 20:19 ` H.J. Lu
2015-05-28 21:27 ` Sriraman Tallam
2015-05-28 21:31 ` H.J. Lu
2015-05-28 21:52 ` Sriraman Tallam
2015-05-28 22:48 ` H.J. Lu
2015-05-29 3:51 ` Sriraman Tallam
2015-05-29 5:13 ` H.J. Lu
2015-05-29 7:13 ` Sriraman Tallam
2015-05-29 17:36 ` Sriraman Tallam
2015-05-29 17:52 ` H.J. Lu
2015-05-29 18:33 ` Sriraman Tallam
2015-05-29 20:50 ` Jan Hubicka
2015-05-29 22:56 ` Sriraman Tallam
2015-05-29 23:08 ` Sriraman Tallam
[not found] ` <CAJA7tRYsMiq7rx34c=z6KwRdwYxxaeP6Z6qzA4XEwnJSMT7z=Q@mail.gmail.com>
2015-05-30 4:44 ` Sriraman Tallam
2015-06-01 8:24 ` Ramana Radhakrishnan
2015-06-01 18:01 ` Sriraman Tallam [this message]
2015-06-01 18:41 ` Ramana Radhakrishnan
2015-06-01 18:55 ` Sriraman Tallam
2015-06-01 20:33 ` Ramana Radhakrishnan
2015-06-02 18:27 ` Sriraman Tallam
2015-06-02 19:59 ` Bernhard Reutner-Fischer
2015-06-02 20:09 ` Sriraman Tallam
2015-06-02 21:18 ` Bernhard Reutner-Fischer
2015-06-02 21:09 ` Ramana Radhakrishnan
2015-06-02 21:25 ` Xinliang David Li
2015-06-02 21:52 ` Bernhard Reutner-Fischer
2015-06-02 21:40 ` Sriraman Tallam
2015-06-03 14:37 ` Ramana Radhakrishnan
2015-06-03 18:53 ` Sriraman Tallam
2015-06-03 20:16 ` Richard Henderson
2015-06-03 20:59 ` Sriraman Tallam
2015-06-04 16:56 ` Sriraman Tallam
2015-06-04 17:30 ` Richard Henderson
2015-06-04 21:34 ` Sriraman Tallam
2015-07-24 19:02 ` H.J. Lu
2015-06-03 19:57 ` Richard Henderson
-- strict thread matches above, loose matches on Subject: below --
2015-05-01 0:31 Sriraman Tallam
2015-05-01 3:21 ` Alan Modra
2015-05-01 3:26 ` Sriraman Tallam
2015-05-01 15:01 ` Andi Kleen
2015-05-01 16:19 ` Xinliang David Li
2015-05-01 16:23 ` H.J. Lu
2015-05-01 16:26 ` Xinliang David Li
2015-05-01 18:06 ` Sriraman Tallam
2015-05-02 12:12 ` Andi Kleen
2015-05-01 17:50 ` Sriraman Tallam
2015-05-04 14:45 ` Michael Matz
2015-05-04 16:43 ` Xinliang David Li
2015-05-04 16:58 ` Michael Matz
2015-05-04 17:22 ` Xinliang David Li
2015-05-09 16:35 ` H.J. Lu
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