From: Sriraman Tallam <tmsriram@google.com>
To: ramrad01@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: Sat, 30 May 2015 04:44:00 -0000 [thread overview]
Message-ID: <CAAs8HmxB9NyJQHRxTLj4gKntDgwFfri0VvwSR6vfA1HDTpFHaQ@mail.gmail.com> (raw)
In-Reply-To: <CAJA7tRYsMiq7rx34c=z6KwRdwYxxaeP6Z6qzA4XEwnJSMT7z=Q@mail.gmail.com>
On Fri, May 29, 2015 at 3:24 PM, Ramana Radhakrishnan
<ramana.gcc@googlemail.com> wrote:
>
>
> On Friday, 29 May 2015, Sriraman Tallam <tmsriram@google.com> wrote:
>>
>> On Fri, May 29, 2015 at 12:35 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> >> * config/i386/i386.c (avoid_plt_to_call): New function.
>> >> (ix86_output_call_insn): Generate indirect call for functions
>> >> marked with "noplt" attribute.
>> >> (attribute_spec ix86_attribute_): Define new attribute "noplt".
>> >> * doc/extend.texi: Document new attribute "noplt".
>> >> * gcc.target/i386/noplt-1.c: New testcase.
>> >> * gcc.target/i386/noplt-2.c: New testcase.
>> >>
>> >> Index: config/i386/i386.c
>> >> ===================================================================
>> >> --- config/i386/i386.c (revision 223720)
>> >> +++ config/i386/i386.c (working copy)
>> >> @@ -25599,6 +25599,24 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx
>> >> call
>> >> return call;
>> >> }
>> >>
>> >> +/* Return true if the function being called was marked with attribute
>> >> + "noplt". If this function is defined, this should return false.
>> >> */
>> >> +static bool
>> >> +avoid_plt_to_call (rtx call_op)
>> >> +{
>> >> + if (SYMBOL_REF_LOCAL_P (call_op))
>> >> + return false;
>> >> +
>> >> + tree symbol_decl = SYMBOL_REF_DECL (call_op);
>> >> +
>> >> + if (symbol_decl != NULL_TREE
>> >> + && TREE_CODE (symbol_decl) == FUNCTION_DECL
>> >> + && lookup_attribute ("noplt", DECL_ATTRIBUTES (symbol_decl)))
>> >> + return true;
>> >> +
>> >> + return false;
>> >> +}
>> >
>> > OK, now we have __attribute__ (optimize("noplt")) which binds to the
>> > caller and makes
>> > all calls in the function to skip PLT and __attribute__ ("noplt") which
>> > binds to callee
>> > and makes all calls to function to not use PLT.
>> >
>> > That sort of makes sense to me, but why "noplt" attribute is not
>> > implemented at generic level
>> > just like -fplt? Is it only because every target supporting PLT would
>> > need update in its
>> > call expansion patterns?
>>
>> Yes, that is what I had in mind.
>>
>
>
> 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.
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?
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:[~2015-05-29 23:36 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 [this message]
2015-06-01 8:24 ` Ramana Radhakrishnan
2015-06-01 18:01 ` Sriraman Tallam
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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