linux-kernel - Re: [PATCH] modpost.c: Add .text.unlikely to TEXT

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Date:	Mon, 29 Apr 2013 09:15:12 -0400
From:	Tom Rini <trini@...com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	<linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] modpost.c: Add .text.unlikely to TEXT_SECTIONS

On 04/28/2013 10:59 PM, Rusty Russell wrote:
> Tom Rini <trini@...com> writes:
> 
>> Recent gcc's may place functions into the .text.unlikely section and we
>> need to check this section as well for section mismatches now otherwise
>> we may have false negatives for this test.
> 
> Hmm, I don't think it's all that recent, is it?  I can find it back to
> gcc 4.0.4:
> 
> `-freorder-functions'
>      Reorder functions in the object file in order to improve code
>      locality.  This is implemented by using special subsections
>      `.text.hot' for most frequently executed functions and
>      `.text.unlikely' for unlikely executed functions.  Reordering is
>      done by the linker so object file format must support named
>      sections and linker must place them in a reasonable way.
> 
>      Also profile feedback must be available in to make this option
>      effective.  See `-fprofile-arcs' for details.
> 
>      Enabled at levels `-O2', `-O3', `-Os'.
> 
> The comment is the same in in gcc 4.7.
> 
> So is your real issue that this section is generated with
> -fprofile-arcs, or has something changed with gcc 4.8, or...?

I've started seeing this with Linaro based 4.7 toolchains.  I can go
back through their releases and see when it starts showing up there if
it helps.  I didn't add .text.hot as I didn't have that section at all,
fwiw.

-- 
Tom
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