Re: [PATCH] modpost.c: Add .text.unlikely to TEXT_SECTIONS

Tom Rini
2013-05-01T11:17:57Z

On 04/30/2013 10:19 PM, Rusty Russell wrote:
> Tom Rini <trini@ti.com> writes:
>> On 04/28/2013 10:59 PM, Rusty Russell wrote:
>>> Tom Rini <trini@ti.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.
>
> Weird, did you turn on CONFIG_GCOV_KERNEL? AFAICT you shouldn't see
> this section without that.

Nope, CONFIG_GCOV_KERNEL is off. Must be related to whatever flags the
Linaro folks set as default on -O2 (at least in their 2013.03 release),
after reading over one of the .o.cmd files in the build.

Do you want me to re-word the commit message a bit or ? Thanks!

--
Tom