[Buildroot] compiler plugins & compiling the kernel

[Arnout Vandecappelle]

On 21-08-16 05:43, Kenneth Adam Miller wrote:
> On Sat, Aug 20, 2016 at 6:39 PM, Kenneth Adam Miller
> <kennethadammiller at gmail.com> wrote:
>> On Sat, Aug 20, 2016 at 2:01 PM, Thomas Petazzoni
>> <thomas.petazzoni at free-electrons.com> wrote:
>>> Hello,
>>>
>>> On Sat, 20 Aug 2016 13:10:07 -0400, Kenneth Adam Miller wrote:
[snip]
>>>> In addition, for some pax related options, it requires gcc plugins for
>>>> the version being used. That means that I would have to have plugin
>>>> support for my host, correct?
>>>
>>> No, you would need support for plugins in the cross-compiler.
>>>
>>
>> We have been building gr-security modded kernels for some time on a
>> different machine with gcc 4.8, but I'm having this confusion; does
>> the buildroot internal compiler support that? Because I'm getting an
>> error in buildroot indicating that compiler plugins must be supported,
>> and I'm using the buildroot internal compiler with version 5.x, it
>> confused me a little bit.
>>
> 
> I found the exact output that brought about the build error.
> 
>>>> linux-headers 3.14.51 Configuring...
> ...
> make[2]: Entering directory ... build/linux-headers-3.14.51
> Makefile:652 *** Your gcc installation does not support plugins. If
> the necessary headers for plugin support are missing, they should be
> installed. On Debian, apt-get install gcc-<ver>-plugin-dev. If you
> choose to ignore this error and...

 Ah, this is annoying...

 When installing linux-headers, we don't pass the cross-compilation arguments,
because the cross-compiler doesn't exist yet at that point. So the installation
will use the host compiler instead for that check. Which is of course wrong.

 Well, actually it's a bug in gr-security, because this check shouldn't be done
for install_headers (gcc isn't even called).

> 
>>>> I don't believe that there is a way to
>>>> enable plugin support for the buildroot toolchain or for crosstool. At
>>>> least, when I looked and searched I didn't see any option that
>>>> mentioned that. I just want to make sure that I have it correct in
>>>> that my host compiler is being used to build the kernel.
>>>
>>> You're not correct. Support for plugins should be added to the
>>> cross-compiler if you need plugin support to build your kernel.
>>>
>>
>> That doesn't appear to be an option in buildroot.

 Well, we pass --enable-plugins when BR2_GCC_ENABLE_LTO is set. We don't pass
--disable-plugins so it really depends on the gcc defaults. But then, we don't
install the plugin development headers to HOST_DIR, so it will probably be
difficult to actually compile a plugin.

 Regards,
 Arnout

-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
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