[Buildroot] [PATCH RFC] linux: disable attribute alias with gcc >= 8.1

Romain Naour romain.naour at gmail.com
Sat Jun 2 14:19:41 UTC 2018

Hi Thomas,

Le 01/06/2018 à 23:12, Thomas Petazzoni a écrit :
> Hello Romain,
> On Thu, 31 May 2018 22:37:45 +0200, Romain Naour wrote:
>> gcc-8 started warning about function aliases that have a non-matching
>> prototype. This seems rather useful in general, but it causes tons of
>> warnings in the Linux kernel, where we rely on abusing those aliases
>> for system call entry points, in order to sanitze the arguments passed
>> from user space in registers.
>> See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82435
>> Add a new conditional patch that disable the attribute-alias warning
>> introduced by gcc-8 by adding -Wno-attribute-alias to KBUILD_CFLAGS.
>> Signed-off-by: Romain Naour <romain.naour at gmail.com>
>> Cc: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
>> ---
>> Fixes most of build errors reported by toolchains-builder on Gitlab.
>> https://gitlab.com/free-electrons/toolchains-builder/pipelines/22921464
> Thanks, but unfortunately, it doesn't fix a lot of those build errors,
> because your patch doesn't apply as soon as the Linux kernel version is
> a bit different.
> For example, if you take qemu_mips32r2el_malta_defconfig, which builds
> a 4.11.3 kernel, your patch doesn't apply, and so the bug appears.
> So instead, I would like to suggest something like this:
> ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_8),y)
> LINUX_MAKE_ENV += KCFLAGS=-Wno-attribute-alias
> endif
> which works without any patch, and therefore works with potentially all
> kernel versions.

Thanks for KCFLAGS, I missed it and tried to use KBUILD_CFLAGS directly...
I wanted to not override KBUILD_CFLAGS from linux.mk to not lose CFLAGS defined
in the Makefile, that is why I use an conditional patch (which is not great).

I'll resend a v2.

Best regards,

> Best regards,
> Thomas

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