[Buildroot] [PATCH v2 02/15] linux: disable Werror for powerpc kernels

[Arnout Vandecappelle <arnout@mind.be>]

On 08/05/2019 17:07, Romain Naour wrote:
> From patch [1] included in kernel >= 5.0:
> "The upcoming GCC 9 release extends the -Wmissing-attributes warnings
> (enabled by -Wall) to C and aliases: it warns when particular function
> attributes are missing in the aliases but not in their target.
> 
> In particular, it triggers for all the init/cleanup_module
> aliases in the kernel (defined by the module_init/exit macros),
> ending up being very noisy.
> 
> These aliases point to the __init/__exit functions of a module,
> which are defined as __cold (among other attributes). However,
> the aliases themselves do not have the __cold attribute.
> 
> Since the compiler behaves differently when compiling a __cold
> function as well as when compiling paths leading to calls
> to __cold functions, the warning is trying to point out
> the possibly-forgotten attribute in the alias."
> 
> Werror is set by default while building ppc kernel [2], but
> some warning can be introduced while building current kernel with
> newer compiler (for example building kernel 4.19 with gcc 9.1).
> 
> For the same reason why we remove Werror in packages's compiler
> flags. Building with Werror is not bulletproof when we start
> using a newer compiler that introduce new warnings.
> This is the case here.
> 
> Also this option is a bit strange since it's specific to ppc kernels:
> "The intention is to make it harder for people to inadvertantly
> introduce warnings in the arch/powerpc code."
> Other kernel developers on other arch may be interested by a
> similar/more generic option.
> 
> So, It's clearly intended for kernel developers.

 Since buildroot is *also* intended for kernel developers, I don't think this is
a good idea.

 In fact, I don't like us forcing any options on the user. All this overriding
of .config options in linux.mk (and busybox.mk as well) is IMO confusing and
limiting user's freedom. So I don't like it if .config overrides get added.

 Therefore, I prefer your v1 solution of just fixing the affected defconfigs.

 Regards,
 Arnout

> 
> Instead of backporting this patch [1] to kernel 4.19, select
> unconditionally the Kconfig option CONFIG_PPC_DISABLE_WERROR
> that allow to disable Werror.
> 
> Fixes:
> https://gitlab.com/kubu93/toolchains-builder/-/jobs/205435741
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=a6e60d84989fa0e91db7f236eda40453b0e44afa
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=ba55bd74360ea4b8b95e73ed79474d37ff482b36
> [3] https://gitlab.com/bootlin/toolchains-builder
> 
> Fix-suggested-by: Yann E. MORIN <yann.morin.1998@free.fr>
> Signed-off-by: Romain Naour <romain.naour@gmail.com>
> ---
> v2: add a shared fragment in board/fragments/linux and update
>     qemu ppc* defconfigs. (Arnout)
> 
> v3: commit log (Yann)
>     enable the option from linux.mk instead of the defconfig.
> ---
>  linux/linux.mk | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/linux/linux.mk b/linux/linux.mk
> index 51fd41fa15..85364451a8 100644
> --- a/linux/linux.mk
> +++ b/linux/linux.mk
> @@ -315,6 +315,8 @@ define LINUX_KCONFIG_FIXUP_CMDS
>  	$(LINUX_FIXUP_CONFIG_ENDIANNESS)
>  	$(if $(BR2_arm)$(BR2_armeb),
>  		$(call KCONFIG_ENABLE_OPT,CONFIG_AEABI,$(@D)/.config))
> +	$(if $(BR2_powerpc)$(BR2_powerpc64)$(BR2_powerpc64le),
> +		$(call KCONFIG_ENABLE_OPT,CONFIG_PPC_DISABLE_WERROR,$(@D)/.config))
>  	$(if $(BR2_TARGET_ROOTFS_CPIO),
>  		$(call KCONFIG_ENABLE_OPT,CONFIG_BLK_DEV_INITRD,$(@D)/.config))
>  	# As the kernel gets compiled before root filesystems are
>