Re: [PATCH 01/12] kbuild: make -Woverride-init warnings more consistent

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 26 Mar 2024, Arnd Bergmann <arnd@kernel.org> wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> The -Woverride-init warn about code that may be intentional or not,
> but the inintentional ones tend to be real bugs, so there is a bit of
> disagreement on whether this warning option should be enabled by default
> and we have multiple settings in scripts/Makefile.extrawarn as well as
> individual subsystems.
>
> Older versions of clang only supported -Wno-initializer-overrides with
> the same meaning as gcc's -Woverride-init, though all supported versions
> now work with both. Because of this difference, an earlier cleanup of
> mine accidentally turned the clang warning off for W=1 builds and only
> left it on for W=2, while it's still enabled for gcc with W=1.
>
> There is also one driver that only turns the warning off for newer
> versions of gcc but not other compilers, and some but not all the
> Makefiles still use a cc-disable-warning conditional that is no
> longer needed with supported compilers here.
>
> Address all of the above by removing the special cases for clang
> and always turning the warning off unconditionally where it got
> in the way, using the syntax that is supported by both compilers.
>
> Fixes: 2cd3271b7a31 ("kbuild: avoid duplicate warning options")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpu/drm/amd/display/dc/dce110/Makefile |  2 +-
>  drivers/gpu/drm/amd/display/dc/dce112/Makefile |  2 +-
>  drivers/gpu/drm/amd/display/dc/dce120/Makefile |  2 +-
>  drivers/gpu/drm/amd/display/dc/dce60/Makefile  |  2 +-
>  drivers/gpu/drm/amd/display/dc/dce80/Makefile  |  2 +-
>  drivers/gpu/drm/i915/Makefile                  |  6 +++---
>  drivers/gpu/drm/xe/Makefile                    |  4 ++--
>  drivers/net/ethernet/renesas/sh_eth.c          |  2 +-
>  drivers/pinctrl/aspeed/Makefile                |  2 +-
>  fs/proc/Makefile                               |  2 +-
>  kernel/bpf/Makefile                            |  2 +-
>  mm/Makefile                                    |  3 +--
>  scripts/Makefile.extrawarn                     | 10 +++-------
>  13 files changed, 18 insertions(+), 23 deletions(-)
>

[snip]

> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index 3ef6ed41e62b..4c2f85632391 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -33,9 +33,9 @@ endif
>  subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror
>  
>  # Fine grained warnings disable
> -CFLAGS_i915_pci.o = $(call cc-disable-warning, override-init)
> -CFLAGS_display/intel_display_device.o = $(call cc-disable-warning, override-init)
> -CFLAGS_display/intel_fbdev.o = $(call cc-disable-warning, override-init)
> +CFLAGS_i915_pci.o = -Wno-override-init
> +CFLAGS_display/intel_display_device.o = -Wno-override-init
> +CFLAGS_display/intel_fbdev.o = -Wno-override-init
>  
>  # Support compiling the display code separately for both i915 and xe
>  # drivers. Define I915 when building i915.
> diff --git a/drivers/gpu/drm/xe/Makefile b/drivers/gpu/drm/xe/Makefile
> index 5a428ca00f10..c29a850859ad 100644
> --- a/drivers/gpu/drm/xe/Makefile
> +++ b/drivers/gpu/drm/xe/Makefile
> @@ -172,8 +172,8 @@ subdir-ccflags-$(CONFIG_DRM_XE_DISPLAY) += \
>  	-Ddrm_i915_gem_object=xe_bo \
>  	-Ddrm_i915_private=xe_device
>  
> -CFLAGS_i915-display/intel_fbdev.o = $(call cc-disable-warning, override-init)
> -CFLAGS_i915-display/intel_display_device.o = $(call cc-disable-warning, override-init)
> +CFLAGS_i915-display/intel_fbdev.o = -Wno-override-init
> +CFLAGS_i915-display/intel_display_device.o = -Wno-override-init

For i915 and xe parts,

Acked-by: Jani Nikula <jani.nikula@intel.com>

>  # Rule to build SOC code shared with i915
>  $(obj)/i915-soc/%.o: $(srctree)/drivers/gpu/drm/i915/soc/%.c FORCE
> diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
> index 475e1e8c1d35..0786eb0da391 100644
> --- a/drivers/net/ethernet/renesas/sh_eth.c
> +++ b/drivers/net/ethernet/renesas/sh_eth.c
> @@ -50,7 +50,7 @@
>   * the macros available to do this only define GCC 8.
>   */
>  __diag_push();
> -__diag_ignore(GCC, 8, "-Woverride-init",
> +__diag_ignore_all("-Woverride-init",
>  	      "logic to initialize all and then override some is OK");

This is nice because it's more localized than the per-file
disable. However, we tried to do this in i915, but this doesn't work for
GCC versions < 8, and some defconfigs enabling -Werror forced us to
revert. See commit 290d16104575 ("Revert "drm/i915: use localized
__diag_ignore_all() instead of per file"").

BR,
Jani.


-- 
Jani Nikula, Intel