Re: [PATCH v4 2/4] arch/x86: Move internal setup_data structures into setup_data.h

[Nathan Chancellor <nathan@kernel.org>]

On Tue, Jan 09, 2024 at 08:28:59AM +0800, kernel test robot wrote:
> Hi Thomas,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on tip/x86/core]
> [also build test WARNING on efi/next tip/master tip/auto-latest linus/master v6.7 next-20240108]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Thomas-Zimmermann/arch-x86-Move-UAPI-setup-structures-into-setup_data-h/20240108-180158
> base:   tip/x86/core
> patch link:    https://lore.kernel.org/r/20240108095903.8427-3-tzimmermann%40suse.de
> patch subject: [PATCH v4 2/4] arch/x86: Move internal setup_data structures into setup_data.h
> config: x86_64-rhel-8.3-bpf (https://download.01.org/0day-ci/archive/20240109/202401090800.UOBEKB3W-lkp@intel.com/config)
> compiler: ClangBuiltLinux clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240109/202401090800.UOBEKB3W-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202401090800.UOBEKB3W-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from arch/x86/realmode/rm/wakemain.c:3:
>    In file included from arch/x86/boot/boot.h:24:
>    In file included from arch/x86/include/asm/setup.h:10:
>    In file included from arch/x86/include/asm/page_types.h:7:
>    In file included from include/linux/mem_encrypt.h:17:
>    In file included from arch/x86/include/asm/mem_encrypt.h:18:
>    In file included from arch/x86/include/uapi/asm/bootparam.h:5:
> >> arch/x86/include/asm/setup_data.h:10:20: warning: field 'data' with variable sized type 'struct setup_data' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
>       10 |         struct setup_data data;
>          |                           ^
>    1 warning generated.

I think this warning is expected. This structure is now included in the
realmode part of arch/x86, which has its own set of build flags,
including -Wall, which includes -Wgnu on clang. The kernel obviously
uses GNU extensions and states this clearly with '-std=gnu11', so
-Wno-gnu is unconditionally added to KBUILD_CFLAGS for clang. It seems
that same treatment is needed for REALMODE_CFLAGS, which also matches
arch/x86/boot/compressed/Makefile, see commit 6c3b56b19730 ("x86/boot:
Disable Clang warnings about GNU extensions"):

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 1a068de12a56..24076db59783 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -53,6 +53,9 @@ REALMODE_CFLAGS += -fno-stack-protector
 REALMODE_CFLAGS += -Wno-address-of-packed-member
 REALMODE_CFLAGS += $(cc_stack_align4)
 REALMODE_CFLAGS += $(CLANG_FLAGS)
+ifdef CONFIG_CC_IS_CLANG
+REALMODE_CFLAGS += -Wno-gnu
+endif
 export REALMODE_CFLAGS
 
 # BITS is used as extension for files which are available in a 32 bit