Hi Masahiro, I love your patch! Perhaps something to improve: [auto build test WARNING on masahiroy-kbuild/for-next] [also build test WARNING on masahiroy-kbuild/fixes linus/master v6.1-rc8 next-20221206] [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/Masahiro-Yamada/kbuild-move-Werror-from-KBUILD_CFLAGS-to-KBUILD_CPPFLAGS/20221206-120836 base: https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git for-next patch link: https://lore.kernel.org/r/20221206040731.442499-2-masahiroy%40kernel.org patch subject: [PATCH 2/2] kbuild: add -Wundef to KBUILD_CPPFLAGS for W=1 builds config: i386-defconfig compiler: gcc-11 (Debian 11.3.0-8) 11.3.0 reproduce (this is a W=1 build): # https://github.com/intel-lab-lkp/linux/commit/9c41976010ec03f9730df80eea55a21a79dda14a git remote add linux-review https://github.com/intel-lab-lkp/linux git fetch --no-tags linux-review Masahiro-Yamada/kbuild-move-Werror-from-KBUILD_CFLAGS-to-KBUILD_CPPFLAGS/20221206-120836 git checkout 9c41976010ec03f9730df80eea55a21a79dda14a # save the config file mkdir build_dir && cp config build_dir/.config make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash If you fix the issue, kindly add following tag where applicable | Reported-by: kernel test robot All warnings (new ones prefixed by >>): In file included from arch/x86/kernel/head_32.S:29: >> arch/x86/include/asm/pgtable_32.h:68:5: warning: "PTRS_PER_PMD" is not defined, evaluates to 0 [-Wundef] 68 | #if PTRS_PER_PMD > 1 | ^~~~~~~~~~~~ vim +/PTRS_PER_PMD +68 arch/x86/include/asm/pgtable_32.h ^1da177e4c3f41 include/asm-i386/pgtable.h Linus Torvalds 2005-04-16 58 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 59 /* ea3186b9572a1b arch/x86/include/asm/pgtable_32.h Arvind Sankar 2020-10-29 60 * This is used to calculate the .brk reservation for initial pagetables. ea3186b9572a1b arch/x86/include/asm/pgtable_32.h Arvind Sankar 2020-10-29 61 * Enough space is reserved to allocate pagetables sufficient to cover all ea3186b9572a1b arch/x86/include/asm/pgtable_32.h Arvind Sankar 2020-10-29 62 * of LOWMEM_PAGES, which is an upper bound on the size of the direct map of ea3186b9572a1b arch/x86/include/asm/pgtable_32.h Arvind Sankar 2020-10-29 63 * lowmem. 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 64 * ea3186b9572a1b arch/x86/include/asm/pgtable_32.h Arvind Sankar 2020-10-29 65 * With PAE paging (PTRS_PER_PMD > 1), we allocate PTRS_PER_PGD == 4 pages for ea3186b9572a1b arch/x86/include/asm/pgtable_32.h Arvind Sankar 2020-10-29 66 * the PMD's in addition to the pages required for the last level pagetables. 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 67 */ 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 @68 #if PTRS_PER_PMD > 1 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 69 #define PAGE_TABLE_SIZE(pages) (((pages) / PTRS_PER_PMD) + PTRS_PER_PGD) 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 70 #else 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 71 #define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD) 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 72 #endif 1e620f9b23e598 arch/x86/include/asm/pgtable_32.h Boris Ostrovsky 2016-12-08 73 -- 0-DAY CI Kernel Test Service https://01.org/lkp