Recently, clang added support for -Wformat-overflow and -Wformat-truncation. When building the kernel, it was discovered that clang's implementation of these warnings handles the '%p' specifier, which differs from GCC's implementation. This results in false positive warnings due to the kernel's various '%p' extensions. Fortunately, the clang developers placed this warning difference into a separate flag, allowing the kernel to turn off the warning for '%p' unconditionally. This is not currently an issue for a normal build, as -Wformat-overflow and -Wformat-truncation are unconditionally disabled, which includes this sub-warning. However, ever since commit 6d4ab2e97dcf ("extrawarn: enable format and stringop overflow warnings in W=1"), these warnings are in W=1 and the goal is to enable them in the normal build once they are all eliminated. Disable the warnings for W=1 to avoid false positives. This block should move with -Wformat-overflow and -Wformat-truncation when they are enabled for a normal build. Link: https://github.com/ClangBuiltLinux/linux/issues/1923 Link: https://github.com/llvm/llvm-project/issues/64871 Link: https://github.com/llvm/llvm-project/pull/65969 Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219 Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78512 Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> --- scripts/Makefile.extrawarn | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 2fe6f2828d37..bad1baa2cfb4 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -106,6 +106,13 @@ KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable) KBUILD_CFLAGS += $(call cc-option, -Wpacked-not-aligned) KBUILD_CFLAGS += $(call cc-option, -Wformat-overflow) KBUILD_CFLAGS += $(call cc-option, -Wformat-truncation) +# Clang checks for overflow/truncation with '%p', while GCC does not: +# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219 +# The kernel has many extensions to '%p' that clang does not understand, so +# always disable these warnings when '-Wformat-truncation' and +# '-Wformat-overflow' are enabled. +KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf) +KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf) KBUILD_CFLAGS += $(call cc-option, -Wstringop-overflow) KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation) --- base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa change-id: 20231002-disable-wformat-truncation-overflow-non-kprintf-033e8d8b4de8 Best regards, -- Nathan Chancellor <nathan@xxxxxxxxxx>