From 258fafcd0683d9ccfa524129d489948ab3ddc24c Mon Sep 17 00:00:00 2001 From: Justin Stitt Date: Wed, 20 Jul 2022 16:23:32 -0700 Subject: Makefile.extrawarn: re-enable -Wformat for clang There's been an ongoing mission to re-enable the -Wformat warning for Clang. A previous attempt at enabling the warning showed that there were many instances of this warning throughout the codebase. The sheer amount of these warnings really polluted builds and thus -Wno-format was added to _temporarily_ toggle them off. After many patches the warning has largely been eradicated for x86, x86_64, arm, and arm64 on a variety of configs. The time to enable the warning has never been better as it seems for the first time we are ahead of them and can now solve them as they appear rather than tackling from a backlog. As to the root cause of this large backlog of warnings, Clang seems to pickup on some more nuanced cases of format warnings caused by implicit integer conversion as well as default argument promotions from printf-like functions. Link: https://github.com/ClangBuiltLinux/linux/issues/378 Suggested-by: Nick Desaulniers Signed-off-by: Justin Stitt Signed-off-by: Masahiro Yamada --- scripts/Makefile.extrawarn | 1 - 1 file changed, 1 deletion(-) (limited to 'scripts/Makefile.extrawarn') diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index f5f0d6f09053..9bbaf7112a9b 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -47,7 +47,6 @@ else ifdef CONFIG_CC_IS_CLANG KBUILD_CFLAGS += -Wno-initializer-overrides -KBUILD_CFLAGS += -Wno-format KBUILD_CFLAGS += -Wno-sign-compare KBUILD_CFLAGS += -Wno-format-zero-length KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast) -- cgit v1.2.3 From 21f9c8a13bb2a0c24d9c6b86bc0896542a28c197 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Thu, 11 Aug 2022 08:40:01 -0700 Subject: Revert "Makefile.extrawarn: re-enable -Wformat for clang" This reverts commit 258fafcd0683d9ccfa524129d489948ab3ddc24c. The clang -Wformat warning is terminally broken, and the clang people can't seem to get their act together. This test program causes a warning with clang: #include int main(int argc, char **argv) { printf("%hhu\n", 'a'); } resulting in t.c:5:19: warning: format specifies type 'unsigned char' but the argument has type 'int' [-Wformat] printf("%hhu\n", 'a'); ~~~~ ^~~ %d and apparently clang people consider that a feature, because they don't want to face the reality of how either C character constants, C arithmetic, and C varargs functions work. The rest of the world just shakes their head at that kind of incompetence, and turns off -Wformat for clang again. And no, the "you should use a pointless cast to shut this up" is not a valid answer. That warning should not exist in the first place, or at least be optinal with some "-Wformat-me-harder" kind of option. [ Admittedly, there's also very little reason to *ever* use '%hh[ud]' in C, but what little reason there is is entirely about 'I want to see only the low 8 bits of the argument'. So I would suggest nobody ever use that format in the first place, but if they do, the clang behavious is simply always wrong. Because '%hhu' takes an 'int'. It's that simple. ] Reported-by: Sudip Mukherjee (Codethink) Cc: Nick Desaulniers Signed-off-by: Linus Torvalds --- scripts/Makefile.extrawarn | 1 + 1 file changed, 1 insertion(+) (limited to 'scripts/Makefile.extrawarn') diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 9bbaf7112a9b..f5f0d6f09053 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -47,6 +47,7 @@ else ifdef CONFIG_CC_IS_CLANG KBUILD_CFLAGS += -Wno-initializer-overrides +KBUILD_CFLAGS += -Wno-format KBUILD_CFLAGS += -Wno-sign-compare KBUILD_CFLAGS += -Wno-format-zero-length KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast) -- cgit v1.2.3 From 370655bc183b1824ba623e621b58e8c2616c839c Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Wed, 10 Aug 2022 16:01:33 -0700 Subject: scripts/Makefile.extrawarn: Do not disable clang's -Wformat-zero-length There are no instances of this warning in the tree across several difference architectures and configurations. This was added by commit 26ea6bb1fef0 ("kbuild, LLVMLinux: Supress warnings unless W=1-3") back in 2014, where it might have been necessary, but there are no instances of it now so stop disabling it to increase warning coverage for clang. Signed-off-by: Nathan Chancellor Signed-off-by: Masahiro Yamada --- scripts/Makefile.extrawarn | 1 - 1 file changed, 1 deletion(-) (limited to 'scripts/Makefile.extrawarn') diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index f5f0d6f09053..0621c39a3955 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -49,7 +49,6 @@ ifdef CONFIG_CC_IS_CLANG KBUILD_CFLAGS += -Wno-initializer-overrides KBUILD_CFLAGS += -Wno-format KBUILD_CFLAGS += -Wno-sign-compare -KBUILD_CFLAGS += -Wno-format-zero-length KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast) KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access) -- cgit v1.2.3 From b0839b281c427e844143dba3893e25c83cdd6c17 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Thu, 1 Sep 2022 10:59:13 -0700 Subject: Makefile.extrawarn: re-enable -Wformat for clang; take 2 -Wformat was recently re-enabled for builds with clang, then quickly re-disabled, due to concerns stemming from the frequency of default argument promotion related warning instances. commit 258fafcd0683 ("Makefile.extrawarn: re-enable -Wformat for clang") commit 21f9c8a13bb2 ("Revert "Makefile.extrawarn: re-enable -Wformat for clang"") ISO WG14 has ratified N2562 to address default argument promotion explicitly for printf, as part of the upcoming ISO C2X standard. The behavior of clang was changed in clang-16 to not warn for the cited cases in all language modes. Add a version check, so that users of clang-16 now get the full effect of -Wformat. For older clang versions, re-enable flags under the -Wformat group that way users still get some useful checks related to format strings, without noisy default argument promotion warnings. I intentionally omitted -Wformat-y2k and -Wformat-security from being re-enabled, which are also part of -Wformat in clang-16. Link: https://github.com/ClangBuiltLinux/linux/issues/378 Link: https://github.com/llvm/llvm-project/issues/57102 Link: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2562.pdf Suggested-by: Justin Stitt Suggested-by: Nathan Chancellor Suggested-by: Youngmin Nam Signed-off-by: Nick Desaulniers Reviewed-by: Masahiro Yamada Reviewed-by: Nathan Chancellor Signed-off-by: Linus Torvalds --- scripts/Makefile.extrawarn | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'scripts/Makefile.extrawarn') diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 0621c39a3955..6ae482158bc4 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -47,7 +47,19 @@ else ifdef CONFIG_CC_IS_CLANG KBUILD_CFLAGS += -Wno-initializer-overrides +# Clang before clang-16 would warn on default argument promotions. +ifeq ($(shell [ $(CONFIG_CLANG_VERSION) -lt 160000 ] && echo y),y) +# Disable -Wformat KBUILD_CFLAGS += -Wno-format +# Then re-enable flags that were part of the -Wformat group that aren't +# problematic. +KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier +KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull +# Requires clang-12+. +ifeq ($(shell [ $(CONFIG_CLANG_VERSION) -ge 120000 ] && echo y),y) +KBUILD_CFLAGS += -Wformat-insufficient-args +endif +endif KBUILD_CFLAGS += -Wno-sign-compare KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast) KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare -- cgit v1.2.3