| Message ID | 20231002-disable-wformat-truncation-overflow-non-kprintf-v1-1-35179205c8d9@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: Disable clang's -Wformat-{overflow,truncation}-non-kprintf | expand |
On Mon, Oct 2, 2023 at 12:52 PM Nathan Chancellor <nathan@kernel.org> wrote: > > 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@kernel.org> This should be the final piece of the puzzle...a long arduous puzzle. Thanks Nathan! Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > --- > 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@kernel.org> > >
On Mon, Oct 02, 2023 at 12:52:28PM -0700, Nathan Chancellor wrote: > 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@kernel.org> > --- > 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@kernel.org> > I am going through my outstanding patches and I noticed this was not picked up. Masahiro, would you like me to resend it? It still applies cleanly to the current kbuild tree, although there will be a conflict in -next because of commit 89741e7e42f6 ("Makefile: Enable -Wstringop-overflow globally"), but there is not much that can be done about that. Cheers, Nathan
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)
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@kernel.org> --- scripts/Makefile.extrawarn | 7 +++++++ 1 file changed, 7 insertions(+) --- base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa change-id: 20231002-disable-wformat-truncation-overflow-non-kprintf-033e8d8b4de8 Best regards,