Messages in this thread Patch in this message | | | From | Nick Desaulniers <> | Date | Fri, 18 Mar 2022 12:52:18 -0700 | Subject | Re: [PATCH] arm64: fix clang warning about TRAMP_VALIAS |
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On Fri, Mar 18, 2022 at 12:11 PM Robin Murphy <robin.murphy@arm.com> wrote: > > On 2022-03-16 18:38, Arnd Bergmann wrote: > > From: Arnd Bergmann <arnd@arndb.de> > > > > The newly introduced TRAMP_VALIAS definition causes a build warning > > with clang-14: > > > > arch/arm64/include/asm/vectors.h:66:31: error: arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension [-Werror,-Wnull-pointer-arithmetic] > > Tangentially, all the other GNU extensions we depend on throughout Linux > are also GNU extensions. Do we know what's special about this one?
My first thought is that -Wnull-pointer-arithmetic should be in the -Wgnu flag group, such that -Wno-gnu (as set by Kbuild) implies -Wno-null-pointer-arithmetic.
One issue seems to be that -Wnull-pointer-arithmetic seems to control at least 2 different checks in clang.
https://godbolt.org/z/hdYYejj3d
So it's likely these two checks should have 2 distinct flags, such that the warning we're observing can be grouped under -Wgnu.
Filed: https://github.com/llvm/llvm-project/issues/54444
> > Robin. > > > return (char *)TRAMP_VALIAS + SZ_2K * slot; > > > > Change the addition to something clang does not complain about. > > > > Fixes: bd09128d16fa ("arm64: Add percpu vectors for EL1") > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > --- > > arch/arm64/include/asm/vectors.h | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > I see this warning on 5.17-rc8, but did not test it on linux-next, > > which may already have a fix. > > > > diff --git a/arch/arm64/include/asm/vectors.h b/arch/arm64/include/asm/vectors.h > > index f64613a96d53..bc9a2145f419 100644 > > --- a/arch/arm64/include/asm/vectors.h > > +++ b/arch/arm64/include/asm/vectors.h > > @@ -56,14 +56,14 @@ enum arm64_bp_harden_el1_vectors { > > DECLARE_PER_CPU_READ_MOSTLY(const char *, this_cpu_vector); > > > > #ifndef CONFIG_UNMAP_KERNEL_AT_EL0 > > -#define TRAMP_VALIAS 0 > > +#define TRAMP_VALIAS 0ul > > #endif > > > > static inline const char * > > arm64_get_bp_hardening_vector(enum arm64_bp_harden_el1_vectors slot) > > { > > if (arm64_kernel_unmapped_at_el0()) > > - return (char *)TRAMP_VALIAS + SZ_2K * slot; > > + return (char *)(TRAMP_VALIAS + SZ_2K * slot); > > > > WARN_ON_ONCE(slot == EL1_VECTOR_KPTI); > >
-- Thanks, ~Nick Desaulniers
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