| Message ID | 20220316183833.1563139-1-arnd@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: fix clang warning about TRAMP_VALIAS | expand |
Hi Arnd, On 3/16/22 6:38 PM, 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] > return (char *)TRAMP_VALIAS + SZ_2K * slot; It is? Good to know! (clang 11 doesn't seem to be so fussy) Just for some more background: TRAMP_VALIAS existed before, but it wasn't defined if KPTI is disabled at compile time, you can't do that without CONFIG_EXPERT. I thought these dummy definitions would be cleaner than #ifdef'ing the code. > Change the addition to something clang does not complain about. Acked-by: James Morse <james.morse@arm.com> Thanks! James > 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); > >
On Wed, 16 Mar 2022 19:38:18 +0100, 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] > return (char *)TRAMP_VALIAS + SZ_2K * slot; > > [...] Applied to arm64 (for-next/fixes), thanks! [1/1] arm64: fix clang warning about TRAMP_VALIAS https://git.kernel.org/arm64/c/7f34b43e07cb
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? 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); >
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); > >
On Fri, Mar 18, 2022 at 12:52 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > 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 Fix should be landing shortly: https://reviews.llvm.org/D122224
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);