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SubjectRe: [PATCH v3 2/5] arm64: vdso32: Detect binutils support for dmb ishld
On Thu, Sep 26, 2019 at 10:43:39PM +0100, Vincenzo Frascino wrote:
> As reported by Will Deacon, older versions of binutils that do not
> support certain types of memory barriers can cause build failure of the
> vdso32 library.
>
> Add a compilation time mechanism that detects if binutils supports those
> instructions and configure the kernel accordingly.
>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> ---
> arch/arm64/include/asm/vdso/compat_barrier.h | 2 +-
> arch/arm64/kernel/vdso32/Makefile | 9 +++++++++
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/vdso/compat_barrier.h b/arch/arm64/include/asm/vdso/compat_barrier.h
> index fb60a88b5ed4..3fd8fd6d8fc2 100644
> --- a/arch/arm64/include/asm/vdso/compat_barrier.h
> +++ b/arch/arm64/include/asm/vdso/compat_barrier.h
> @@ -20,7 +20,7 @@
>
> #define dmb(option) __asm__ __volatile__ ("dmb " #option : : : "memory")
>
> -#if __LINUX_ARM_ARCH__ >= 8
> +#if __LINUX_ARM_ARCH__ >= 8 && defined(CONFIG_AS_DMB_ISHLD)
> #define aarch32_smp_mb() dmb(ish)
> #define aarch32_smp_rmb() dmb(ishld)
> #define aarch32_smp_wmb() dmb(ishst)
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index 19e0d3115ffe..77aa61340374 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -15,6 +15,8 @@ cc32-disable-warning = $(call try-run,\
> $(COMPATCC) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
> cc32-ldoption = $(call try-run,\
> $(COMPATCC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
> +cc32-as-instr = $(call try-run,\
> + printf "%b\n" "$(1)" | $(COMPATCC) $(VDSO_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3))

It's a shame that we have to duplicate the logic from scripts/Kbuild.include
here. Is there a way to reuse those helpers by temporarily overriding things
like CC and KBUILD_AFLAGS? If not, no bother, but thought I'd better ask.

Will

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