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SubjectRe: [PATCH v3 2/5] arm64: vdso32: Detect binutils support for dmb ishld
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On 10/1/19 2:26 PM, Will Deacon wrote:
> 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.
>

I tried to define a rule in scripts/Kbuild.include at the beginning doing what
you are saying but I could not end up with a working solution, hence I ended up
with a dedicated one.

> Will
>

--
Regards,
Vincenzo

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