linux-kernel - Re: [PATCH v5 2/6] arm64: vdso32: Detect binutils support for dmb ishld

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Date:   Thu, 3 Oct 2019 13:18:16 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v5 2/6] arm64: vdso32: Detect binutils support for dmb ishld

On Thu, Oct 3, 2019 at 10:48 AM Vincenzo Frascino
<vincenzo.frascino@....com> wrote:
>
> Older versions of binutils that do not support certain types of memory
> barriers can cause build failure of the vdso32 library.

Do you know specific version numbers of binutils that are affected?
May be helpful to have in the commit message just for future
travelers.

>
> Add a compilation time mechanism that detects if binutils supports those
> instructions and configure the kernel accordingly.
>
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Reported-by: Will Deacon <will@...nel.org>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Tested-by: Catalin Marinas <catalin.marinas@....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))
>
>  # We cannot use the global flags to compile the vDSO files, the main reason
>  # being that the 32-bit compiler may be older than the main (64-bit) compiler
> @@ -53,6 +55,7 @@ endif
>  VDSO_CAFLAGS += -fPIC -fno-builtin -fno-stack-protector
>  VDSO_CAFLAGS += -DDISABLE_BRANCH_PROFILING
>
> +
>  # Try to compile for ARMv8. If the compiler is too old and doesn't support it,
>  # fall back to v7. There is no easy way to check for what architecture the code
>  # is being compiled, so define a macro specifying that (see arch/arm/Makefile).
> @@ -89,6 +92,12 @@ VDSO_CFLAGS += -Wno-int-to-pointer-cast
>  VDSO_AFLAGS := $(VDSO_CAFLAGS)
>  VDSO_AFLAGS += -D__ASSEMBLY__
>
> +# Check for binutils support for dmb ishld
> +dmbinstr := $(call cc32-as-instr,dmb ishld,-DCONFIG_AS_DMB_ISHLD=1)
> +
> +VDSO_CFLAGS += $(dmbinstr)
> +VDSO_AFLAGS += $(dmbinstr)
> +
>  VDSO_LDFLAGS := $(VDSO_CPPFLAGS)
>  # From arm vDSO Makefile
>  VDSO_LDFLAGS += -Wl,-Bsymbolic -Wl,--no-undefined -Wl,-soname=linux-vdso.so.1
> --
> 2.23.0
>


-- 
Thanks,
~Nick Desaulniers