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Date:   Fri, 27 Mar 2020 12:55:22 +0000
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Amit Daniel Kachhap <amit.kachhap@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org,
        Will Deacon <will@kernel.org>,
        Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] arm64: Kconfig: ptrauth: Add binutils version check
 to fix mismatch
Message-ID: <20200327125522.GB18117@mbp>
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On Thu, Mar 26, 2020 at 09:02:00PM +0530, Amit Daniel Kachhap wrote:
> Recent addition of ARM64_PTR_AUTH exposed a mismatch issue with binutils.
> 9.1+ versions of gcc inserts a section note .note.gnu.property but this
> can be used properly by binutils version greater than 2.33.1. If older
> binutils are used then the following warnings are generated,
> 
> aarch64-linux-ld: warning: arch/arm64/kernel/vdso/vgettimeofday.o: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000
> aarch64-linux-objdump: warning: arch/arm64/lib/csum.o: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000
> aarch64-linux-nm: warning: .tmp_vmlinux1: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000
> 
> This patch enables ARM64_PTR_AUTH when gcc and binutils versions are
> compatible with each other. Older gcc which do not insert such section
> continue to work as before.
> 
> This scenario may not occur with clang as a recent commit 3b446c7d27ddd06
> ("arm64: Kconfig: verify binutils support for ARM64_PTR_AUTH") masks
> binutils version lesser then 2.34.
> 
> Reported-by: kbuild test robot <lkp@intel.com>
> Suggested-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
> ---
>  arch/arm64/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index e6712b6..73135da 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1503,7 +1503,7 @@ config ARM64_PTR_AUTH
>  	default y
>  	depends on !KVM || ARM64_VHE
>  	depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC
> -	depends on CC_IS_GCC || (CC_IS_CLANG && AS_HAS_CFI_NEGATE_RA_STATE)
> +	depends on (CC_IS_GCC && (GCC_VERSION < 90100 || LD_VERSION >= 233010000)) || (CC_IS_CLANG && AS_HAS_CFI_NEGATE_RA_STATE)

We should add some of the comments in the commit log to the Kconfig
entry. I would also split this in two (equivalent to CC_IS_ implies):

	depends on !CC_IS_GCC || GCC_VERSION < 90100 || LD_VERSION >= 233010000
	depends on !CC_IS_CLANG || AS_HAS_CFI_NEGATE_RA_STATE

and add a comment above the gcc/ld version checking.

(not entirely identical to the original if CC is neither of them but I
don't think we have this problem)

-- 
Catalin