linux-kernel - Re: [PATCH] arm64/vdso: Remove --hash-style=sysv

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Message-ID: <a97e6b4232394e837666adbaf7e657900cb7b1a8.camel@xry111.site>
Date: Thu, 15 Aug 2024 03:55:54 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Fangrui Song <maskray@...gle.com>, Catalin Marinas
 <catalin.marinas@....com>,  Will Deacon <will@...nel.org>,
 linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] arm64/vdso: Remove --hash-style=sysv

On Thu, 2024-07-18 at 10:34 -0700, Fangrui Song wrote:
> glibc added support for .gnu.hash in 2006 and .hash has been obsoleted
> for more than one decade in many Linux distributions.  Using
> --hash-style=sysv might imply unaddressed issues and confuse readers.
> 
> Just drop the option and rely on the linker default, which is likely
> "both", or "gnu" when the distribution really wants to eliminate sysv
> hash overhead.
> 
> Similar to commit 6b7e26547fad ("x86/vdso: Emit a GNU hash").
> 
> Signed-off-by: Fangrui Song <maskray@...gle.com>

Hi Fangrui,

If I read tools/testing/selftests/vDSO/parse_vdso.c correctly, it does
know DT_GNU_HASH as at now.  Thus after this change the vDSO selftests
are skipped with "Couldn't find __vdso_gettimeofday" etc if the distro
enables --hash-style=gnu by default.

So it seems we need to add DT_GNU_HASH support for parse_vdso.c to keep
test coverage.

> ---
>  arch/arm64/kernel/vdso/Makefile   | 2 +-
>  arch/arm64/kernel/vdso32/Makefile | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index d63930c82839..d11da6461278 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -21,7 +21,7 @@ btildflags-$(CONFIG_ARM64_BTI_KERNEL) += -z force-bti
>  # potential future proofing if we end up with internal calls to the exported
>  # routines, as x86 does (see 6f121e548f83 ("x86, vdso: Reimplement vdso.so
>  # preparation in build-time C")).
> -ldflags-y := -shared -soname=linux-vdso.so.1 --hash-style=sysv	\
> +ldflags-y := -shared -soname=linux-vdso.so.1 \
>  	     -Bsymbolic --build-id=sha1 -n $(btildflags-y)
>  
>  ifdef CONFIG_LD_ORPHAN_WARN
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index cc4508c604b2..25a2cb6317f3 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -98,7 +98,7 @@ VDSO_AFLAGS += -D__ASSEMBLY__
>  # From arm vDSO Makefile
>  VDSO_LDFLAGS += -Bsymbolic --no-undefined -soname=linux-vdso.so.1
>  VDSO_LDFLAGS += -z max-page-size=4096 -z common-page-size=4096
> -VDSO_LDFLAGS += -shared --hash-style=sysv --build-id=sha1
> +VDSO_LDFLAGS += -shared --build-id=sha1
>  VDSO_LDFLAGS += --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
>  
>  

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University