linux-kernel - Re: [PATCH v2 mips-next 2/4] MIPS: vmlinux.lds.S: add ".gnu.attributes" to DISCARDS

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Message-ID: <202101061400.8F83981AE@keescook>
Date:   Wed, 6 Jan 2021 14:07:07 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Alexander Lobakin <alobakin@...me>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Alex Smith <alex.smith@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Markos Chandras <markos.chandras@...tec.com>,
        linux-mips@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 mips-next 2/4] MIPS: vmlinux.lds.S: add
 ".gnu.attributes" to DISCARDS

On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:
> Discard GNU attributes at link time as kernel doesn't use it at all.
> Solves a dozen of the following ld warnings (one per every file):
> 
> mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes'
> from `arch/mips/kernel/head.o' being placed in section
> `.gnu.attributes'
> mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes'
> from `init/main.o' being placed in section `.gnu.attributes'
> 
> Misc: sort DISCARDS section entries alphabetically.

Hmm, I wonder what is causing the appearance of .eh_frame? With help I
tracked down all the causes of this on x86, arm, and arm64, so that's
why it's not in the asm-generic DISCARDS section. I suspect this could
be cleaned up for mips too?

Similarly for .gnu.attributes. What is generating that? (Or, more
specifically, why is it both being generated AND discarded?)

-Kees

> 
> Signed-off-by: Alexander Lobakin <alobakin@...me>
> ---
>  arch/mips/kernel/vmlinux.lds.S | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
> index 83e27a181206..5d6563970ab2 100644
> --- a/arch/mips/kernel/vmlinux.lds.S
> +++ b/arch/mips/kernel/vmlinux.lds.S
> @@ -221,9 +221,10 @@ SECTIONS
>  		/* ABI crap starts here */
>  		*(.MIPS.abiflags)
>  		*(.MIPS.options)
> +		*(.eh_frame)
> +		*(.gnu.attributes)
>  		*(.options)
>  		*(.pdr)
>  		*(.reginfo)
> -		*(.eh_frame)
>  	}
>  }
> -- 
> 2.30.0
> 
> 

-- 
Kees Cook