linux-kernel - Re: [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections from bzImage

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Message-ID: <20200222050845.GA19912@ubuntu-m2-xlarge-x86>
Date:   Fri, 21 Feb 2020 22:08:45 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections
 from bzImage

On Thu, Jan 09, 2020 at 10:02:18AM -0500, Arvind Sankar wrote:
> Discarding the sections that are unused in the compressed kernel saves
> about 10 KiB on 32-bit and 6 KiB on 64-bit, mostly from .eh_frame.
> 
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
> ---
>  arch/x86/boot/compressed/vmlinux.lds.S | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
> index 508cfa6828c5..12a20603d92e 100644
> --- a/arch/x86/boot/compressed/vmlinux.lds.S
> +++ b/arch/x86/boot/compressed/vmlinux.lds.S
> @@ -73,4 +73,9 @@ SECTIONS
>  #endif
>  	. = ALIGN(PAGE_SIZE);	/* keep ZO size page aligned */
>  	_end = .;
> +
> +	/* Discard all remaining sections */
> +	/DISCARD/ : {
> +		*(*)
> +	}
>  }
> -- 
> 2.24.1
> 

This patch breaks linking with ld.lld:

$ make -j$(nproc) -s CC=clang LD=ld.lld O=out.x86_64 distclean defconfig bzImage
ld.lld: error: discarding .shstrtab section is not allowed
...

I am not exactly sure how to keep that section around (or if it is
ABSOLUTELY necessary like ld.lld seems to claim) otherwise I would send
a patch.

It would be nice not to break this tool since it is faster than ld.bfd.

Cheers,
Nathan