linux-kernel - Re: [PATCH v6 4/8] init: add support for zstd compressed kernel

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Date:   Tue, 7 Jul 2020 18:11:30 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Nick Terrell <nickrterrell@...il.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Chris Mason <clm@...com>,
        linux-kbuild@...r.kernel.org, x86@...nel.org,
        gregkh@...uxfoundation.org, Petr Malat <oss@...at.biz>,
        Kees Cook <keescook@...omium.org>,
        Kernel Team <Kernel-team@...com>,
        Adam Borowski <kilobyte@...band.pl>,
        Patrick Williams <patrickw3@...com>, rmikey@...com,
        mingo@...nel.org, Patrick Williams <patrick@...cx.xyz>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Norbert Lange <nolange79@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Terrell <terrelln@...com>
Subject: Re: [PATCH v6 4/8] init: add support for zstd compressed kernel

On Mon, Jul 06, 2020 at 08:46:00PM -0700, Nick Terrell wrote:
> From: Nick Terrell <terrelln@...com>
> 
> * Adds the zstd cmd to scripts/Makefile.lib
> * Adds the HAVE_KERNEL_ZSTD and KERNEL_ZSTD options
> 
> Architecture specific support is still needed for decompression.
> 
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 916b2f7f7098..d960f8815f87 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -413,6 +413,21 @@ quiet_cmd_xzkern = XZKERN  $@
>  quiet_cmd_xzmisc = XZMISC  $@
>        cmd_xzmisc = cat $(real-prereqs) | $(XZ) --check=crc32 --lzma2=dict=1MiB > $@
>  
> +# ZSTD
> +# ---------------------------------------------------------------------------
> +# Appends the uncompressed size of the data using size_append. The .zst
> +# format has the size information available at the beginning of the file too,
> +# but it's in a more complex format and it's good to avoid changing the part
> +# of the boot code that reads the uncompressed size.
> +# Note that the bytes added by size_append will make the zstd tool think that
> +# the file is corrupt. This is expected.
> +
> +quiet_cmd_zstd = ZSTD    $@
> +cmd_zstd = (cat $(filter-out FORCE,$^) | \
		   ^^ should just be $(real-prereqs)
> +	zstd -19 && \
> +        $(call size_append, $(filter-out FORCE,$^))) > $@ || \
	   ^^ size_append does not take arguments. It's used as just
	   $(size_append) and will always output shell code to print the
	   total size of $(real-prereqs) -- see other compressor command
	   definitions.
> +	(rm -f $@ ; false)
> +
>  # ASM offsets
>  # ---------------------------------------------------------------------------
>  
> -- 
> 2.27.0
>