linux-kernel - Re: [PATCH] Use CRC32 and a 1MiB dictionary for XZ compressed modules

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Date:   Fri, 22 Sep 2023 10:25:55 +0200
From:   Tor Vic <torvic9@...lbox.org>
To:     Martin Nybo Andersen <tweek@...ek.dk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Nick Terrell <terrelln@...com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Use CRC32 and a 1MiB dictionary for XZ compressed modules

> 
> Hello?

Hello,

> Anyone?
> 
> Best regards,
> - Martin
> 
> On Fri, 15 Sep 2023, Martin Nybo Andersen wrote:
> 
>> Kmod is now using the kernel decompressor which doesn't handle CRC64
>> and dictionaries larger than 1MiB.
>>
>> Fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1050582
>> Signed-off-by: Martin Nybo Andersen <tweek@...ek.dk>
>> ---
>> scripts/Makefile.modinst | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
>> index c59cc57286ba..ffbafbd3aeea 100644
>> --- a/scripts/Makefile.modinst
>> +++ b/scripts/Makefile.modinst
>> @@ -144,7 +144,7 @@ endif
>> quiet_cmd_gzip = GZIP    $@
>>       cmd_gzip = $(KGZIP) -n -f $<
>> quiet_cmd_xz = XZ      $@
>> -      cmd_xz = $(XZ) --lzma2=dict=2MiB -f $<
>> +      cmd_xz = $(XZ) --check=crc32 --lzma2=dict=1MiB -f $<

I wonder whether it should be guarded with
     ifdef CONFIG_MODULE_DECOMPRESS

But on the other hand, the difference between 1M and 2M is likely very 
small in terms of compression ratio.

Cheers,
Tor Vic

>> quiet_cmd_zstd = ZSTD    $@
>>       cmd_zstd = $(ZSTD) -T0 --rm -f -q $<
>>
>> -- 
>> 2.40.1
>>
>>
>