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To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jari Ruusu <jariruusu@protonmail.com>
Cc:     Sasha Levin <sashal@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        masahiroy@kernel.org
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From:   Jiri Slaby <jirislaby@kernel.org>
Subject: Re: Kernel version numbers after 4.9.255 and 4.4.255
Message-ID: <78ada91b-21ee-563f-9f75-3cbaeffafad4@kernel.org>
Date:   Thu, 4 Feb 2021 08:26:04 +0100
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On 04. 02. 21, 7:20, Greg Kroah-Hartman wrote:
> On Thu, Feb 04, 2021 at 05:59:42AM +0000, Jari Ruusu wrote:
>> Greg,
>> I hope that your linux kernel release scripts are
>> implemented in a way that understands that PATCHLEVEL= and
>> SUBLEVEL= numbers in top-level linux Makefile are encoded
>> as 8-bit numbers for LINUX_VERSION_CODE and
>> KERNEL_VERSION() macros, and must stay in range 0...255.
>> These 8-bit limits are hardcoded in both kernel source and
>> userspace ABI.
>>
>> After 4.9.255 and 4.4.255, your scripts should be
>> incrementing a number in EXTRAVERSION= in top-level
>> linux Makefile.
> 
> Should already be fixed in linux-next, right?

I assume you mean:
commit 537896fabed11f8d9788886d1aacdb977213c7b3
Author: Sasha Levin <sashal@kernel.org>
Date:   Mon Jan 18 14:54:53 2021 -0500

     kbuild: give the SUBLEVEL more room in KERNEL_VERSION

That would IMO break userspace as definition of kernel version has 
changed. And that one is UAPI/ABI (see 
include/generated/uapi/linux/version.h) as Jari writes. For example will 
glibc still work:
http://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/configure.ac;h=13abda0a51484c5951ffc6d718aa36b72f3a9429;hb=HEAD#l14

? Or gcc 10 (11 will have this differently):
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/bpf/bpf.c;hb=ee5c3db6c5b2c3332912fb4c9cfa2864569ebd9a#l165

and

https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/bpf/bpf-helpers.h;hb=ee5c3db6c5b2c3332912fb4c9cfa2864569ebd9a#l53

It might work somewhere, but there are a lot of (X * 65536 + Y * 256 + 
Z) assumptions all around the world. So this doesn't look like a good idea.

thanks,
-- 
js
suse labs