Re: Possible build time regression affecting stable kernels

[Luiz Capitulino <luizcap@amazon.com>]

On 2023-06-01 09:20, Greg KH wrote:

> 
> 
> 
> On Thu, Jun 01, 2023 at 09:13:21AM -0400, Luiz Capitulino wrote:
>>
>>
>> On 2023-06-01 02:06, Greg KH wrote:
>>
>>>
>>>
>>>
>>> On Wed, May 31, 2023 at 10:12:40PM -0400, Luiz Capitulino wrote:
>>>> Hi Paul,
>>>>
>>>> A number of stable kernels recently backported this upstream commit:
>>>>
>>>> """
>>>> commit 4ce1f694eb5d8ca607fed8542d32a33b4f1217a5
>>>> Author: Paul Moore <paul@paul-moore.com>
>>>> Date:   Wed Apr 12 13:29:11 2023 -0400
>>>>
>>>>       selinux: ensure av_permissions.h is built when needed
>>>> """
>>>>
>>>> We're seeing a build issue with this commit where the "crash" tool will fail
>>>> to start, it complains that the vmlinux image and /proc/version don't match.
>>>>
>>>> A minimum reproducer would be having "make" version before 4.3 and building
>>>> the kernel with:
>>>>
>>>> $ make bzImages
>>>> $ make modules
>>>>
>>>> Then compare the version strings in the bzImage and vmlinux images,
>>>> we can use "strings" for this. For example, in the 5.10.181 kernel I get:
>>>>
>>>> $ strings vmlinux | egrep '^Linux version'
>>>> Linux version 5.10.181 (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #2 SMP Thu Jun 1 01:26:38 UTC 2023
>>>>
>>>> $ strings ./arch/x86_64/boot/bzImage | egrep 'ld version'
>>>> 5.10.181 (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #1 SMP Thu Jun 1 01:23:59 UTC 2023
>>>>
>>>> The version string in the bzImage doesn't have the "Linux version" part, but
>>>> I think this is added by the kernel when printing. If you compare the strings,
>>>> you'll see that they have a different build date and the "#1" and "#2" are
>>>> different.
>>>>
>>>> This only happens with commit 4ce1f694eb5 applied and older "make", in my case I
>>>> have "make" version 3.82.
>>>>
>>>> If I revert 4ce1f694eb5 or use "make" version 4.3 I get identical strings (except
>>>> for the "Linux version" part):
>>>>
>>>> $ strings vmlinux | egrep '^Linux version'
>>>> Linux version 5.10.181+ (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #1 SMP Thu Jun 1 01:29:11 UTC 2023
>>>>
>>>> $ strings ./arch/x86_64/boot/bzImage | egrep 'ld version'
>>>> 5.10.181+ (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #1 SMP Thu Jun 1 01:29:11 UTC 2023
>>>>
>>>> Maybe the grouped target usage in 4ce1f694eb5 with older "make" is causing a
>>>> rebuild of the vmlinux image in "make modules"? If yes, is this expected?
>>>>
>>>> I'm afraid this issue could be high impact for distros with older user-space.
>>>
>>> Is this issue also in 6.4-rc1 where this change came from?
>>
>> Yes. I'm reporting this here because I'm more concerned with -stable kernels since
>> they're more likely to be running on older user-space.
> 
> Yeah, we are bug-compatible!  :)
> 
> When this gets fixed in Linus's tree, I'll be glad to backport the
> changes to the other kernels.  Please work with the developers to get
> that fixed there.

OK, I'll report it there, but shouldn't we avoid regressing -stable kernels?

- Luiz