APPLIED: [SRU jammy:linux-*-6.2] Revert variable symbol length modversion patch

[Stefan Bader]

On 27.06.23 11:45, Andrea Righi wrote:
> NOTE: this SRU doesn't have any patch, it explains a special action to
> do if you are cranking a Jammy kernel that is derived from Lunar.
> 
> [Impact]
> 
> In order to support Rust in the kernel starting with Lunar we had to
> apply the following UBUNTU SAUCE patch:
> 
>    27c4fe11712c ("UBUNTU: SAUCE: modpost: support arbitrary symbol length in modversion")
> 
> This patch can potentially introduce a user-space regression, because it
> alters how the module names are stored in the modversion_info area.
> Realistically it doesn't break anything, since this area is used only by
> the kmod tools (and they've been verified to work fine also with this
> change applied).
> 
> However, to be 100% that we don't introduce regressions it is safer to
> simply revert this patch, considering that we don't provide kernel Rust
> support in Jammy and without Rust this patch doesn't provide any
> benefit.
> 
> [Fix]
> 
> In order to fix this we need to explicitly revert the patch in all the
> Jammy kernels that are derived from any Lunar kernel.
> 
> To do so, after `cranky rebase`, run:
> 
>   git revert -s 27c4fe11712c
> 
> [ The sha1 should correspond to the proper patch to revert, otherwise
>    make sure that the patch "UBUNTU: SAUCE: modpost: support arbitrary
>    symbol length in modversion" is not applied, or it's already reverted ]
> 
> The comment for the revert should report something like this:
> ```
> 
>   Revert "UBUNTU: SAUCE: modpost: support arbitrary symbol length in modversion"
> 
>   This patch is required by Rust and it can potentially break user-space.
>   It is safer to revert this in all the kernel backported to old releases.
> ```
> 
> [Regression potential]
> 
> This revert is not very critical, realistically even with the variable
> modversions patch applied we won't regress any known tool, however we
> don't to risk to introduce potential user-space ABI changes. Fixing this
> requires a slightly different action, respect to our usual workflow, so
> if some kernels are shipped with the variable modversion patch (for any
> reason), we may experience regressions with kmod-related tools (e.g.,
> scripts that are using modinfo, modprobe and similar or custom tools
> that are parsing .ko sections directly).
> 

This should now be applied on all required branches.
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