Re: Build failure with trunk GCC 15 in fs/btrfs/print-tree.c (-Wunterminated-string-initialization)

[Sam James <sam@gentoo.org>]

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Alejandro Colomar <alx@kernel.org> writes:

> Hi Sam!
>
> On Thu, Jul 18, 2024 at 10:54:40PM GMT, Sam James wrote:
>> GCC 15 introduces a new warning -Wunterminated-string-initialization
>> which causes, with the kernel's -Werror=..., the following:
>> ```
>> /var/tmp/portage/sys-kernel/gentoo-kernel-6.6.41/work/linux-6.6/fs/btrfs/print-tree.c:29:49: error: initializer-string for array of ‘char’ is too long [-Werror=unterminated-string-initialization]
>>    29 |         { BTRFS_BLOCK_GROUP_TREE_OBJECTID,      "BLOCK_GROUP_TREE"      },
>>       |
>>       ^~~~~~~~~~~~~~~~~~
>> ```
>> 
>> It was introduced in https://gcc.gnu.org/PR115185. I don't have time
>> today to check the case to see what the best fix is, but CCing Alex who
>> wrote the warning implementation in case he has a chance.
>
> Thanks for forwarding the report.  It looks like a legit diagnostic.  It
> seems like a bug.

Thank you for analysing it so quickly! I normally try to for bug reports
but I'd already hit an unrelated kernel issue I was debugging so I
didn't want to worry about it for now.

> [...]

> The fix would be to add at least one byte to that array size.  Possibly
> make it 32 for alignment.  But I don't know if that array size is fixed
> by any ABI, so the maintainer will be better placed to find the suitable
> fix.
>
> The only alternatives I see are
>
> -  Use a larger number of elements for that array (1 would be enough).
> -  Use a shorter string so that it fits the 16 bytes.
>
> Have a lovely night!

You too :)

It might be worth making a list of "real bugs the warning found" as
stuff gets ported over the next few months.

> Alex

thanks,
sam

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