smatch, __builtin_unreachable() and uninitialized var...

smatch, __builtin_unreachable() and uninitialized var...

[Toomas Soome]

hi!

While using smatch with OpenZFS code, we have stepped on this issue:

/home/runner/work/zfs/zfs/zfs/module/icp/algs/aes/aes_modes.c:90 aes_encrypt_contiguous_blocks() error: uninitialized symbol 'rv'.


The function is using conditional call to function, which return value is stored to rv and the “impossible” else leg is marked with __builtin_unreachable() as seen there:

https://github.com/openzfs/zfs/blob/master/module/icp/algs/aes/aes_modes.c#L77

it would be nice if smatch could use __builtin_unreachable() there to avoid this error…

thanks,
toomas

Re: smatch, __builtin_unreachable() and uninitialized var...

[Dan Carpenter]

On Mon, Nov 17, 2025 at 11:50:42AM +0200, Toomas Soome wrote:
> hi!
> 
> While using smatch with OpenZFS code, we have stepped on this issue:
> 
> /home/runner/work/zfs/zfs/zfs/module/icp/algs/aes/aes_modes.c:90 aes_encrypt_contiguous_blocks() error: uninitialized symbol 'rv'.
> 
> 
> The function is using conditional call to function, which return value is stored to rv and the “impossible” else leg is marked with __builtin_unreachable() as seen there:
> 
> https://github.com/openzfs/zfs/blob/master/module/icp/algs/aes/aes_modes.c#L77
> 
> it would be nice if smatch could use __builtin_unreachable() there to avoid this error…
> 

Huh.  Surprising that I've never noticed that before.  I have fixed this
locally and will push the change after testing it tonight.  (I emailed the
Sparse developers to see if they want to change it in their code as well,
but either way I will update Smatch).

Thanks for the bug report.

regards,
dan carpenter