Re: [PATCH rc 4/4] iommufd/selftest: Fix build warnings due to uninitialized mfd

[Jason Gunthorpe]

On Sun, Jun 15, 2025 at 10:02:06PM -0700, Nicolin Chen wrote:
> Commit 869c788909b9 ("selftests: harness: Stop using setjmp()/longjmp()")
> changed the harness structure. For some unknown reason, two build warnings
> occur to the iommufd selftest:
> 
> iommufd.c: In function ‘wrapper_iommufd_mock_domain_all_aligns’:
> iommufd.c:1807:17: warning: ‘mfd’ may be used uninitialized in this function
>  1807 |                 close(mfd);
>       |                 ^~~~~~~~~~
> iommufd.c:1767:13: note: ‘mfd’ was declared here
>  1767 |         int mfd;
>       |             ^~~
> iommufd.c: In function ‘wrapper_iommufd_mock_domain_all_aligns_copy’:
> iommufd.c:1870:17: warning: ‘mfd’ may be used uninitialized in this function
>  1870 |                 close(mfd);
>       |                 ^~~~~~~~~~
> iommufd.c:1819:13: note: ‘mfd’ was declared here
>  1819 |         int mfd;
>       |             ^~~
> 
> All the mfd have been used in the variant->file path only, so it's likely
> a false alarm.
> 
> FWIW, the commit mentioned above does not cause this, yet it might affect
> gcc in a certain way that resulted in the warnings. It is also found that
> ading a dummy setjmp (which doesn't make sense) could mute the warnings:
> https://lore.kernel.org/all/aEi8DV+ReF3v3Rlf@xxxxxxxxxx/
> 
> The job of this selftest is to catch kernel bug, while such warnings will
> unlikely disrupt its role. Mute the warning by force initializing the mfd
> and add an ASSERT_GT().
> 
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> ---
>  tools/testing/selftests/iommu/iommufd.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason