GCC gets a bit confused and reports:

In function '_test_cmd_get_hw_info', inlined from 'iommufd_ioas_get_hw_info' at iommufd.c:779:3, inlined from 'wrapper_iommufd_ioas_get_hw_info' at iommufd.c:752:1:

...

iommufd_utils.h:804:37: warning: array subscript 'struct iommu_test_hw_info[0]' is partly outside array bounds of 'struct iommu_test_hw_info_buffer_smaller[1]' [-Warray-bounds=]

804 | assert(!info->flags); | ~~~~^~~~~~~ iommufd.c: In function 'wrapper_iommufd_ioas_get_hw_info': iommufd.c:761:11: note: object 'buffer_smaller' of size 4 761 | } buffer_smaller; | ^~~~~~~~~~~~~~

While it is true that "struct iommu_test_hw_info[0]" is partly out of bounds of the input pointer, it is not true that info->flags is out of bounds. Unclear why it warns on this.

Reuse an existing properly sized stack buffer and pass a truncated length instead to test the same thing.

Fixes: af4fde93c319 ("iommufd/selftest: Add coverage for IOMMU_GET_HW_INFO ioctl") Reported-by: kernel test robot lkp@intel.com Closes: https://lore.kernel.org/oe-kbuild-all/202512032344.kaAcKFIM-lkp@intel.com/ Signed-off-by: Jason Gunthorpe jgg@nvidia.com --- tools/testing/selftests/iommu/iommufd.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/iommu/iommufd.c b/tools/testing/selftests/iommu/iommufd.c index 10e051b6f592df..dadad277f4eb2e 100644 --- a/tools/testing/selftests/iommu/iommufd.c +++ b/tools/testing/selftests/iommu/iommufd.c @@ -755,9 +755,6 @@ TEST_F(iommufd_ioas, get_hw_info) struct iommu_test_hw_info info; uint64_t trailing_bytes; } buffer_larger; - struct iommu_test_hw_info_buffer_smaller { - __u32 flags; - } buffer_smaller;

if (self->device_id) { uint8_t max_pasid = 0; @@ -789,8 +786,9 @@ TEST_F(iommufd_ioas, get_hw_info) * the fields within the size range still gets updated. */ test_cmd_get_hw_info(self->device_id, - IOMMU_HW_INFO_TYPE_DEFAULT, - &buffer_smaller, sizeof(buffer_smaller)); + IOMMU_HW_INFO_TYPE_DEFAULT, &buffer_exact, + offsetofend(struct iommu_test_hw_info, + flags)); test_cmd_get_hw_info_pasid(self->device_id, &max_pasid); ASSERT_EQ(0, max_pasid); if (variant->pasid_capable) {

base-commit: 93013488dd77dd2ea8bd23355a5587d9e6dac185