On 8/29/22 13:09, Sathyanarayanan Kuppuswamy wrote: > With the changed format, we avoided the holes, but it still adds 7 bytes of padding. > > Total size of struct is 32 bytes. > > struct tdx_report_req { > __u64 reportdata; /* 0 8 */ > __u64 tdreport; /* 8 8 */ > __u32 rpd_len; /* 16 4 */ > __u32 tdr_len; /* 20 4 */ > __u8 subtype; /* 24 1 */ > > /* size: 32, cachelines: 1, members: 5 */ > /* padding: 7 */ > /* last cacheline: 32 bytes */ > }; Might as well make some use of the padding and add: u8 reserved[7]; That will ensure that the entire structure is explicitly sized *AND* leave you room to add flags or other fun in the future without a new ABI.