On Wed, 23 Jul 2025, Chuck Lever wrote: > On 7/22/25 1:36 AM, Christoph Hellwig wrote: > > On Mon, Jul 21, 2025 at 05:48:55PM +0300, Sergey Bashirov wrote: > >> Compilers may optimize the layout of C structures, > > > > By interpreting the standard in the most hostile way: yes. > > In practice: no. > > Earnest question: Is NFSD/XDR properly insulated against the "randomize > structure layout" option? > > > > Just about every file system on-disk format and every network wire > > protocol depends on the compiler not "optimizing" properly padded > > C structures. > It's an intrinsic assumption that is not documented in the code or > anywhere else. IMO that is a latent banana peel. We could document it in the code with __no_randomize_layout after the structure definition. But currently the only structures that are randomized in Linux are those which are entirely function pointers, and those marked __randomize_layout. (See documentation for "RANDSTRUCT_FULL") > > While not urgent, this is a defensive change and it improves code > portability amongst compilers and languages (eg, Rust). > I'm neither for nor against the change. I would be interested to know how much it changes the code side (if at all). NeilBrown
