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a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=cGxS198072jwnXqF9q4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: thyfOTUxfhtXwLCGw1ZYCipcOU86vrS9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzIzMDEyNiBTYWx0ZWRfXxWwQU2aCu7v6 aoxAwDvbu0bg9l/UJyadcZqd3jOa+MeehNCI7B0MDRink3KoGIY2VT89Yu1OS8ODmV37qN+rrb2 7cYbPNUP6rOlBuRCignLIubKCBkuyJryXXyCoNJhU0EIVVIZzTzErWa1zDdU5KNAQgAhg4JtoQw udcfM4JapKLEqCHomWrTEeoVUrkF48qBNyglrfC+OI/nxpMqdCoY6zl47J2V8Bc+iOn+nwVMPet lYE5GrMkKWLnSeJ4ZcLX+kGBUu7KE72ClJGqUYkyveETPLJvdLp/2rL/DdPXNDxpE256W/tWTq6 UMjRlspntRgLFMwZSjCn72KZCMm2p4vBZiNtJPsRtrN6xSPhXMykqffApjdUlC/8edaW4JJOsoo AeFKRffZg/91vx1qk//dfv5dTgnmj+PnE2UfA78zctScGbaMh7GZrOSA9jQhZOreJGtWJuFx On 7/22/25 9:28 PM, NeilBrown wrote: > 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. We might also want __attribute__((packed)) or even __attribute__((packed, aligned(4))). That still leaves undocumented the fact that the fields in the structure are treated as both endian types. In most other XDR functions we have been careful to write source code that shows where endianness changes or, conversely, where endianness is not consequential. > 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 > -- Chuck Lever