* Catalin Marinas: > On Tue, Dec 11, 2018 at 10:02:45AM +0100, Arnd Bergmann wrote: >> On Tue, Dec 11, 2018 at 6:35 AM Andy Lutomirski <luto@xxxxxxxxxx> wrote: >> > I tried to understand what's going on. As far as I can tell, most of >> > the magic is the fact that __kernel_long_t and __kernel_ulong_t are >> > 64-bit as seen by x32 user code. This means that a decent number of >> > uapi structures are the same on x32 and x86_64. Syscalls that only >> > use structures like this should route to the x86_64 entry points. But >> > the implementation is still highly dubious -- in_compat_syscall() will >> > be *true* in such system calls, >> >> I think the fundamental issue was that the intention had always been >> to use only the 64-bit entry points for system calls, but the most >> complex one we have -- ioctl() -- has to use the compat entry point >> because device drivers define their own data structures using 'long' >> and pointer members and they need translation, as well as >> matching in_compat_syscall() checks. This in turn breaks down >> again whenever a driver defines an ioctl command that takes >> a __kernel_long_t or a derived type like timespec as its argument. > > With arm64 ILP32 we tried to avoid the ioctl() problem by having > __kernel_long_t 32-bit, IOW mimicking the arm32 ABI (compat). The > biggest pain point is signals where the state is completely different > from arm32 (more, wider registers) and can't be dealt with by the compat > layer. I would expect to approach this from the opposite direction: use 64-bit types in places where the 64-bit kernel interface uses 64-bit types. After all, not everyone who is interested in ILP32 has a companion 32-bit architecture which could serve as a model for the application ABI. (If there are conflicts with POSIX, then POSIX needs to be fixed to support this.) Thanks, Florian
