On Fri, Feb 13, 2015 at 05:33:46PM +0000, Catalin Marinas wrote: > > > > The data structure definition is a little bit fragile, as it depends on > > > > user space not using the __BIT_ENDIAN symbol in a conflicting way. So > > > > far we have managed to keep that outside of general purpose headers, but > > > > it should at least blow up in an obvious way if it does, rather than > > > > breaking silently. > > > > > > > > I still think it's more practical to keep the zeroing in user space > > > > though. > > > > In that case, we keep defining __kernel_timespec64 with a 'typedef long > > > > long __kernel_snseconds_t', and it's up to the libc to either use > > > > __kernel_timespec64 as its timespec, or to define a C11-compliant > > > > timespec itself and zero out the bits before passing the data to the > > > > kernel. > > > > > > The problem with doing this in user space is syscall(2). If we don't > > > allow it, then it's fine to do the padding in libc. > > > > It's already the case that callers have to tiptoe around syscall(2) > > usage on a per-arch basis for silly things like the convention for > > passing 64-bit arguments on 32-bit archs, different arg orders to work > > around 64-bit alignment and issues with too many args, and various > > legacy issues. So I think manual use of syscall(2) is a less-critical > > issue, though of course from a libc perspective I would very much like > > for the kernel to handle it right. > > I think there is another problem with sign-extending tv_nsec in libc. > The prototype for functions like clock_settime(2) take a const struct > timespec *. There isn't anything to prevent such structure being in a > read-only section, even though it is unlikely. So libc would have to > duplicate the structure rather than just sign-extending tv_nsec in > place.
Yes, we already have to do this for x32 in musl. I'd rather not have to do the same for aarch64-ILP32. Rich -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
