Hi Florian, On Thu, Nov 24, 2022 at 01:15:24PM +0100, Florian Weimer wrote: > * Jason A. Donenfeld: > > > Hi Florian, > > > > On Thu, Nov 24, 2022 at 06:25:39AM +0100, Florian Weimer wrote: > >> * Jason A. Donenfeld: > >> > >> > Hi Florian, > >> > > >> > On Wed, Nov 23, 2022 at 11:46:58AM +0100, Florian Weimer wrote: > >> >> * Jason A. Donenfeld: > >> >> > >> >> > + * The vgetrandom() function in userspace requires an opaque state, which this > >> >> > + * function provides to userspace, by mapping a certain number of special pages > >> >> > + * into the calling process. It takes a hint as to the number of opaque states > >> >> > + * desired, and returns the number of opaque states actually allocated, the > >> >> > + * size of each one in bytes, and the address of the first state. > >> >> > + */ > >> >> > +SYSCALL_DEFINE3(vgetrandom_alloc, unsigned long __user *, num, > >> >> > + unsigned long __user *, size_per_each, unsigned int, flags) > >> >> > >> >> I think you should make this __u64, so that you get a consistent > >> >> userspace interface on all architectures, without the need for compat > >> >> system calls. > >> > > >> > That would be quite unconventional. Most syscalls that take lengths do > >> > so with the native register size (`unsigned long`, `size_t`), rather > >> > than u64. If you can point to a recent trend away from this by > >> > indicating some commits that added new syscalls with u64, I'd be happy > >> > to be shown otherwise. But AFAIK, that's not the way it's done. > >> > >> See clone3 and struct clone_args. > > > > The struct is one thing. But actually, clone3 takes a `size_t`: > > > > SYSCALL_DEFINE2(clone3, struct clone_args __user *, uargs, size_t, size) > > > > I take from this that I too should use `size_t` rather than `unsigned > > long.` And it doesn't seem like there's any compat clone3. > > But vgetrandom_alloc does not use unsigned long, but unsigned long *. > You need to look at the contents for struct clone_args for comparison. Ah! I see what you mean; that's a good point. The usual register clearing thing isn't going to happen because these are addresses. I still am somewhat hesitant, though, because `size_t` is really the "proper" type to be used. Maybe the compat syscall thing is just a necessary evil? The other direction would be making this a u32, since 640k ought to be enough for anybody and such, but maybe that'd be a mistake too. So I'm not sure. Anybody else on the list with experience adding syscalls have an opinion? Jason
