>>> On 07.02.19 at 10:04, <julien.gr...@arm.com> wrote: > On 2/7/19 6:32 AM, Christopher Clark wrote: >> It uses that null test because both are XEN_GUEST_HANDLE_PARAM type in >> the function signature: >> >> long do_argo_op( >> unsigned int cmd, >> XEN_GUEST_HANDLE_PARAM(void) arg1, >> XEN_GUEST_HANDLE_PARAM(void) arg2, >> unsigned long arg3, >> unsigned long arg4); >> >> and since it does that, the comment states NULL rather than zero. >> >> It is Xen's definition for NULL that is used, so the expected value in >> the register when the hypercall is invoked is: zero. > > As above, I don't think it is clearly define in the headers that NULL > means 0. This is rather an implicit written rules in the hope that every > OS are going to follow that. > > I know, I am pedantic here (hence the NIT) :). And I realize this is not > related to this series and a few places in the code assumes the same.
Exactly - just grep the public headers. The assumption is that a null handle is a type-wrapped representation of a NULL pointer. All platforms Xen runs on or has run on have NULL have a binary representation of zero afaik. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
