On Wed, 3 Aug 2016, Julien Grall wrote: > Hi Jan, > > On 03/08/16 09:53, Jan Beulich wrote: > > > > > On 02.08.16 at 20:43, <sstabell...@kernel.org> wrote: > > > On Tue, 2 Aug 2016, Jan Beulich wrote: > > > > > > > On 02.08.16 at 16:59, <andrew.coop...@citrix.com> wrote: > > > > > On 02/08/16 15:54, Jan Beulich wrote: > > > > > > > > > On 02.08.16 at 16:26, <julien.gr...@arm.com> wrote: > > > > > > > On 02/08/16 15:17, Jan Beulich wrote: > > > > > > > > Well, I find it quite odd for hypercall argument counts to > > > > > > > > differ > > > > > > > > between arches. I.e. I'd conclude the ABI was mis-specified. > > > > > > > Is it documented somewhere for the x86 code? Looking at Linux, the > > > > > > > privcmd call is only passing 5 arguments on both ARM and x86. > > > > > > arch-x86/xen-x86_32.h has > > > > > > > > > > > > * Hypercall interface: > > > > > > * Input: %ebx, %ecx, %edx, %esi, %edi, %ebp (arguments 1-6) > > > > > > * Output: %eax > > > > > > > > > > > > while arch-x86/xen-x86_64.h has > > > > > > > > > > > > * Hypercall interface: > > > > > > * Input: %rdi, %rsi, %rdx, %r10, %r8, %r9 (arguments 1-6) > > > > > > * Output: %rax > > > > > > > > > > The only actual 6 argument hypercall is the v4v hypercall, better > > > > > known > > > > > as __HYPERVISOR_xc_reserved_op at index 39, but that isn't implemented > > > > > anywhere upstream. > > > > > > > > But it serves as an example what now wouldn't work on ARM. > > > > > > At the time the arm hypercall ABI was published, it matched the x86 > > > hypercall ABI, which had only 5 hypercall arguments. > > > > > > The issue is that the x86 hypercall ABI changed, and now is out of sync > > > with ARM. The faulty commit being: > > > > That's one way of viewing it, but I don't think an appropriate one. > > 6-argument hypercalls had always been possible on x86, just that > > they might not have been documented in the public headers (but > > instead only in the actual hypercall implementation). > > I would tend to say that anything not documented in the public header is not > part of the ABI regardless how it has been implemented before hand.
I agree. What is documented (or not documented) in the public headers is the golden standard. > Anyway, I looked at the hypercall implementation on ARM and it seems that we > half support the 6th argument. For instance hypercall_create_continuation is > clobbering r5/x5 which is not part of the ABI. > > However do_trap_hypercall is only supporting up to 5 argument. > > I don't think it would be an issue to support 6 arguments on ARM. Stefano, > what do you think? I am OK with supporting 6 arguments hypercalls and it would be good to have both architectures match. The 32bit guest-side implementation needs special caring, but it should be OK (see HYPERCALL5 in Linux). Fortunately xen/include/public/arch-arm.h states that only arguments used by an hypercall can be clobbered. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
