On Fri, 2015-10-09 at 08:38 -0600, Jan Beulich wrote: > > > > On 09.10.15 at 14:46, <ian.campb...@citrix.com> wrote: > > On Fri, 2015-10-09 at 13:29 +0100, Andrew Cooper wrote: > > > On 09/10/15 09:25, Jan Beulich wrote: > > > > > > > On 09.10.15 at 04:56, <konrad.w...@oracle.com> wrote: > > > > > All existing commands ignore the parameter so this does > > > > > not break the ABI. > > > > Does it not? What about the debug mode clobbering of hypercall > > > > argument registers? > > > > > > That is an implementation detail of the hypervisor. It is irrelevant > > > to > > > guests whether Xen chooses to clobber the spare registers or not. > > > > Or in other words the effect here is to clobber one _less_ register, > > and > > the guest cannot have been relying on a register getting so clobbered > > (if > > nothing else it doesn't happen in debug=n builds). > > No, the one less register clobbered is in the first clobbering phase, > where _unused_ inputs get clobbered (for hypervisor internal > consumption). The second clobbering phase destroys all _used_ > input registers' contents (the guest visible values), and _this_ is > what results in ABI breakage (because callers assuming the > hypercall to take two arguments assume that the 3rd argument > register will retain its contents.
Ah, yes, that's correct. My mistake. Ian. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
