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From: Ian Campbell <Ian.Campbell@citrix.com> Under Xen the toolstack is responsible for managing the domains in the system, e.g. creating, destroying, and otherwise manipulating them. To do this it uses a number of ioctls on the /proc/xen/privcmd device. Most of these (the MMAPBATCH ones) simply set things up such that a subsequenct mmap call will map the desired guest memory. Since valgrind has no way of knowing what the memory contains we assume that it is all initialised (to do otherwise would require valgrind to be observing the complete state of the system and not just the given process). The most interesting ioctl is XEN_IOCTL_PRIVCMD_HYPERCALL which allows the toolstack to make arbitrary hypercalls. Although the mechanism here is specific to the OS of the guest running the toolstack the hypercalls themselves are defined solely by the hypervisor. Therefore I have split support for this ioctl into a part in syswrap-linux.c which handles the ioctl itself and passes things onto a new syswrap-xen.c which handles the specifics of the hypercalls themselves. Porting this to another OS should just be a matter of wiring up syswrap-$OS.c to decode the ioctl and call into syswrap-xen.c. In the future we may want to split this into syswrap-$ARCH-xen.c but for now this is x86 only. The hypercall coverage here is pretty small but is enough to get reasonable(-ish) results out of the xl toolstack when listing, creating and destroying domains. One issue is that the hypercalls which are exlusively used by the toolstacks (as opposed to those used by guest operating systems) are not considered a stable ABI, since the hypervisor and the lowlevel tools are considered a matched pair. This covers the sysctl and domctl hypercalls which are a fairly large chunk of the support here. I'm not sure how to solve this without invoking a massive amount of duplication. Right now this targets the Xen unstable interface (which will shortly be released as Xen 4.2), perhaps I can get away with deferring this problem until the first change . On the plus side the vast majority of hypercalls are not of interest to the toolstack (they are used by guests) so we can get away without implementing them. Note: a hypercall only reads as many words from the ioctl arg struct as there are actual arguments to that hypercall and the toolstack only initialises the arguments which are used. However there is no space in the DEFN_PRE_TEMPLATE prototype to allow this to be communicated from syswrap-xen.c back to syswrap-linux.c. Since a hypercall can have at most 5 arguments I have hackily stolen ARG8 for this purpose. git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12963