27 Jul
2012
27 Jul
'12
9 a.m.
On Thu, 2012-07-26 at 17:56 +0100, David Vrabel wrote:
On 26/07/12 16:33, Stefano Stabellini wrote:
- The hvc ISS is required to be 0xEA1, that is the Xen specific ARM
- hypercall tag.
Is this number, 0xea1, assigned to Xen by some external body?
The value and semantics of the hvc instructions immediate operand is entirely up to the hypervisor authors. We could have chosen 0 or some random number, we went for the latter because it increases the chances, by some tiny amount, that we won't clash with some other hypervisors ABI which makes supporting "foreign" guests that bit easier should it even come to it.
IOW it's arbitrary in the same way that a Linux system calls used to use int 0x80.
Ian.