Re: [Xen-devel] Passing pointers to hypercalls

["Amaro, Emmanuel" <amaro@xxxxxxxxxx>]

Of course. Agh, I forgot to change it to 1.

If someone else looks at this, in my case it means this file: xen/arch/x86/x86_64/entry.S

Thanks!

On Nov 9, 2014, at 2:27 PM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

On 09/11/14 19:16, Amaro, Emmanuel wrote:

Hello,

I am trying to pass a pointer to an hyper call in the simplest possible way, set it’s value, an return it to the guest.

I have tried 2 different ways:

- Directly with simple pointers (I read somewhere this would work on x86), but the pointer address is set to 0x0000deadbeef, so dereferencing it causes a panic.

- With XEN_GUEST_HANDLE:

long do_dummy(XEN_GUEST_HANDLE(uint64_t) ptr)

{

It looks like you have introduced a new hypercall called dummy.

I presume from this code that you have filled in a new handler in the hypercall_table, but have you set the expected number of args in the hypercall_args_table?

The default number of args is 0, which cases a debug Xen to deliberately clobber all the registers to 0xdeadbeef

~Andrew

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