Re: Passing pointers to hypercalls

[Andrew Cooper <andrew.cooper3@citrix.com>]

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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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