Re: [PATCH 1/2] trace: improve usefulness of hypercall trace record

[David Vrabel <david.vrabel@citrix.com>]

On 28/05/12 17:03, Frediano Ziglio wrote:
> On Thu, 2012-05-24 at 11:37 +0100, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@citrix.com>
>>
>> Trace hypercalls using a more useful trace record format.
>>
>> The EIP field is removed (it was always somewhere in the hypercall
>> page) and include selected hypercall arguments (the number of calls in
>> a multicall, and the number of PTE updates in an mmu_update).
>>
> 
> I think that EIP is quite useful as it allow to understand which code in
> dom0 call that hypercall.

The EIP was always an address in the hypercall page (i.e.,
hypercall_page + op * sizeof(unsigned long)) and doesn't tell you what
made the hypercall.  You would need one of the addresses off the guest
stack to find the caller.

> There is also space for an additional parameter without changing trace
> version (adding information in a record should not be a problem).

True, but George was keen on keeping the trace record size to a minimum.

I am tempted to use 5 bits of the first extra word to indicate which
parameters are present in the trace record.  This might make the new
format more future-proof, perhaps.

David