Re: [Xen-devel] [PATCH v5 for-4.9 1/4] hvm/dmop: Box dmop_bufs rather than passing two parameters around

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 10/04/17 10:04, Paul Durrant wrote:
>> -----Original Message-----
>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>> Sent: 07 April 2017 20:36
>> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
>> Cc: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>; Andrew Cooper
>> <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich <JBeulich@xxxxxxxx>; Paul
>> Durrant <Paul.Durrant@xxxxxxxxxx>; Julien Grall <julien.grall@xxxxxxx>
>> Subject: [PATCH v5 for-4.9 1/4] hvm/dmop: Box dmop_bufs rather than
>> passing two parameters around
>>
>> From: Jennifer Herbert <Jennifer.Herbert@xxxxxxxxxx>
>>
>> No functional change.
>>
> Why is this a good thing? Passing two parameters around allowed for them to 
> be in registers. I preferred the code as it was before.

a) It will always be inlined, so registers aren't relevant.  Even if
they were, all values are available directly with the pointer as a base,
so there is no reduction in expressiveness.  (i.e. the previous code
only increases register pressure).
b) passing multiple parameters like that is a recipe for mistakes, and
in this case, mistakes mean security vulnerabilities.
c) It is necessary to make legible code for the later changes in this
series.

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel