Re: [Qemu-devel] [PULL 0/3] 128-bit support for the memory API

[Anthony Liguori <anthony@codemonkey.ws>]

On 10/30/2011 09:02 AM, Avi Kivity wrote:
> This somewhat controversial patchset converts internal arithmetic in the
> memory API to 128 bits.
>
> It has been argued that with careful coding we can make 64-bit work as
> well.  I don't think this is true in general - a memory router can adjust
> addresses either forwards or backwards, and some buses (PCIe) need the
> full 64-bit space - though it's probably the case for all the configurations
> we support today.  Regardless, the need for careful coding means subtle bugs,
> which I don't want in a core API that is driven by guest supplied values.

The primary need for signed arithmetic is aliases, correct?

Where do we actually make use of this in practice?   I think having negative 
address spaces is a weird aspect of the memory api and wonder if refactoring it 
away is a better solution tot he problem.

Regards,

Anthony Liguori

>
> Avi Kivity (3):
>    Add support for 128-bit arithmetic
>    memory: use 128-bit integers for sizes and intermediates
>    Adjust system and pci address spaces to full 64-bit
>
>   exec.c          |    2 +-
>   hw/pc_piix.c    |    2 +-
>   hw/pci_bridge.c |    2 +-
>   int128.h        |  116 ++++++++++++++++++++++++++++++++
>   memory.c        |  196 ++++++++++++++++++++++++++++++++----------------------
>   memory.h        |    3 +-
>   6 files changed, 237 insertions(+), 84 deletions(-)
>   create mode 100644 int128.h
>