Re: [Qemu-devel] [PATCH] linux-user: fix wait* syscall status returns

[Peter Maydell]

On 23 November 2011 23:31, Alexander Graf <address@hidden> wrote:
> If it was the same value before, it will still be the same value in guest 
> memory.
>
>  get_guest_s32(status, status_ptr);
>  old_status = status;
>  wait(...)
>  if (old_status != status) {
>    status = convert_status(status);
>    put_guest_s32(status, status_ptr);
>  }

Picking some concrete numbers as an illustration; obviously
they're not really sensible status values:

Suppose guest memory contains the value 1, and that
convert_status(1) == 2. Now if you come out of wait()
and status == 1 (ie old_status == status), then either:
 (a) wait() didn't write to status => do nothing
 (b) wait() did write to status => since convert_status(1) == 2
     we need to write 2 to guest memory

For this approach to work you have to have a conversion
function from guest to host status, I think.

-- PMM