Re: [Qemu-devel] Re: Compile files only once: some planning

[Blue Swirl]

On 3/24/10, Richard Henderson <address@hidden> wrote:
> On 03/24/2010 02:47 AM, Paolo Bonzini wrote:
>
> > 1) make CPUState define only common fields. Include CPUState at the
> > beginning of each per-target CPUXYZState.
> >
>
>  Irritatingly, the common fields contain quite big TLBs.  And the
>  offsets from the start of env affect the compactness of the code
>  generated from TCG.  We really really want the general registers
>  to come first to make sure that those offsets fit the host's
>  reg+offset addressing mode.

One trick is to define a fixed offset (about half CPUState size) and
make env point to CPUState + offset. Then the negative part of the
offset space can be used efficiently. But this just doubles the space
that can be accessed fast, so it's not a big win.