On 26 December 2013 21:27, Peter Maydell <peter.mayd...@linaro.org> wrote:
> Why is it OK to skip the addition of the base address for ES
> (in the movl_A0_EDI case) when the comment for addseg says
> it only applies to CS/DS/ES?
Scratch that, misread of the comment. addseg applies to DS/ES/SS.
> Why is it not OK to skip the addition
> of the base address for CS/DS/ES if it was specified by an
> override prefix rather than being the default for the insn?
This still applies though.
> It seems to me that we ought to try to get this code to a
> point where it looks more like:
> if (ovr_seg < 0) {
> ovr_seg = def_seg;
> }
> emit code to get address;
> if (!segment_base_guaranteed_zero(s, ovr_seg)) {
> emit code to add base to address;
> }
>
> where segment_base_guaranteed_zero() is a helper
> function like:
> bool segment_base_guaranteed_zero(s, seg) {
> /* Return true if we can guarantee at translate time that
> * the base address of the specified segment is zero
> * (and thus can skip emitting code to add it)
> */
> return (!s->addseg &&
> (seg == R_CS || seg == R_DS || seg == R_SS));
s/R_CS/R_ES/;
> }
thanks
-- PMM
