On Wed, May 1, 2013 at 4:33 AM, Peter Maydell <peter.mayd...@linaro.org>wrote:
> On 1 May 2013 11:19, Laurent Desnogues <laurent.desnog...@gmail.com> > wrote: > > On Wednesday, May 1, 2013, Richard Henderson <r...@twiddle.net> wrote: > >> On 2013-04-30 07:36, John Rigby wrote: > >>> > >>> uint32_t regs[16]; > >>> + > >>> + /* Regs for A64 mode. */ > >>> + uint64_t xregs[31]; > >>> + uint64_t pc; > >>> + uint64_t sp; > >>> + uint32_t pstate; > >>> + uint32_t aarch64_state; /* 1 if CPU is in aarch64 state */ > >>> + > >> > >> How do these registers overlap (or not) in real hardware? > >> Is it possible to union these with the 32-bit state? > > > > There is an overlap between 32- and 64-bit state registers, > > but it's against the set of 32 (?) 32-bit registers that exist > > across all modes, not against the 16 registers as used here. > > > > IMHO it doesn't make sense to union them, the mapping > > can be done when switching from 32- to 64-bit modes. > > Agreed -- the 32/64 switch only ever happens when taking > or returning from an exception, so it is easier to get > the overlap semantics right with explicit code there > rather than try to change all the existing 32 bit code > to implicitly get things right. Plus as you say the > interaction with aarch32 register banking would make > unioning tricky. > > I think the other thing we need here is a comment stating exactly what peter has said explaining why the two sets of registers exist and that the aarch64 field indicates which set is active. --john
