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. -- PMM
