On Tue Mar 28, 2023 at 3:46 AM AEST, Christophe Leroy wrote: > > > Le 25/03/2023 à 14:06, Nicholas Piggin a écrit : > > The _switch stack frame setup are substantially the same, so are the > > comments. The difference in how the stack and current are switched, > > and other hardware and software housekeeping is done is moved into > > macros. > > > > Signed-off-by: Nicholas Piggin <npig...@gmail.com> > > --- > > These patches are mostly just shuffling code around. Better? Worse? > > I find it nice, at least for PPC32 part. > > For PPC32 generated code is almost the same, only a few reordering at > the start of the function. > > Before the change I have: > > 00000238 <_switch>: > 238: 94 21 ff 30 stwu r1,-208(r1) > 23c: 7c 08 02 a6 mflr r0 > 240: 90 01 00 d4 stw r0,212(r1) > 244: 91 a1 00 44 stw r13,68(r1)
Hmm, this is how GCC seems to emits stack prologue code for ppc32. On ppc64 the mflr r0 comes first, then the non-volatile register saving, then the LR save, then ther r1 stdu. Seems a bit pointless to have to different implementations. I think we'd like to have LR saved before r1 though, otherwise you get an unreliable backtrace in your last 2 stack frames instead of just the last one, don't you? Thanks, Nick
