On Fri, 2018-07-20 at 11:11 +0000, Wilco Dijkstra wrote: > Steve Ellcey wrote: > > > Yes, I see where I missed this in aarch64_push_regs > > and aarch64_pop_regs. I think that is why the second of > > Wilco's two examples (f2) is wrong. I am unclear about > > exactly what is meant by writeback and why we have it and > > how that and callee_adjust are used. Any chance someone > > could help me understand this part of the prologue/epilogue > > code better? The comments in aarch64.c/aarch64.h aren't > > really helping me understand what the code is doing or > > why it is doing it.
> Writeback is the same as a base update in a load or store. When > creating the frame there are 3 stack adjustments to be made: > creating stack for locals, pushing callee-saves and reserving space > for outgoing arguments. We merge these stack adjustments as much as > possible and use load/store with writeback for codesize and performance. > See the last part in layout_frame for the different cases. OK, I think I understand this a bit better now. I think my main problem is with the term 'writeback' which I am not used to seeing. But if I understand things correctly we are saving one or two registers and (possibly) updating the stack pointer using auto-increment/auto- decrement in one instruction and that the updating of SP is what you mean by 'writeback'. Correct? Steve Ellcey sell...@cavium.com
