> Sparc has a runtime relocation I've never understood but did manage to break > once, resulting in a long thread to fix: > > http://lists.landley.net/pipermail/aboriginal-landley.net/2011-December/001964.html > > Between that and the weird save half the stack register thing with function > calls on some sort of "wheel"... there's a _reason_ I haven't been able to talk > Rich into adding support for it to musl. > Register windowing, with parts of each window overlapping for function arguments etc... you can kind of think of it as a ring buffer of overlapping register files that's an oversimplification but it was originally intended to accelerate and improve register file usage. MIPS and the rest of the industry abandoned this for improved compile time allocation. I think you might be more likely on MIPS to incur more interrupt latency though since you have to spill to memory (at least on MIPS contemporary to Sparc V8) instead of just switching register windows mileage varies greatly.... From what I remember overflowing the register file is implemented with hardware traps that spill to memory etc... since you don't know that information at compile time. on Sparc so yeah it's quite involved to understand and I certainly don't grasp it fully. So on MIPS you spill the register file to memory, on Sparc you spill register windows to memory... if you have exceeded the supported call depth (which is rather expensive since all the register windows go at once). Note spilling a single variable within a register window is a separate issue. Amazing, a link that actually works and is informative: https://blogs.oracle.com/d/flush-register-windows Chase
