On Fri, Sep 11, 2020 at 11:52:29AM -0500, Qing Zhao wrote: > I don’t understand why it’s not correct if we clearing call-clobbered > registers > AFTER restoring call-preserved registers?
Because the compiler backend (or the linker! Or the dynamic linker! Etc.) can use volatile registers for their own purposes. Like, on Power, r11 and r12 are used for various calling convention purposes; they are also used for other purposes; and r0 is used as some all-purpose volatile (it typically holds the return address near the end of a function). "Call-clobbered" is pretty meaningless. It only holds meaning for a function calling another, and then only to know which registers lose their value then. It has no semantics for other cases, like a function that will return soonish, as here. Segher
