On 01/31/2018 01:28 AM, Eric Botcazou wrote: >> -fstack-check and -fstack-clash both potentially create a loop for stack >> probing. In that case they both need a scratch register to hold the >> loop upper bound. >> >> The code to allocate a scratch register first starts with the >> caller-saved registers as they're zero cost. Then it'll use any callee >> saved register that is actually saved. If neither is available (say >> because all the caller-saved regs are used for parameter passing and >> there are no callee saved register used), then the allocation routine >> will push %eax on the stack and the deallocation routine will pop it off >> to restore its value. >> >> Of course there is a *stack allocation* between those two points. So >> the pop ends up restoring garbage into the register. > > There is a stack allocation only on Linux, there isn't any on Solaris, *BSD, > Windows, LynxOS and other OSes where you can probe below the stack pointer. Ack. Let's hold the patch until I can test *that* path.
jeff
