Hi, while working on an ghc update for OpenBSD (to ghc-8.2.2), I tested a diff for OpenBSD which enforces a special mmap(2) option, MAP_STACK for the system stack and, if the check fails, just aborts the process.[1] (Please note that this differs from the meaning of MAP_STACK on some other operating systems) At first, everything looked fine, but later during the build, *sometimes* ghc (to be specific, inplace/lib/bin/ghc-stage2) got aborted after *many* succesfull runs of it (for example, while compiling the bundled haddock and after already a couple of haddock sources had been successfully compiled). So, if the stack pointer checking diff to OpenBSD is correct, and if I'm not running into a completely unrelated problem: does ghc and/or the runtime library sometimes move the system stack pointer to newly allocated/mapped memory? If so, where in the code? Please note: the check happens on traps and system calls, so the doesn't happen when the stack pointer is changed to newly allocated/mapped memory, but after the next trap or system call. Unfurtunately, I was stupid enough to drop my recent build logs and back traces, but they weren't very enlightening, anyway ;-) I may to get some more information tomorrow or on thursday. I'd appreciate any help on this. After all it's probably just a matter of changing one call to mmap(2), shielded by an #ifdef. Ciao and thanks in advance for any help, Kili [1]: https://marc.info/?l=openbsd-tech&m=151572838911297&w=2