#8402: throwTo segfaults under -prof -threaded -with-rtsopts=N2 ----------------------------------+---------------------------------- Reporter: akio | Owner: Type: bug | Status: patch Priority: highest | Milestone: 7.8.1 Component: Profiling | Version: 7.7 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 (amd64) Type of failure: Runtime crash | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: ----------------------------------+---------------------------------- Comment (by ezyang): OK, I understand what is going on here. It useful to think of the various cases that the RTS can be compiled. When the RTS is compiled as profiling and debugging, some of the sanity check code expects closures to be zeroed (specifically checkFullHeap, which explicitly looks for slop like things): {{{ /* skip over slop */ while (p < bd->free && (*p < 0x1000 || !LOOKS_LIKE_INFO_PTR(*p))) { p++; } }}} So we must zero out the slop in that case. However, when RTS is compiled as profiling and multithreaded, as Simon points out (and I didn't realize when making my patch), it's not OK to zero slop when threaded. So Akio's patch prevents the slop from zeroed in this case. Serendipitously, we already had disabled full heap checks when compiling with the threaded RTS. So I think the proper conditional here is: {{{ // It is never valid to overwrite slop when multithreaded #if defined(THREADED_RTS) return; // We need to overwrite slop when: // - We are LDV profiling // - We have a debug RTS which will do full heap checks #elif defined(PROFILING) && !DEBUG if (era <= 0) return; #endif }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8402#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler