Hi, Maybe the code adding one Int argument to rts_breakpoint_io_action is correct in general since when Pepe Iborra applied the patch to his ghc trunk the test did not crash on his machine. Regardless on my machine the test does not work even with the stock ghc 6.10.2 sources (so even when I do not have the patch applied). Here is how I did the test on my 32 bit archlinux: * downloaded ghc-6.10.2-src.tar.bz2 from http://haskell.org/ghc/download_ghc_6_10_2.html#sources (I did not download the extralibs tarball) * unpacked ghc-6.10.2-src.tar.bz2 and did this in the ghc-6.10.2 directory: ./boot ./configure make * then I did this test: status:0 peter@metod [892] ~/haskell/ghc-6.10.2 % cat a.hs f :: Int -> Int f x = x + 1 a = f 1 status:0 peter@metod [893] ~/haskell/ghc-6.10.2 % ghc/stage2-inplace/ghc --interactive a.hs GHCi, version 6.10.2: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( a.hs, interpreted ) Ok, modules loaded: Main. *Main> :break f Breakpoint 0 activated at a.hs:2:0-10 *Main> :force a zsh: segmentation fault ghc/stage2-inplace/ghc --interactive a.hs status:139 peter@metod [894] ~/haskell/ghc-6.10.2 % The test works ok when I do it with the ghc-custom I have installed (6.10.1 with few of my patches). The same behavior is on my laptop which has only stock uptodate archlinux, and stock ghc 6.10.1 installed (so I think it cannot be because of my few patches in ghc 6.10.1). I did the clean build and the test there too. Well to be precise, it works worse on my laptop since when I try to run ghci 6.10.1 (as distributed by archlinux) I'll get a crash too: status:0 peter@dwarf [852] ~/haskell/ghc-6.10.2 % ghci a.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( a.hs, interpreted ) Ok, modules loaded: Main. *Main> :break f Breakpoint 0 activated at a.hs:2:0-10 *Main> :force a% status:139 peter@dwarf [853] ~/haskell/ghc-6.10.2 % The question is: Is the test supposed to work with ghc 6.10.2 without installing it? I hope I'm doing some stupid mistake and that archlinux is not borked. What is the platform (distribution and it's version) ghc HQ uses for ghc development (on which the test I presented works)? Thanks, Peter.