Actually, the two problems seem to be the same. A fresh build from scratch yields libraries/random/ghc.mk:5: recipe for target 'libraries/random/dist-install/build/System/Random.o' failed make[1]: *** [libraries/random/dist-install/build/System/Random.o] Segmentation fault Then sniping the command line that tried to build Random.o yields "inplace/bin/ghc-stage2.exe" -hisuf hi -osuf o -hcsuf hc -static -H32m -O -Werror -Wall -H64m -O0 -package-name random-1.0.1.1 -hide-all-packages -i -ilibraries/random/. -ilibraries/random/dist-install/build -ilibraries/random/dist-install/build/autogen -Ilibraries/random/dist-install/build -Ilibraries/random/dist-install/build/autogen -Ilibraries/random/. -optP-include -optPlibraries/random/dist-install/build/autogen/cabal_macros.h -package base-4.7.0.0 -package time-1.4.2 -O2 -XHaskell98 -XCPP -O2 -O -dcore-lint -fno-warn-amp -fno-warn-deprecated-flags -dcore-lint -no-user-package-db -rtsopts -odir libraries/random/dist-install/build -hidir libraries/random/dist-install/build -stubdir libraries/random/dist-install/build -c libraries/random/./System/Random.hs -o libraries/random/dist-install/build/System/Random.o bash: [6536: 1 (255)] tcsetattr: Inappropriate ioctl for device io So this ioctl thing seems to be reported as a seg fault by the make system. Running the same command from a 'cmd' window does give a seg-fault pop-up window. Alas. Running with -dshow-passes shows that it happens during code generation, *** CorePrep: Result size of CorePrep = {terms: 1,214, types: 912, coercions: 52} *** Core Linted result of CorePrep: *** Stg2Stg: *** CodeOutput: *** New CodeGen: *** CPSZ: *** CPSZ: I am totally stuck. Simon From: Simon Peyton Jones Sent: 06 March 2014 22:11 To: ghc-devs@haskell.org Subject: new Windows build problem Sigh. Totally new problem with building GHC (HEAD) on Windows.. "inplace/bin/ghc-stage2.exe" -hisuf hi -osuf o -hcsuf hc -static -H32m -O -Werror -Wall -H64m -O0 -package-name haskell98-2.0.0.3 -hide-all-packages -i -ilibraries/haskell98/. -ilibraries/haskell98/dist-install/build -ilibraries/haskell98/dist-install/build/autogen -Ilibraries/haskell98/dist-install/build -Ilibraries/haskell98/dist-install/build/autogen -Ilibraries/haskell98/. -optP-include -optPlibraries/haskell98/dist-install/build/autogen/cabal_macros.h -package array-0.5.0.0 -package base-4.7.0.0 -package directory-1.2.0.2 -package old-locale-1.0.0.6 -package old-time-1.1.0.2 -package process-1.2.0.0 -package time-1.4.2 -Wall -XHaskell98 -O2 -O -dcore-lint -fno-warn-amp -fno-warn-deprecated-flags -dcore-lint -no-user-package-db -rtsopts -odir libraries/haskell98/dist-install/build -hidir libraries/haskell98/dist-install/build -stubdir libraries/haskell98/dist-install/build -c libraries/haskell98/./Directory.hs -o libraries/haskell98/dist-install/build/Directory.o bash: [6536: 1 (255)] tcsetattr: Inappropriate ioctl for device HEAD $ What on earth is this ioctl stuff? The above is repeatable; same command line, same result. But I'm also getting random seg-faults when building libraries with the stage2 compiler libraries/random/ghc.mk:5: recipe for target 'libraries/random/dist-install/build/System/Random.o' failed make[1]: *** [libraries/random/dist-install/build/System/Random.o] Segmentation fault This is NOT repeatable. Saying 'make' again gets further. Any ideas? Simon