Here I am, minding my own business, building GHC 6.10.4 with GHC 6.6 and I see this in the build output: --8<---------------cut here---------------start------------->8--- /gnu/store/km47738v7q4qgym9zkggngqxr05q165h-ghc-6.6/bin/ghc -#include cutils.h -DSTAGE=1 -package-name ghc-6.10.4 -hide-all-packages -no-user-package-conf -package-conf /tmp/guix-build-ghc-6.10.4.drv-0/ghc-6.10.4/libraries/bootstrapping.conf -i -idist-stage1/build -inativeGen -ibasicTypes -icmm -icodeGen -icoreSyn -icprAnalysis -ideSugar -ighci -ihsSyn -iiface -imain -iparser -iprelude -iprofiling -irename -isimplCore -isimplStg -ispecialise -istgSyn -istranal -itypecheck -itypes -iutils -ivectorise -idist-stage1/build/autogen -Idist-stage1/build/autogen -Idist-stage1/build -Istage1 -I../libraries/base/cbits -I../libraries/base/include -I. -Iparser -Iutils -optP-include -optPdist-stage1/build/autogen/cabal_macros.h -odir dist-stage1/build -hidir dist-stage1/build -package Cabal-1.6.0.3 -package base-2.0 -package extensible-exceptions-0.1.1.0 -package filepath-1.1.0.2 -package haskell98-1.0 -package hpc-0.5.0.3 -package unix-1.0 -O -Wall -fno-warn-name-shadowing -fno-warn-orphans -fglasgow-exts -cpp -fffi -fscoped-type-variables -idist-stage1/build -H32m -O -Rghc-timing -c nativeGen/MachCodeGen.hs -o dist-stage1/build/MachCodeGen.o -ohi dist-stage1/build/MachCodeGen.hi /tmp/guix-build-ghc-6.10.4.drv-0/ghc7957_0/ghc7957_0.hc: In function ���@ build-log 17895 2 ��@ build-log 17895 2 sb@ build-log 17895 3 ZI_@ build-log 17895 2 0_@ build-log 17895 2 al@ build-log 17895 2 t�@ build-log 17895 2 ��@ build-log 17895 2 : /tmp/guix-build-ghc-6.10.4.drv-0/ghc7957_0/ghc7957_0.hc:2881:1: warning: implicit declaration of function ‘stg_intToInt64’ [-Wimplicit-function-declaration] _s9Fa = (StgWord64)stg_intToInt64((I_)_cc02); ^ /tmp/guix-build-ghc-6.10.4.drv-0/ghc7957_0/ghc7957_0.hc:2884:1: warning: implicit declaration of function ‘stg_negateInt64’ [-Wimplicit-function-declaration] _s9Ff = (StgWord64)stg_negateInt64((StgInt64)_s9Fa); ^ /tmp/guix-build-ghc-6.10.4.drv-0/ghc7957_0/ghc7957_0.hc: In function ‘sbZI_1_alt’: /tmp/guix-build-ghc-6.10.4.drv-0/ghc7957_0/ghc7957_0.hc:2910:1: warning: implicit declaration of function ���@ build-log 17895 1 �@ build-log 17895 1 �@ build-log 17895 1 s@ build-log 17895 1 t@ build-log 17895 1 g@ build-log 17895 1 _@ build-log 17895 1 i@ build-log 17895 1 n@ build-log 17895 1 t@ build-log 17895 1 e@ build-log 17895 1 g@ build-log 17895 1 e@ build-log 17895 1 r@ build-log 17895 1 T@ build-log 17895 1 o@ build-log 17895 1 I@ build-log 17895 1 n@ build-log 17895 1 t@ build-log 17895 1 6@ build-log 17895 1 4@ build-log 17895 1 �@ build-log 17895 1 �@ build-log 17895 1 �@ build-log 17895 1 @ build-log 17895 1 [@ build-log 17895 1 -@ build-log 17895 1 W@ build-log 17895 1 i@ build-log 17895 1 m@ build-log 17895 1 p@ build-log 17895 1 l@ build-log 17895 1 i@ build-log 17895 1 c@ build-log 17895 1 i@ build-log 17895 1 t@ build-log 17895 1 -@ build-log 17895 1 f@ build-log 17895 1 u@ build-log 17895 1 n@ build-log 17895 1 c@ build-log 17895 1 t@ build-log 17895 1 i@ build-log 17895 1 o@ build-log 17895 1 n@ build-log 17895 1 -@ build-log 17895 1 d@ build-log 17895 1 e@ build-log 17895 1 c@ build-log 17895 1 l@ build-log 17895 1 a@ build-log 17895 1 r@ build-log 17895 1 a@ build-log 17895 1 t@ build-log 17895 1 i@ build-log 17895 1 o@ build-log 17895 1 n@ build-log 17895 1 ]@ build-log 17895 1 _s9Fq = (StgWord64)stg_integerToInt64((I_)_cc0a, (void *)_cc09); ^ --8<---------------cut here---------------end--------------->8--- Whatever this “���” is, it seems to have escaped the build log filter. -- Ricardo