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I've encountered a panic when building a cross ghc for aarch64. Steps to reproduce:

Clone ghc repo and then (on an x86_64 machine):

$ git checkout tags/ghc-8.8.4-release
$ git submodule update --init
$ echo "HADDOCK_DOCS=NO" > mk/build.mk
$ ./configure --target=aarch64-linux-gnu --prefix=/home/matthew/Development/ghc/arm/ --with-curses-libraries=/home/matthew/arm/lib/
$ make

The /home/matthew/arm/lib/ dir contains a cross compiled version of ncurses.

Then I get the error:

"inplace/bin/ghc-stage1" -hisuf hi -osuf  o -hcsuf hc -static  -H32m -O -Wall     -this-unit-id filepath-1.4.2.1 -hide-all-packages -i -ilibraries/filepath/. -ilibraries/filepath/dist-install/build -Ilibraries/filepath/dist-install/build -ilibraries/filepath/dist-install/build/./autogen -Ilibraries/filepath/dist-install/build/./autogen -Ilibraries/filepath/.    -optP-include -optPlibraries/filepath/dist-install/build/./autogen/cabal_macros.h -package-id base-4.13.0.0 -Wall -XHaskell2010 -O2 -haddock  -no-user-package-db -rtsopts  -Wno-deprecated-flags    -Wnoncanonical-monad-instances  -outputdir libraries/filepath/dist-install/build  -split-sections -dynamic-too -c libraries/filepath/./System/FilePath/Posix.hs -o libraries/filepath/dist-install/build/System/FilePath/Posix.o -dyno libraries/filepath/dist-install/build/System/FilePath/Posix.dyn_o
ghc-stage1: panic! (the 'impossible' happened)
  (GHC version 8.8.4 for aarch64-unknown-linux):
        Prelude.chr: bad argument: 808988985

Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

Enviroment:

• bootstrapping ghc version: The Glorious Glasgow Haskell Compilation System, version 8.8.4
• aarch64 toolchain: aarch64-linux-gnu-gcc (GCC) 10.2.0
• ncurses version: 6.2