fails to unpack a ghc bindist properly

[hasufell]

Unpacking a ghc bindist with tar is broken.

1. extract/unpack does not preserve executable files #25 will cause make to fail, because various files are missing executable bit
2. It screws up some files (including their filepaths). Running configure and make (after fixing exec bits) results in

ghc-cabal: Error: Could not find module:
Data.ByteString.Builder.Prim.Internal.UncheckedShifts with any suffix: ["hi"]
in the search path: ["dist-install/build"]
ghc.mk:985: recipe for target 'install_packages' failed
make[1]: *** [install_packages] Error 1
Makefile:51: recipe for target 'install' failed
make: *** [install] Error 2

And indeed, searching for UncheckedShifts results in odd output (yes, the filename is truncated):

$ find . -type f -iname '*unchecked*'
./libraries/bytestring/dist-install/build/Data/ByteString/Builder/Prim/Internal/UncheckedShi

Searching a healthy unpacked dir (unpacked with cli tar) results in:

$ find . -type f -iname '*unchecked*'
./libraries/bytestring/dist-install/doc/html/bytestring/src/Data-ByteString-Builder-Prim-Internal-UncheckedShifts.html
./libraries/bytestring/dist-install/build/Data/ByteString/Builder/Prim/Internal/UncheckedShifts.hi
./libraries/bytestring/dist-install/build/Data/ByteString/Builder/Prim/Internal/UncheckedShifts.dyn_hi
./libraries/bytestring/dist-install/build/Data/ByteString/Builder/Prim/Internal/UncheckedShifts.p_hi

I couldn't reproduce it with a single overly long path. So I'm not sure this is a problem with path length. I suspect there is some really dangerous memory bug here.

Edit: I could reproduce it with a single file: https://github.com/hasufell/tar-bug/releases/download/0.1.1/ghc-8.6.5.tar

[hasufell]

It seems ././@LongLink is not handled correctly: https://stackoverflow.com/questions/2078778/what-exactly-is-the-gnu-tar-longlink-trick