[GHC] #12520: Segfault when using unboxed tuples in GHCi

22 Aug 2016

      #12520: Segfault when using unboxed tuples in GHCi
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           Reporter:  mniip          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  GHCi crash
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 If you put this module in a package:
 {{{#!hs
 {-# LANGUAGE MagicHash, UnboxedTuples #-}

 module Bug ( box, wrap, proxy ) where

 import GHC.Prim

 box :: (# Proxy# a, b #) -> b
 box (# x, y #) = y

 wrap :: b -> Proxy# a -> (# Proxy# a, b #)
 wrap x = \i# -> (# i#, x #)

 proxy :: () -> Proxy# a
 proxy () = proxy#
 }}}

 Then in GHCi you can do:
 {{{
 GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
 Prelude> import Bug
 Prelude Bug> box (wrap "foo" (proxy ()))
 "Segmentation fault (core dumped)
 }}}

 Alternatively you can crash `runhaskell` if you put the above code in
 main.

 It seems that GHCi fails to pickup usage of (# VoidRep, PtrLiftedRep #)
 tuples or something. The same trick works with `State#` in place of
 `Proxy#`, but not with `Int#`.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12520
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