id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,testcase,blockedby,blocking,related,differential
5441,unsafeCoerce'ing function to GHC.Prim.Any causes segfault,ulfn,simonmar,"The following module is the smallest one I've been able to find exhibiting the bug. Any simplification (that I've tried) results in the problem going away.
{{{
module Any where
import Unsafe.Coerce (unsafeCoerce)
import GHC.Prim (Any)
listmap :: (a -> b) -> [a] -> [b]
listmap f [] = []
listmap f (x : xs) = f x : listmap f xs
data Nat = Z | S Nat
{-# NOINLINE inject #-}
inject :: Nat -> Nat -> Nat
inject m i = i
{-# NOINLINE look #-}
look :: Nat -> String -> Char
look Z _ = '0'
showDigit :: Nat -> () -> Nat -> Char
showDigit base prf d = look (inject base d) """"
toDigits :: Nat -> Nat -> [Nat]
toDigits Z Z = [Z]
coe1 :: (Nat -> String) -> Any
coe1 = unsafeCoerce
coe2 :: Any -> (Nat -> String)
coe2 = unsafeCoerce
showInBase :: Nat -> Any
showInBase base
= coe1 (\n -> listmap
(showDigit base ())
(toDigits base n))
showNat :: Nat -> String
showNat = coe2 (showInBase Z)
}}}
Now given this main module (it needs to be a different module)
{{{
import Any
main = putStrLn (showNat Z)
}}}
Compiling with optimisations:
{{{
$ ghc -O --make Main.hs
...
$ ./Main
Bus error: 10
}}}
Without optimizations it prints 0 as expected.
This has been reproduced on 7.0.3 (Mac OS X) and 7.2.1 (some Linux).
",bug,closed,normal,,Compiler,7.2.1,fixed,,,Unknown/Multiple,x86,Runtime crash,simplCore/should_run/T5441,,,,