[GHC] #10462: GHCi doesn't work Any and missing RealWorld foreign prim imports

29 May 2015

      #10462: GHCi doesn't work Any and missing RealWorld foreign prim imports
-------------------------------------+-------------------------------------
              Reporter:  ezyang      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  GHCi        |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 Here are two issues with our GHCi support for foreign prim imports:

 Here is a program that works:

 {{{
 {-# LANGUAGE GHCForeignImportPrim, MagicHash, UnliftedFFITypes,
 UnboxedTuples #-}
 module Serum where
 import GHC.Exts

 foreign import prim "cheneycopy" cheneycopy :: Word# -> State# RealWorld
 -> (# State# RealWorld, Word# #)
 }}}

 If I remove the world token passing, as in here:

 {{{
 {-# LANGUAGE GHCForeignImportPrim, MagicHash, UnliftedFFITypes,
 UnboxedTuples #-}
 module Serum where
 import GHC.Exts

 foreign import prim "cheneycopy" cheneycopy :: Word# -> Word#
 }}}

 I get:

 {{{
   (GHC version 7.10.1 for x86_64-unknown-linux):
         ByteCodeGen.generateCCall: missing or invalid World token?
 }}}

 Another error is if I try to pass Any as an argument:

 {{{
 {-# LANGUAGE GHCForeignImportPrim, MagicHash, UnliftedFFITypes,
 UnboxedTuples #-}
 module Serum where
 import GHC.Exts

 foreign import prim "cheneycopy" cheneycopy :: Any -> State# RealWorld ->
 (# State# RealWorld, Word# #)
 }}}

 Then I get:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.10.1 for x86_64-unknown-linux):
         primRepToFFIType
 }}}

 Note to anyone who is running into this problem: an easy workaround is to
 use `-fobject-code` which bypasses bytecode generation.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10462
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