File ghc.git-e18525f.patch of Package ghc

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File ghc.git-e18525f.patch of Package ghc (Revision 7a25787aeb108f49c93bd94cf473630a)

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From: Sergei Trofimovich <slyfox@gentoo.org>
Date: Thu, 4 Sep 2014 14:50:45 +0000 (+0300)
Subject: pprC: declare extern cmm primitives as functions, not data
X-Git-Url: https://git.haskell.org/ghc.git/commitdiff_plain/e18525fae273f4c1ad8d6cbe1dea4fc074cac721

pprC: declare extern cmm primitives as functions, not data

Summary:
  The commit fixes incorrect code generation of
  integer-gmp package on ia64 due to C prototypes mismatch.
  Before the patch prototypes for "foreign import prim" were:
      StgWord poizh[];
  After the patch they became:
      StgFunPtr poizh();

Long story:

Consider the following simple example:

{-# LANGUAGE MagicHash, GHCForeignImportPrim, UnliftedFFITypes #-}
    module M where
    import GHC.Prim -- Int#
    foreign import prim "poizh" poi# :: Int# -> Int#

Before the patch unregisterised build generated the
following 'poizh' reference:
    EI_(poizh); /* StgWord poizh[]; */
    FN_(M_poizh_entry) {
    // ...
    JMP_((W_)&poizh);
    }

After the patch it looks this way:
    EF_(poizh); /* StgFunPtr poizh(); */
    FN_(M_poizh_entry) {
    // ...
    JMP_((W_)&poizh);
    }

On ia64 it leads to different relocation types being generated:
  incorrect one:
    addl r14 = @ltoffx(poizh#)
    ld8.mov r14 = [r14], poizh# ; r14 = address-of 'poizh#'
  correct one:
    addl r14 = @ltoff(@fptr(poizh#)), gp ; r14 = address-of-thunk 'poizh#'
    ld8 r14 = [r14]

'@fptr(poizh#)' basically instructs assembler to creates
another obect consisting of real address to 'poizh' instructions
and module address. That '@fptr' object is used as a function "address"
This object is different for every module referencing 'poizh' symbol.

All indirect function calls expect '@fptr' object. That way
call site reads real destination address and set destination
module address in 'gp' register from '@fptr'.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---

Index: ghc-7.8.3/compiler/cmm/CLabel.hs
===================================================================
--- ghc-7.8.3.orig/compiler/cmm/CLabel.hs
+++ ghc-7.8.3/compiler/cmm/CLabel.hs
@@ -801,6 +801,7 @@ labelType (CmmLabel _ _ CmmClosure)
 labelType (CmmLabel _ _ CmmCode)                = CodeLabel
 labelType (CmmLabel _ _ CmmInfo)                = DataLabel
 labelType (CmmLabel _ _ CmmEntry)               = CodeLabel
+labelType (CmmLabel _ _ CmmPrimCall)            = CodeLabel
 labelType (CmmLabel _ _ CmmRetInfo)             = DataLabel
 labelType (CmmLabel _ _ CmmRet)                 = CodeLabel
 labelType (RtsLabel (RtsSelectorInfoTable _ _)) = DataLabel

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