[commit: ghc] master: LlvmMangler: Be more selective when mangling object types (5895f2b)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/5895f2b8ffba72a8393e9f712461e6e5ed7ceced/ghc

>---------------------------------------------------------------

commit 5895f2b8ffba72a8393e9f712461e6e5ed7ceced
Author: Ben Gamari <bgamari.foss at gmail.com>
Date:   Fri Aug 15 11:11:17 2014 -0400

    LlvmMangler: Be more selective when mangling object types
    
    Summary:
    We previously did a wholesale replace of `%function` to `%object` to
    mangle object `.type` annotations. This is bad as it can end up
    replacing appearances of `"%function"` in the user's code. We now look
    for a proper `.type` keyword before performing the replacement.
    
    Thanks to @rwbarton for pointing out the bug.
    
    Test Plan:
    Previously,
    
        $ echo 'main = putStrLn "@function"' > test.hs
        $ ghc -fllvm test.hs
        $ ./test
        @object
    
    Now,
        $ echo 'main = putStrLn "@function"' > test.hs
        $ ghc -fllvm test.hs
        $ ./test
        @function
    
    Reviewers: rwbarton, austin
    
    Reviewed By: rwbarton, austin
    
    Subscribers: phaskell, simonmar, relrod, ezyang, carter
    
    Differential Revision: https://phabricator.haskell.org/D150
    
    GHC Trac Issues: #9439


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5895f2b8ffba72a8393e9f712461e6e5ed7ceced
 compiler/llvmGen/LlvmMangler.hs | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/compiler/llvmGen/LlvmMangler.hs b/compiler/llvmGen/LlvmMangler.hs
index 7084a2e..8652a89 100644
--- a/compiler/llvmGen/LlvmMangler.hs
+++ b/compiler/llvmGen/LlvmMangler.hs
@@ -58,13 +58,23 @@ llvmFixupAsm dflags f1 f2 = {-# SCC "llvm_mangler" #-} do
     hClose w
     return ()
 
+-- | This rewrites @.type@ annotations of function symbols to @%object at .
+-- This is done as the linker can relocate @%functions@ through the
+-- Procedure Linking Table (PLT). This is bad since we expect that the
+-- info table will appear directly before the symbol's location. In the
+-- case that the PLT is used, this will be not an info table but instead
+-- some random PLT garbage.
 rewriteSymType :: B.ByteString -> B.ByteString
 rewriteSymType s =
-    foldl (\s' (typeFunc,typeObj)->replace typeFunc typeObj s') s types
+    B.unlines $ map (rewrite '@' . rewrite '%') $ B.lines s
   where
-    types = [ (B.pack "@function", B.pack "@object")
-            , (B.pack "%function", B.pack "%object")
-            ]
+    rewrite :: Char -> B.ByteString -> B.ByteString
+    rewrite prefix x
+        | isType x = replace funcType objType x
+        | otherwise = x
+      where
+        funcType = prefix `B.cons` B.pack "function"
+        objType  = prefix `B.cons` B.pack "object"
 
 -- | Splits the file contents into its sections
 readSections :: Handle -> Handle -> IO [Section]