Fix building of the RTS with the NCG under Windows

[ghc-hetmet.git] / compiler / nativeGen / PIC.hs

diff --git a/compiler/nativeGen/PIC.hs b/compiler/nativeGen/PIC.hs
index 98e4f9f..eb233e0 100644 (file)
--- a/compiler/nativeGen/PIC.hs
+++ b/compiler/nativeGen/PIC.hs
@@ -192,16 +192,40 @@ data LabelAccessStyle
 howToAccessLabel 
        :: DynFlags -> Arch -> OS -> ReferenceKind -> CLabel -> LabelAccessStyle
 
+
 -- Windows
--- 
--- We need to use access *exactly* those things that
--- are imported from a DLL via an __imp_* label.
--- There are no stubs for imported code.
+-- In Windows speak, a "module" is a set of objects linked into the
+-- same Portable Exectuable (PE) file. (both .exe and .dll files are PEs).
+--
+-- If we're compiling a multi-module program then symbols from other modules
+-- are accessed by a symbol pointer named __imp_SYMBOL. At runtime we have the
+-- following.
+--
+--   (in the local module)
+--     __imp_SYMBOL: addr of SYMBOL
+--
+--   (in the other module)
+--     SYMBOL: the real function / data.
+--
+-- To access the function at SYMBOL from our local module, we just need to
+-- dereference the local __imp_SYMBOL.
+--
+-- If opt_Static is set then we assume that all our code will be linked
+-- into the same .exe file. In this case we always access symbols directly, 
+-- and never use __imp_SYMBOL.
 --
 howToAccessLabel dflags _ OSMinGW32 _ lbl
+
+       -- Assume all symbols will be in the same PE, so just access them directly.
+       | opt_Static
+       = AccessDirectly
+       
+       -- If the target symbol is in another PE we need to access it via the
+       --      appropriate __imp_SYMBOL pointer.
        | labelDynamic (thisPackage dflags) lbl 
        = AccessViaSymbolPtr
 
+       -- Target symbol is in the same PE as the caller, so just access it directly.
        | otherwise
        = AccessDirectly
 
@@ -300,9 +324,9 @@ howToAccessLabel dflags arch OSLinux DataReference lbl
 
 
        -- In most cases, we have to avoid symbol stubs on ELF, for the following reasons:
-       -- * on i386, the position-independent symbol stubs in the Procedure Linkage Table
+       --   on i386, the position-independent symbol stubs in the Procedure Linkage Table
        --   require the address of the GOT to be loaded into register %ebx on entry.
-       -- * The linker will take any reference to the symbol stub as a hint that
+       --   The linker will take any reference to the symbol stub as a hint that
        --   the label in question is a code label. When linking executables, this
        --   will cause the linker to replace even data references to the label with
        --   references to the symbol stub.
@@ -445,9 +469,8 @@ pprGotDeclaration ArchX86 OSDarwin
                ptext (sLit "\tmovl (%esp), %eax"),
                ptext (sLit "\tret") ]
 
-       | otherwise
-       = empty
-       
+pprGotDeclaration _ OSDarwin
+       = Pretty.empty
                
 -- pprGotDeclaration
 -- Output whatever needs to be output once per .s file.