• Tamar Christina's avatar
    Add Windows import library support to the Runtime Linker · 97f2b164
    Tamar Christina authored
    Summary:
    Import libraries are files ending in `.dll.a` and `.lib` depending on which
    compiler creates them (GCC, vs MSVC).
    
    Import Libraries are standard `archive` files that contain object files.
    These object files can have two different formats:
    
    1) The normal COFF Object format for object files
        (contains all ascii data and very little program code, so do not
         try to execute.)
    2) "short import" format which just contains a symbol name and
       the dll in which the symbol can be found.
    
    Import Libraries are useful for two things:
    
    1) Allowing applications that don't support dynamic linking to
       link against the import lib (non-short format) which then
       makes calls into the DLL by loading it at runtime.
    
    2) Allow linking of mutually recursive dlls. if `A.DLL` requires
       `B.DLL` and vice versa, import libs can be used to break the cycle
       as they can be created from the expected exports of the DLLs.
    
    A side effect of having these two capabilities is that Import libs are often
    used to hide specific versions of DLLs behind a non-versioned import lib.
    
    e.g. GCC_S.a (non-conventional import lib) will point to the correct
    `libGCC` DLL. With this support Windows Haskell files can now just link
    to `-lGCC_S` and not have to worry about what the actual name of libGCC is.
    
    Also third party libraries such as `icuuc` use import libs to forward to
    versioned DLLs. e.g. `icuuc.lib` points to `icuuc51.dll` etc.
    
    Test Plan:
    ./validate
    
    Two new tests added T11072gcc T11072msvc
    
    Two binary files have been added to the test folder because the "short"
    import library format doesn't seem to be creatable via `dlltool`
    and requires Microsoft's `lib.exe`.
    
    Reviewers: bgamari, RyanGlScott, erikd, goldfire, austin, hvr
    
    Reviewed By: RyanGlScott, erikd
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D1696
    
    GHC Trac Issues: #11072
    97f2b164
libAS.def 30 Bytes