[PATCH] Allow importing data symbols from a DLL for MSVC clients

[Peter Rosin <peda at lysator dot liu dot se>]

---
 ChangeLog        |    7 +++++++
 Makefile.am      |    2 +-
 Makefile.in      |    2 +-
 include/ffi.h.in |   40 +++++++++++++++++++++++++++-------------
 4 files changed, 36 insertions(+), 15 deletions(-)

Hi!

This is a "real" version of the patch at the end of my MSVC ramblings(1).

With this on top of the other 6 patches, I can configure with:

.../configure \
  CC="/c/Cygwin/home/<usename>/libffi/compile cl -nologo" \
  CFLAGS="-MD -Zi" \
  CXX="/c/Cygwin/home/<username>/libffi/compile cl -nologo" \
  CXXFLAGS="-MD -Zi" \
  NM="dumpbin -symbols" \
  --enable-dependency-tracking 

Cheers,
Peter

(1) http://sourceware.org/ml/libffi-discuss/2012/msg00144.html

diff --git a/ChangeLog b/ChangeLog
index 32577f1..f4aaa06 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2012-03-23  Peter Rosin  <peda@lysator.liu.se>
+
+	* Makefile.am (AM_CPPFLAGS): Add -DFFI_BUILDING.
+	* Makefile.in: Rebuilt.
+	* include/ffi.h.in [MSVC]: Add __declspec(dllimport) decorations
+	to all data exports, when compiling libffi clients using MSVC.
+
 2012-03-21  Peter Rosin	 <peda@lysator.liu.se>
 
 	* testsuite/libffi.call/float_va.c (float_va_fn): Use %f when
diff --git a/Makefile.am b/Makefile.am
index 2c2444e..fcb2098 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -194,7 +194,7 @@ endif
 
 libffi_la_LDFLAGS = -version-info `grep -v '^\#' $(srcdir)/libtool-version` $(LTLDFLAGS) $(AM_LTLDFLAGS)
 
-AM_CPPFLAGS = -I. -I$(top_srcdir)/include -Iinclude -I$(top_srcdir)/src
+AM_CPPFLAGS = -I. -I$(top_srcdir)/include -Iinclude -I$(top_srcdir)/src -DFFI_BUILDING
 AM_CCASFLAGS = $(AM_CPPFLAGS) -g
 
 # No install-html or install-pdf support in automake yet
diff --git a/Makefile.in b/Makefile.in
index 6bf6cc5..4a79a3d 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -510,7 +510,7 @@ libffi_convenience_la_SOURCES = $(libffi_la_SOURCES)
 nodist_libffi_convenience_la_SOURCES = $(nodist_libffi_la_SOURCES)
 AM_CFLAGS = -g $(am__append_29)
 libffi_la_LDFLAGS = -version-info `grep -v '^\#' $(srcdir)/libtool-version` $(LTLDFLAGS) $(AM_LTLDFLAGS)
-AM_CPPFLAGS = -I. -I$(top_srcdir)/include -Iinclude -I$(top_srcdir)/src
+AM_CPPFLAGS = -I. -I$(top_srcdir)/include -Iinclude -I$(top_srcdir)/src -DFFI_BUILDING
 AM_CCASFLAGS = $(AM_CPPFLAGS) -g
 all: fficonfig.h
 	$(MAKE) $(AM_MAKEFLAGS) all-recursive
diff --git a/include/ffi.h.in b/include/ffi.h.in
index 84017f1..4f3b3de 100644
--- a/include/ffi.h.in
+++ b/include/ffi.h.in
@@ -166,22 +166,36 @@ typedef struct _ffi_type
  #error "long size not supported"
 #endif
 
+/* Need minimal decorations for DLLs to works on Windows. */
+/* GCC has autoimport and autoexport.  Rely on Libtool to */
+/* help MSVC export from a DLL, but always declare data   */
+/* to be imported for MSVC clients.  This costs an extra  */
+/* indirection for MSVC clients using the static version  */
+/* of the library, but don't worry about that.  Besides,  */
+/* as a workaround, they can define FFI_BUILDING if they  */
+/* *know* they are going to link with the static library. */
+#if defined _MSC_VER && !defined FFI_BUILDING
+#define FFI_EXTERN extern __declspec(dllimport)
+#else
+#define FFI_EXTERN extern
+#endif
+
 /* These are defined in types.c */
-extern ffi_type ffi_type_void;
-extern ffi_type ffi_type_uint8;
-extern ffi_type ffi_type_sint8;
-extern ffi_type ffi_type_uint16;
-extern ffi_type ffi_type_sint16;
-extern ffi_type ffi_type_uint32;
-extern ffi_type ffi_type_sint32;
-extern ffi_type ffi_type_uint64;
-extern ffi_type ffi_type_sint64;
-extern ffi_type ffi_type_float;
-extern ffi_type ffi_type_double;
-extern ffi_type ffi_type_pointer;
+FFI_EXTERN ffi_type ffi_type_void;
+FFI_EXTERN ffi_type ffi_type_uint8;
+FFI_EXTERN ffi_type ffi_type_sint8;
+FFI_EXTERN ffi_type ffi_type_uint16;
+FFI_EXTERN ffi_type ffi_type_sint16;
+FFI_EXTERN ffi_type ffi_type_uint32;
+FFI_EXTERN ffi_type ffi_type_sint32;
+FFI_EXTERN ffi_type ffi_type_uint64;
+FFI_EXTERN ffi_type ffi_type_sint64;
+FFI_EXTERN ffi_type ffi_type_float;
+FFI_EXTERN ffi_type ffi_type_double;
+FFI_EXTERN ffi_type ffi_type_pointer;
 
 #if @HAVE_LONG_DOUBLE@
-extern ffi_type ffi_type_longdouble;
+FFI_EXTERN ffi_type ffi_type_longdouble;
 #else
 #define ffi_type_longdouble ffi_type_double
 #endif
-- 
1.7.9