Expand support for symbol versioning to also allow multiple functions

with the same name to exist with bindings to different versions.

CMakeLists.txt

@@ -1109,6 +1109,9 @@ if(NOT DEFINED BUILD_SHARED_LIBS OR BUILD_SHARED_LIBS)
             set_target_properties(zlib PROPERTIES COMPILE_FLAGS "-fno-semantic-interposition")
         endif()
         if(NOT APPLE)
+            if(NOT ZLIB_COMPAT)
+                add_definitions(-DHAVE_SYMVER)
+            endif()
             set_target_properties(zlib PROPERTIES LINK_FLAGS
                 "-Wl,--version-script,\"${CMAKE_CURRENT_SOURCE_DIR}/zlib${SUFFIX}.map\"")
         else()

configure

@@ -562,6 +562,22 @@ else
   esac
 fi
 
+# Symbol versioning
+case "$uname" in
+  CYGWIN* | Cygwin* | cygwin* | MINGW* | mingw* | MSYS* | msys* | Darwin* | darwin*)
+    echo "Checking for Symbol versioning... No."
+  ;;
+  *)
+    if test $shared -eq 1; then
+      echo "Checking for Symbol versioning... Yes."
+      CFLAGS="${CFLAGS} -DHAVE_SYMVER"
+      SFLAGS="${SFLAGS} -DHAVE_SYMVER"
+    else
+      echo "Checking for Symbol versioning... No."
+    fi
+  ;;
+esac
+
 # Simplify some later conditionals
 case "$uname" in
 Linux* | linux*)
@@ -2019,6 +2035,7 @@ EOF
     ;;
 esac
 
+echo "Uname: $uname"
 echo "ARCH: ${ARCH}"
 echo "Using arch directory: ${ARCHDIR}"
 echo "Architecture-specific static object files:${ARCH_STATIC_OBJS}"

zbuild.h

@@ -124,6 +124,20 @@
 #  define Z_INTERNAL
 #endif
 
+/* Symbol versioning helpers, allowing multiple versions of a function to exist.
+ * Functions using this must also be added to zlib-ng.map for each version.
+ * Double @@ means this is the default for newly compiled applications to link against.
+ * Single @ means this is kept for backwards compatibility.
+ * This is only used for Zlib-ng native API, and only on platforms supporting this.
+ */
+#if defined(HAVE_SYMVER)
+#  define ZSYMVER(func,alias,ver) __asm__(".symver " func ", " alias "@ZLIB_NG_" ver);
+#  define ZSYMVER_DEF(func,alias,ver) __asm__(".symver " func ", " alias "@@ZLIB_NG_" ver);
+#else
+#  define ZSYMVER(func,alias,ver)
+#  define ZSYMVER_DEF(func,alias,ver)
+#endif
+
 #ifndef __cplusplus
 #  define Z_REGISTER register
 #else