Exporting Symbols

Some ports limit the exported symbols. We need to mark API symbols as exported when we use it outside the library. Since WebKit consists of a set of libraries (WTF, JavaScriptCore, WebCore, WebKit), each library need to export symbols if the API is used from a different library.

There is two primary way to export symbols: export lists and inline annotations. Some ports use export lists. others use inline annotations, or even both.

Export Lists

An export list is a text file which contains the list of exporting symbols. Linkers refer these files to decide which symbols should be exported.

Ports have their own separate lists:

• trunk/Source/WebCore/WebCore.exp.in
  • Mac port uses this to build WebCore.framework.

• trunk/Source/autotools/symbols.filter
  • GTK port uses this to build libwebkitgtk.so
• trunk/Source/WebKit2/mac/WebKit2.order
  • Mac WebKi2 port uses this to build WebKit2.framework
• trunk/Source/WebKit/WebKit.vcxproj/WebKitExportGenerator/WebKitExports.def.in
  • Will be used by Apple Win when switching to VS2010.

Inline Annotations

Inline annotations is compiler-specific qualifiers which are encapsulated by a set of macros. These macros are defined in following files:

• trunk/Source/WTF/wtf/ExportMacros.h​
  • WTF_EXPORT_PRIVATE
• trunk/Source/JavaScriptCore/runtime/JSExportMacros.h​
  • JS_EXPORT_PRIVATE, JS_EXPORTDATA
• trunk/Source/WebCore/platform/PlatformExportMacros.h​

• (TODO: List port specific definitions for WebKit API layer here.)

Inline annotations are adopted as following:

• Mac port uses WTF_EXPORT, WTF_EXPORT_PRIVATE, JS_EXPORT, JS_EXPORT_PRIVATE, JS_EXPORTDATA to export WTF and JSC symbols.
• Win ports use it JS_EXPORTDATA for exporting JSC static variables.
• Many port have use their own inline annotations to export their WebKit API.

Caveat

• You cannot export inline function.
• If you need to export C++ vtables (that rarely happens though), you need to add JS_EXPORT_PRIVATE or WTF_EXPORT_PRIVATE to the class definition.

How can I export my symbols?

Here are some typical scenarios when you need to care about symbol export:

Exporting WebCore symbols to use them from port WebKit implementations

• If you use it from Mac(WK1), you need to edit WebCore.exp.in.
• Otherwise you don't need to do anything about symbols.

Exporting JavaScriptCore/WTF symbols to use them from port WebCore

• You need to edit JavaScriptCore.def
• You need to add JS_EXPORT_PRIVATE or WTF_EXPORT_PRIVATE to the function.

Exporting WebCore symbols to use them from Internals object (WebCoreTestSupport)

• Only WebCore symbols need to be exported which are used in Internals (if not already exported. Check previous definitions first)
• Internals symbols need not be exported.

For WTF/JavaScriptCore symbols,

• You need to edit JavaScriptCore.def.
• You also need to add JS_EXPORT_PRIVATE or WTF_EXPORT_PRIVATE to exporting functions.

For WebCore symbols, you need to edit following files...

• WebCore.exp.in, symbols.filter, WebKit2.order

Exporting WTF/JavaScriptCore/WebCore symbols to use them from DumpRenderTree

• You shouldn't do it.
• If you inevitably need to do it, it's same as the Internals appraoch noted above.

Exporting WebKit API symbols to applications

TODO: Write port specific way to do this.