- Binary Compatability and wxWidgets
+ Binary Compatibility and wxWidgets
==================================
0. Purpose
----------
-This is broad technote covering all aspects of binary compatability with
+This is a broad technote covering all aspects of binary compatibility with
wxWidgets.
1. Releases
-----------
-General overview of releases can be found in tn0012.txt, but for
+General overview of releases can be found in tn0012.txt, but for
completeness the wxWidgets release version number is as follows:
2.6.2
(I.E. Major.Minor.Release).
-All Release versions where the Minor is EVEN (2.4.x,2.6.x
-etc. ODD minors are development versions) are expected to be binary
-compatable. Note that this means FORWARD binary compatability only -
-new methods to classes are ok as long as they arn't virtual, etc.
+All versions with EVEN minor version component (e.g. 2.4.x, 2.6.x etc.)
+are expected to be binary compatible (ODD minors are development versions
+and the compatibility constraints don't apply to them). Note that by
+preserving binary compatibility we mean BACKWARDS compatibility only,
+meaning that applications built with old wxWidgets headers should continue
+to work with new wxWidgets (shared/dynamic) libraries without the need to
+rebuild. There is no requirement to preserve compatibility in the other
+direction (i.e. make new headers compatible with old libraries) as this
+would preclude any additions whatsoever to the stable branch. But see
+also section (4).
-2. What kind of changes are NOT binary compatable
+
+2. What kind of changes are NOT binary compatible
-------------------------------------------------
If its still up, the KDE guide is a good reference:
-http://developer.kde.org/documentation/other/binarycompatibility.html
+http://techbase.kde.org/Policies/Binary_Compatibility_Issues_With_C++
-The changes that are NOT binary compatable:
+The changes that are NOT binary compatible:
- Adding a virtual function
- Changing the name of a any function or variable
-- Changing the signature of a virtual function (adding a parameter,
+- Changing the signature of a virtual function (adding a parameter,
even a default one)
- Changing the order of the virtual functions in a class
["switching" them, etc.]
-- Changing access privalages to a function (protected to private etc.)
-[unlike KDE we need to support windows so this is not allowed]
+- Changing access privileges of a function: some compilers (among which MSVC)
+ use the function access specifier in its mangled name. Moreover, while
+ changing a private function to public should be compatible (as the old
+ symbol can't be referenced from outside the library anyhow), changing a
+ virtual private function to public is NOT compatible because the old symbol
+ is referenced by the virtual tables in the executable code and so an old
+ program compiled with MSVC wouldn't start up with a new DLL even if it
+ doesn't use the affected symbol at all!
- Adding a member variable
- Changing the order of non-static member variables
-3. wxABI_VERSION and BACKWARD binary compatability
+3. Changes which are compatible
+-------------------------------
+
+- Adding a new class
+- Adding a new non-virtual method to an existing class
+- Adding a new constructor to an existing class
+- Overriding the implementation of an existing virtual function
+[this is considered to be backwards binary compatible until we find a
+ counter example; currently it's known to work with Apple gcc at least]
+- Anything which doesn't result in ABI change at all, e.g. adding new
+ macros, constants and, of course, private changes in the implementation
+
+
+4. wxABI_VERSION and "forward" binary compatibility
--------------------------------------------------
-As mentioned we do not support BACKWARD binary compatability.
+As mentioned we do not support "forward" binary compatibility, that is the
+ability to run applications compiled with new wxWidgets headers on systems
+with old wxWidgets libraries.
+
+However, for the developers who want to ensure that their application works
+with some fixed old wxWidgets version and doesn't (inadvertently) require
+features added in later releases, we provide the macro wxABI_VERSION which
+can be defined to restrict the API exported by wxWidgets headers to that of
+a fixed old release.
-However, for this purpose we have the macro wxABI_VERSION. All
-new symbols added to binary compatable releases are to be ifed
-with wxABI_VERSION.
+For this to work, all new symbols added to binary compatible releases must
+be #if'ed with wxABI_VERSION.
The layout of wxABI_VERSION is as follows:
2 06 02
Major Minor Release
-I.E. it corresponds to the wxWidgets release in {1}.
+I.E. it corresponds to the wxWidgets release in (1).
An example of using wxABI_VERSION is as follows for symbols
only in a 2.6.2 release:
//helpers for the wxPython people
bool LoadURI(const wxString& fileName)
{ return Load(wxURI(fileName)); }
-bool LoadURIWithProxy(const wxString& fileName, const wxString& proxy)
+bool LoadURIWithProxy(const wxString& fileName, const wxString& proxy)
{ return Load(wxURI(fileName), wxURI(proxy)); }
#endif
-4. Workarounds for adding virtual functions
+5. Workarounds for adding virtual functions
-------------------------------------------
-Originally the idea for adding virtual functions to binary compatable
+Originally the idea for adding virtual functions to binary compatible
releases was to pad out some empty "reserved" functions and then
rename those later when someone needed to add a virtual function.
To use wxShadowObject, you first call AddMethod or AddField with
the first parameter being the name of the field and/or method
-you want, and the second parameter being the value of the
+you want, and the second parameter being the value of the
field and/or method.
In the case of fields this is a void*, and in the case of method
typedef int (*wxShadowObjectMethod)(void*, void*);
After you add a field, you can set it via SetField with the same
-params as AddField, the second param being the value to set
+parameters as AddField, the second parameter being the value to set
the field to. You can get the field after you call AddField
via GetField, with the parameters as the other two field functions,
-only in the case the second parameter is the fallback
-value for the field in the case of it not being found in the
-hash map.
+only in the case the second parameter is the fallback
+value for the field in the case of it not being found in the
+hash map.
You can call a method after you add it via InvokeMethod, which
returns a bool indicating whether or not the method was found
in the hash map, and has 4 parameters. The first parameter is
the name of the method you wish to call, the second is the first
-parameter passed to the wxShadowObjectMethod, the third is the
+parameter passed to the wxShadowObjectMethod, the third is the
second parameter passed to that wxShadowObjectMethod, and the
fourth is the return value of the wxShadowObjectMethod.
-5. version-script.in
+6. version-script.in
--------------------
For ld/libtool we use sun-style version scripts. Basically
-anything which fits the conditions of being ifed via wxABI_VERSION
+anything which fits the conditions of being #if'ed via wxABI_VERSION
needs to go here also.
See 'info ld scripts version' on a GNU system, it's online here:
Where X is the current Release as mentioned earlier, i.e. 2. This
is following by an opening bracket "{", followed by "global:",
followed by patterns matching added symbols, then followed by "}", and then
-the file is either followed by earlier Releases or ended by
+the file is either followed by earlier Releases or ended by
a @WX_VERSION_TAG@ block without the period or Release.
The patterns used to specify added symbols are globbing patters and can
*wxLogBuffer*;
-5.5. Checking the version information in libraries and programs
----------------------------------------------------------------
+7. Checking the version information in libraries and programs
+-------------------------------------------------------------
On Sun there is a tool for this, see pvs(1). On GNU you can use objdump, below
are some examples.
00000000000abe10 g DF .text 0000000000000088 WXD_2.6.2 _ZN14wxZipFSHandler7CleanupEv
-6. Testing binary compatability between releases
+8. Testing binary compatibility between releases
------------------------------------------------
-An easy way of testing binary compatability is just to build wxWidgets
+An easy way of testing binary compatibility is just to build wxWidgets
in dll/dynamic library mode and then switch out the current library
in question with an earlier stable version of the library, then running
the application in question again. If it runs OK then there is usually
-binary compatability between those releases.
+binary compatibility between those releases.
You can also break into your debugger or whatever program you want
to use and check the memory layout of the class. If it is the same
-then it is binary compatable.
-
-Also remember to look at http://www.wxwidgets.org/bincompat.html page which
-summarizes the results of testing of all the samples built against old
-libraries headers with the new library binaries under Unix.
+then it is binary compatible.
+(In GDB the command x/d will show addresses as pointers to functions if
+possible so you can see if the order of the functions in vtbl doesn't change.)
+
+Another way to check for binary compatibility is to build wxWidgets in shared mode
+and use the 'abicheck.sh --generate' script before doing your changes to generate
+the current ABI (if the 'expected_abi' file is not already in the repo).
+Then rebuild wxWidgets with your changes and use 'abicheck.sh' to compare the
+resulting ABI with the expected one.
+Note that the abicheck.sh script is in the "lib" folder.
=== EOF ===
projects / wxWidgets.git / blobdiff