[GCC-XML] GCC backend upgrade

[Alex Leach]

Dear Brad / list,

Long story short, I thought I'd have a go at upgrading GCCXML's backend  
compiler to GCC4.7.2. I made a fork on github a week ago and have been  
working on it since.

I initially thought that there was no chance of me getting it to work, but  
I stuck at it and have had some joy, sort of. Parse-able XML output is  
being dumped, but there are some errors reported by the backend compiler.  
gccxml_cc1plus exits with code 1, and gccxml assumes that it seg-faulted,  
so all the ctests currently fail..

The last error I've come across has stumped me.. When looking for a  
solution online, I found a thread in this mailing list  
(http://public.kitware.com/pipermail/gccxml/2008-April/001100.html), where  
you resolved the issue within 24 hours - Kudos for that Brad!

On github, I found the commit to workaround this:
https://github.com/gccxml/gccxml/commit/36c88f006a8e81261e637869b985332308ac99dd

But tbh, I don't have a clue how to implement a similar fix for GCC 4.7.2.

The tracebacks only seem to show include lines and errors within system  
headers, which is new to me and makes debugging it a problem...

For example:

In file included from  
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/ios:43:0,
                  from  
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/ostream:40,
                  from  
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/iostream:40,
                  from ../GCC_XML/GXFront/gxSystemTools.h:29,
                  from ../GCC_XML/GXFront/gxConfiguration.h:20,
                  from ../GCC_XML/Testing/TestUsualInclude.cxx:1:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/ios_base.h:791:5:  
error: 'std::ios_base& std::ios_base::operator=(const std::ios_base&)' is  
private
In file included from  
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/ios:45:0,
                  from  
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/ostream:40,
                  from  
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/iostream:40,
                  from ../GCC_XML/GXFront/gxSystemTools.h:29,
                  from ../GCC_XML/GXFront/gxConfiguration.h:20,
                  from ../GCC_XML/Testing/TestUsualInclude.cxx:1:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/basic_ios.h:64:11:  
error: within this context
In file included from  
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/iostream:41:0,
                  from ../GCC_XML/GXFront/gxSystemTools.h:29,
                  from ../GCC_XML/GXFront/gxConfiguration.h:20,
                  from ../GCC_XML/Testing/TestUsualInclude.cxx:1:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/istream:  
In member function 'std::basic_istream<char>&  
std::basic_istream<char>::operator=(const std::basic_istream<char>&)':
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/istream:56:11:  
note: synthesized method 'std::basic_ios<char>&  
std::basic_ios<char>::operator=(const std::basic_ios<char>&)' first  
required here


--------------------------------


There are similar errors with std::basic_ofstream, std::basic_streambuf,  
std::locale::facet, std::num_put, and std::ctype. All giving errors about  
copy constructors on private members.

I suspect this has to do with a change in the C++03 standard, judging by  
this answer on SO: http://stackoverflow.com/a/9123195/566098

If you could suggest on which files I should direct my efforts, I'll do my  
best to resolve this. Any help would be really appreciated! Otherwise,  
I'll spend some time grep'ing and preprocessing various source files.. Any  
ideas?

--------------------------------

Changes I made are in a fork of your repo on github, hosted at  
https://github.com/alexleach/gccxml/

The changes are split over a few commits, as changing the GCC code  
affected almost 3,000 files, so I dumped that in a single commit and any  
manual edits and patches were committed afterwards. Should have probably  
started a branch...

Most of the work involved editing the CMake build system files. I saw that  
you're a core CMake maintainer, so I apologise if my edits aren't up to  
your usual standards!

---------------------------------

Unrelated to these issues, but thinking about moving forward.. Richard  
Guenther - one of the lead maintainers of the GCC project - suggested to  
me on IRC the other day that I might try and turn it into a plugin...

Plugins seem to be compatible with GCC versions 4.5 and up. I thought it  
sounds like a good idea, in that it would hopefully drop the need for a  
lot of the support headers; I imagine it should reduce future maintenance;  
the binary is much smaller; and obviously compiling a dynamically loaded  
plugin is much, much quicker than recompiling a large chunk of GCC.

So after getting the above issues - which I think are totally resolvable -  
I started working on patching xml.c to become a plugin. Obviously there's  
some issues with the global variables and functions patched into other  
modules, like in method.c, decl2.c and diagnostic.c, but the hard part is  
already done; you did it years ago!

I should probably create a fork for the plugin, but so far, I've just  
created a new sub-project (GCC/gccxml-plugin) in which I'm hacking xml.c  
in an attempt to turn it into a plugin. Still quite a lot of work to do;  
I'm a noob with C and C++ so progress is slow, but I'm learning a lot!  
Would also need to modify the gccxml driver to instead invoke g++, also  
passing it different arguments; i.e: '-fplugin=libgccxml_plugin.so  
-fplugin-libgccxml_plugin-xml=... -fplugin-libgccxml_plugin-xml_start=...'


---------

Thanks for reading this! I was indenting on submitting a Pull Request at  
some point, but I feel like I've made a mess of what was beautiful code  
and a clean version history, so maybe it's best left as a separate fork..

If you would be interested in merging any of it back into the main  
repository, please let me know and I'll make a Pull Request. I think I  
should get it working first, though...

One last thing worth mentioning. I had a look at the other fork, by Andrej  
Mitrovic, and incorporated some of his feature additions, like putting C++  
attributes into XML tags and detection of Pod, Anon and TypeScoped C++  
Types.

Yours sincerely,
Alex