[GCC-XML] gccxml and the latest GCC

[Alex Leach]

Hi,

On Tue, 18 Jun 2013 13:05:39 +0100, Brad King <brad.king at kitware.com>  
wrote:

> There is discussion about updating the internal parser here:
>
>  http://thread.gmane.org/gmane.comp.compilers.gccxml/658
>
> but AFAIK no progress has been made since then.

Yea, I've been meaning to get back to you about that... Sorry it's been so  
long; you've been very fast to respond yourself.

GCCXML backend upgrade status (to GCC 4.7.2)
---------------------------

So, I was testing on Linux and although I got everything to compile fine,  
I couldn't get past certain runtime errors. I recently applied the  
upgrades you made to the support headers, but I still couldn't get past  
runtime errors mentioning at least `size_type`.

I thought that it was a problem with the Support headers, but I felt  
completely out of my depth when reading them; I never read K&R's last  
section on compilers and I'm in the middle of writing my PhD thesis (in  
Biology!), so I'm afraid I didn't manage to complete the backend upgrade;  
I had to abort. I'm sure we could have figured it out together, but I just  
ran out of time...

However, I still felt the need to get gccxml working (well, pyplusplus  
really) on my system, so I recently spent some time getting GCCXML to work  
as a GCC plugin. I started this as a fork a while ago, so I just picked up  
where I left off really.

Keeping up with GCC versions
------------------

My system compiler was updated to GCC4.8 some time ago now, which is quite  
a major change from GCC 4.7, in that 4.8 now includes C++ code. The most  
notable difference, in terms of GCCXML's xml.c, is that the `VEC(tree,  
gc)*` macro is now a C++ vector: `vec<tree, va_gc>*`.

Upgrading GCCXML's internal compiler, from GCC 4.7 to 4.8 would again be  
quite a major upgrade. As I never got the GCC 4.7 backend to work, I  
figured it might be easier to keep up with GCC, if I turned `xml.c` into a  
GCC plugin.

So, that's what I did...


Plugin vs standalone gccxml
-----

As a plugin, its nowhere near as platform- and compiler-agnostic as the  
main gccxml. It can't, for example, behave as either Intel or Borland  
compilers. I also didn't have the confidence to spend my time updating the  
compiler driver in C i.e. the front-end `gccxml`, so I (stupidly) re-wrote  
it in Python, just so that pygccxml could use the command line arguments  
it expects to work (e.g. -fxml).

Getting it to work on Windows seems impossible at this time, without  
additional changes to GCC's build system, at least. Although it might be  
possible on Cygwin, MinGW does not support GCC plugins. Apparently,  
patches have been submitted to enable GCC plugins on Windows, but Andrej,  
who should be on this list, has said that even with these patches, he  
couldn't get past `./configure --enable-plugin`.

Upsides
-----

Wouldn't be right not to mention what's good about it! For one, it  
compiles a lot faster, as there's only two source files: xml.c and  
gccxml_plugin.c. It's a lot smaller too; when stripped, the plugin  
occupies 92Kb, whereas a debug build (-g3) compiled against a debug build  
of GCC occupies 1.3M. (cf. 232kB and 8.3M for stripped, system builds of  
gccxml and gccxml_cc1plus, respectively, from master).

---

I can't vouch that the results are identical to those produced by  
standalone gccxml, and I'm sure the plugin will be slower, but if you have  
GCC 4.8 on Linux, then it should be useful.

So, the GCCXML plugin (appears to) work for my purposes - I generated over  
2,000 Boost Python C++ source files with it and pyplusplus yesterday,  
which I'm afraid to say, I've failed to do with standalone gccxml and any  
GCC > 4.7.2. At the moment, I have the plugin working with GCC 4.8.0 and  
4.8.1 on x86_64 Linux, version 3.9.6.

It would require more work to compile against GCC 4.6 and 4.7, as I didn't  
wrap these preprocessor macros around all the modifications I made. i.e.

# if GCC_VERSION >= 4008
    vec<tree, va_gc>* ...
# else
    VEC(tree, gc)* ...
# endif

I'd hope GCC 4.6-7 would work with some more of these pre-processor  
macros, but I thought it might be a better idea to instead make separate  
tags for each minor GCC version > 4.6. Either way, I'm unlikely to do  
either in at least the next few months, as my thesis deadline is  
September(!).

---

All the work I've done on gccxml and the plugin has been committed on  
github. I'll make sure that's the case after sending this email, anyway..

GCCXML with the GCC-4.7.2 backend can be found here:  
https://github.com/alexleach/gccxml_plugin/tree/master
(in case you skipped above text, or I was unclear, this needs more work)

And the gccxml_plugin can be found here:  
https://github.com/alexleach/gccxml_plugin
(this works for me, with GCC 4.8.0-1 on Linux)


Brad, I'm sorry that the commit histories are a bit of a mess. You seem  
pretty damn good at keeping a clean git history; I've still got a lot to  
learn!

I hope that clarifies things, and the work helps someone else other than  
me!

If you've got any questions, please feel free to ask. I'll do my best to  
answer in a short space of time...

Kind regards,
Alex