Getting started with GCC plugins - gcc

Question

So after searching the web for a while, Ive decided to try here as it seems to be a good forum for discussion. Im trying to create a simple gcc plugin. The program code is attached in the end of this mail, but in plain english it registers the plugin and makes sure that the pragma_init function is called when pragmas are registered. It is here that I use c_register_pragma to intercept some of the pragmas.
I compile it using the example in http://gcc.gnu.org/onlinedocs/gccint/Plugins-building.html#Plugins-building. The compilation and linking works fine. However, when I load the plug-in I get:
gcc -c -fplugin=plugin.so test.c -o test.o
cc1: error: cannot load plugin plugin.so
plugin.so: undefined symbol: warning
What am I doing wrong? In addition, when including some header files (that will be required later), I get a lot of errors. For example, including "tree.h" yields (amongst 50 other errors):
/machmode.h:262:1: error: unknown type name 'class'
class bit_field_mode_iterator
^
/machmode.h:263:1: error: expected '=', ',', ';', 'asm' or '__attribute__' before '{' token
{
^
/plugin/include/tree.h:27:0,
from conftest.c:63:
/vec.h:220:8: error: field 'register_overhead' declared as a function
Anyone have a clue on what I am doing wrong?
Thank you

Answer 1

There are two problems here :
The error : "cannot load plugin plugin.so" means that you should add to your LD_LIBRARY_PATH the directory where you store your new shared library plugin.
The hundreds of errors you got with all the files in the include are resolved in my computer if you compile with g++ instead of gcc (not sure to understand why thought)

Answer 2

Which version of GCC are you using, both to compile your plugin, and to use the plugin? Run simply
gcc -v
without any other program argument to find out!
Did you install the appropriate package for GCC plugin development (on Debian or Ubuntu, it might be gcc-4.7-plugin-dev, but adapt the 4.7 version to your particular version of GCC)?
Did you install all the dependencies needed to build your GCC (on Debian or Ubuntu, apt-get build-dep gcc-4.7 gcc-4.7-plugin-dev)?
Recent versions of GCC (notably many GCC 4.7 shipped by distributions, and all GCC 4.8) are compiled by a C++ compiler, not a C compiler.
You may check how was your GCC built (in C or in C++) by running
nm -D -C $(gcc -print-file-name=cc1)
If that command shows typed C++ manged names, e.g. execute_ipa_pass_list(opt_pass*) instead of just execute_ipa_pass_list your GCC has been compiled with a C++ compiler (probably g++)
So you may need to use g++ (not gcc) to compile your GCC plugin.
As I commented, did you consider using MELT (a domain specific language to extend GCC) to extend or customize your gcc compiler?
I suggest downloading the very latest http://gcc-melt.org/melt-plugin-snapshot.tar.bz2 since I will release the next MELT in a few weeks for GCC 4.7 and 4.8
And don't expect to change the parsing behavior of your GCC with a plugin. That is not really possible (GCC provides only plugin hooks to add your builtins and pragmas, not to extend the parsed syntax).