using plugin and lto: problem linking c-pragma symbol

[Pierre Vittet]

Hello,

I try to use the plugin pragma-plugin.c which is given in the testsuite 
(gcc/testsuite/g++.dg/plugin/pragma_plugin.c), I have compiled it as a 
shared library.

If I try it on a simple c file it works, however, if I use -flto it 
causes an error:

gcc -fplugin=./pragma_plugin.so -flto test.c

lto1: error: cannot load plugin ../pragma_plugin.so
../pragma_plugin.so: undefined symbol: c_register_pragma
lto-wrapper: /usr/bin/gcc returned 1 exit status
/usr/lib/gcc/i486-slackware-linux/4.7.0/../../../../i486-slackware-linux/bin/ld: 
lto-wrapper failed
collect2: error: ld returned 1 exit status

I don't know much about LTO but I guess it is important to be able to 
use langage specific function (such as c_register_pragma) in plugin even 
when using lto. I have this need in others plugins (I would like to have 
pragma support in MELT). Maybe a solution could be to define 
c_register_pragma and others related functions as weak references 
(however it mights not works for all plateform).

What would be the better way to patch this?

Pierre Vittet