What is 'DW_CFA_GNU_args_size'?

[Tatsuhiko Matsukawa]

I'm now developing a debugger(not GDB) for embeded controller which is 
 supported by GCC. I have a question about the interpretation of
 '.debug_frame' section of DWARF2 debugging information.
Please help me.

[Question]

There are 'DW_CFA_GNU_args_size' instructions in '.debug_frame' section.
It seems that this is GNU-extention.
I can't find the information about this.
Please tell me where the documentation about this is.

Thank you in advance.

     Tatsuhiko Matsukawa