Re: Global constructors

[Jim Wilson <wilson at specifixinc dot com>]

Tiago Stein D'Agostini wrote:
> But I need to make it to call the global constructors (a call to it just 
> before call to main). Unfortunatelly I am not able to put a call to __do_global_ctors_aux (LD indicates an undefined 
> reference) even the __do_global_ctors_aux being there at the object file.

You aren't supposed to call this function.  You are only supposed to 
call __do_global_ctors.  __do_global_ctors then calls __do_global_ctors_aux.

There are multiple ways to support static constructors.  You can 
configure this for you port which ever way you would like it.  The best 
bet is to probably pick an existing target and model your port after it.

For a normal ELF target, the .init section contains code that is 
executed by the program loader when the code is loaded into memory, 
before calling main.  The .fini section contains code that is executed 
by the program loader after the program exits.  The addresses of static 
constructor/destructor functions are put in the .ctors/.dtors sections 
respectively, and the .init/.fini sections just have code to call each 
function in turn until it gets to the end of the section.  You need 
crti.o/crtn.o files that provide the function prologues/epilogues for 
the .init/.fini sections.  Gcc provides the rest of the code that goes 
in the .init/.fini sections via crtbegin.o/crtend.o.

If your loader doesn't automatically run the .init/.fini sections, which 
is common in embedded systems, then you can put code in the crt0.o file 
to run them.  In your crti.o file, put labels at the start of the 
.init/.fini sections.  You can then call the function in the .init 
section before calling main.  You can then call atexit to register the 
function in the .fini section to be called when the program exits.

If this seems like too much work, you can tell gcc not to use 
.init/.fini sections, in which case you need an explicit call to 
__do_global_ctors someplace.  You can do this yourself in the crt0.o 
startup code, or you can get gcc to emit a call to __main in the main 
function which does it for you.
--
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com