Re: Grub for ia64 - function descriptors

["Hollis Blanchard" <hollis@penguinppc.org>]

On Mon, 02 Oct 2006 08:31:10 +0200, tgingold@free.fr said:
> Quoting Hollis Blanchard <hollis@penguinppc.org>:
> 
> > On Fri, 2006-09-29 at 08:59 +0200, tgingold@free.fr wrote:
> > > Quoting Hollis Blanchard <hollis@penguinppc.org>:
> > >
> > > > On Thu, 2006-09-28 at 15:45 +0200, tgingold@free.fr wrote:
> > > > >
> > > > >           if (grub_strcmp (name, "grub_mod_init") == 0)
> > > > >             mod->init = (void (*) (grub_dl_t)) sym->st_value;
> > > > >
> > > > > This won't work on ia64 AFAIK.
> > > >
> > > > Can't this problem be solved with an architecture-specific macro?
> > > >
> > > > FWIW, 64-bit PowerPC also uses function descriptors. They look something
> > > > like:
> > > >         long code_address
> > > >         long table_of_contents
> > > >         long unused
> > > >
> > > > The table_of_contents (TOC) value needs to be placed into r2 when
> > > > jumping at code_address (and of course the old one needs to be restored
> > > > when returning).
> > > Indeed, same issue.
> > >
> > > >I assume IA64 is similar here, and given that, a
> > > > module_jump function implemented in assembly by each architecture would
> > > > solve this problem.
> > > I'd prefer modules to export pointers. Seems to be easier to deal.
> >
> > I don't know what you mean; please elaborate (with pseudo-code if
> > possible).
> 
> I'd propose modules export struct grub_dl.  This struct contains init and
> fini
> functions pointers.
> Getting the address of a data structure is much more portable.
> Dealing with function pointers would be a matter of the relocator.

It looks like this is only done twice in the current code: mod->init and
mod->fini. Wouldn't it be easy to do this:
--- kern/dl.c   28 May 2006 23:01:43 -0000      1.12
+++ kern/dl.c   3 Oct 2006 02:15:51 -0000
@@ -380,9 +380,9 @@ grub_dl_resolve_symbols (grub_dl_t mod,
              return grub_errno;

          if (grub_strcmp (name, "grub_mod_init") == 0)
-           mod->init = (void (*) (grub_dl_t)) sym->st_value;
+           mod->init = grub_dl_arch_func (sym->st_value);
          else if (grub_strcmp (name, "grub_mod_fini") == 0)
-           mod->fini = (void (*) (void)) sym->st_value;
+           mod->fini = grub_dl_arch_func (sym->st_value);
          break;

        case STT_SECTION:

-Hollis