Dynamic loader

[Marco Gerards]

Hi,

As I mentioned earlier I am working on loadable module support for the
PPC.  I had a lot of problems with this so I decided to play a bit
with grub-emu to see what is going on.

At the moment this is still a big hack (and a few minutes work), if
Thomas does not mind I will make it work properly.

I found a big problem in kern/dl.c.  Two pointers are added and GRUB
is writing outside memory reserved for it, if I understand it
correctly.  I really hope Okuji can have a look at this and tell me
what is going on.  I am not familiar with this code and I am afraid it
can take a while to understand what is going on for me.

In `grub_dl_resolve_symbols' the following things are done:

In the case STT_FUNC the `sym->st_value' has a valid pointer.  After
that the following thing happens:

          sym->st_value += (Elf_Addr) grub_dl_get_section_addr (mod,
                                                                sym->st_shndx);

Another (valid) pointer gets added.  This results in an invalid
pointer which is used afterwards.  I think this happens consistently
and that is why nothing seems wrong when using GRUB.  In grub-emu this
simply means a segfault.  This segfault happens when `mod->init' is
called, which points to a non-executable region of memory.

When I reserve a lot (100 MB is what I used) of memory using mmap and
make sure it is executable it works because the memory that was
accidently used was allocated.

Any kind of help is appreciated.

Thanks,
Marco