Alan Modra <amo...@gmail.com> wrote on 2010/10/11 14:58:45:
>
> On Sun, Oct 10, 2010 at 11:20:06AM +0200, Joakim Tjernlund wrote:
> > Now I have had a closer look at this and it looks much like -fpic
> > on ppc32, you still use the GOT/TOC to load the address where the data is.
>
> No, with ppc64 -mcmodel=medium you use the GOT/TOC pointer plus an
> offset to address local data.
I guess I have to look closer then.
>
> > I was looking for true %pc relative addressing of data. I guess this is
> > really
> > hard on PowerPC?
>
> Yes, PowerPC lacks pc-relative instructions.
>
> > I am not sure this is all it takes to make -fpic to work with -mrelocatable,
> > any ideas?
>
> You might be lucky. With -mrelocatable, .got2 only contains
> addresses. No other constants. So a simple run-time loader can
> relocate the entire .got2 section, plus those locations specified in
> .fixup. You'll have to make sure gcc does the same for .got, and your
> run-time loader will need to be modified to handle .got (watch out for
> the .got header!).
yes, almost there. I have this reloc routine:
#define GOT(NAME) NAME ## @got (r30)
* Adjust got pointers, no need to check for 0, this code
* already puts a few entries in the table.
*/
li r0,__got_entr...@sectoff@l
la r3,GOT(_GOT_TABLE_)
lwz r11,GOT(_GOT_TABLE_)
mtctr r0
sub r11,r3,r11
addi r3,r3,-4
1: lwzu r0,4(r3)
cmpwi r0,0
beq- 2f
add r0,r0,r11
stw r0,0(r3)
2: bdnz 1b
Linker script:
.reloc :
{
_GOT_TABLE_ = .;
*(.got)
_GOT2_TABLE_ = .;
*(.got2)
_FIXUP_TABLE_ = .;
*(.fixup)
}
The above depends on that the first entry in the got to
which _GOT_TABLE_ points, has an entry to itself.
Using -fPIC I could create such an entry but I cannot find a way
to do it using -fpic. Any ideas?
Jocke
