Gabriel Paubert <paub...@iram.es> wrote on 2010/10/06 10:15:26: > > On Tue, Oct 05, 2010 at 10:55:36PM +0200, Joakim Tjernlund wrote: > > Richard Henderson <r...@redhat.com> wrote on 2010/10/05 20:56:55: > > > > > > On 10/05/2010 06:54 AM, Joakim Tjernlund wrote: > > > > Ian Lance Taylor <i...@google.com> wrote on 2010/10/05 15:47:38: > > > >> Joakim Tjernlund <joakim.tjernl...@transmode.se> writes:
> > You can get at the GOT table using PC relative addressing so why not > > strings or data in a similar fashion? > > Because you access the got with a single (16 bit offset) instructions. > If you add .rodata, .data and .bss, you will likely overflow it > quite rapidly. > > Did you look at -mrelocatable? Yes, u-boot currently uses -mrelocatable. > > I don't know whether it can solve all your problems (probably not), > and there are regular threats of removing it, or at least there > were, since I see that the documentation was much improved in August. I really wish mrelocatable is added to all archs. The normal ELF relocs are too big to fit well in u-boot. > > Anyway, I used it a decade ago to write a bootloader that: > > a) was loaded at an unpredictable and unconfigurable address > depending on the mood of the firmware (really, it depended at > least on the media from which you booted, even exactly the > same binary image) That is pretty much what I am trying to do. > > b) the first thing the bootloader did was to run the relocation code > for the adress at which it had been loaded by the firmware and > find the free memory areas from tables provided by the firmware. > The code in this part could not use any global pointer variable, > AFAIR, but it was short. Right, but here u-boot is still in flash and cannot write/relocate the GOT. Later, when RAM is setup, it moves to RAM and relocates the GOT. I have managed to do this but this required each access to global data(including string literals) to be wrapped by a LINK_OFF(ptr) function that calculated the offset between link and run address and adjusted the ptr accordinly. This is unmaintainable though so the patch wasn't accepted by u-boot. Jocke
