On Fri, 25 Jul 2008 16:33:56 +0200 kenneth johansson <[EMAIL PROTECTED]> wrote:
> On Fri, 2008-07-25 at 14:19 +0200, Haavard Skinnemoen wrote: > > On Fri, 25 Jul 2008 13:55:58 +0200 > > kenneth johansson <[EMAIL PROTECTED]> wrote: > > > > > > An ELF shared library has the dynamic relocations we need. So if we > > > > build u-boot as an .so file, it should work in theory on most > > > > architectures. > > > > > > well the elf binary of u-boot obviously has everything we need > > > regardless of what options it was compiled with. If we had a full linker > > > at runtime we could just do a relink to whatever address we wanted. > > > > No we couldn't if we don't have any relocation information. Just as you > > can't relink just any ELF binary to run at a different location after > > it's been through a final link, no matter how "full" the linker is. > > Take time and READ what people write. I wrote compiler option and you go > on about some final link that removes the relocation information. My > point was that it is irrelevant if you use pic shared whatever if you > are going to use the elf relocation information anyway granted you have > less work to do if the object was compiled as PIC. Oh, you're talking about some hypothetical u-boot binary that hasn't been through the linker? How exactly do you generate it? Besides, I talked about compiler options too (in the paragraph you cut out). If you don't compile the code with -fPIC, most linkers won't be able to make the result relocatable no matter what options you specify. > > > It sounds a bit easier to just loop over a list of pointers and change > > > the values than to implement a complete linker but maybe that is just > > > me. > > > > The question remains how should that list of pointers be generated? One > > possible answer is to let the linker do it (as dynamic relocations). > > Since I have not done a linker I probably miss some information on what > makes the dynamic relocations so special ?? Yes, you probably do. Dynamic relocations are quite special as they are intended for the _runtime_ system, not the linker. Therefore, they are included in a loadable segment so that the program itself or the dynamic loader can go through them and perform fixups at runtime. Also, most platforms only allow a small handful of relocation types to be used as dynamic relocations. This makes the job of the dynamic loader much easier than that of the linker. > And could you outline how the last step in generating the binary image > would work. That's basically the question I've been trying to ask for some time. On PowerPC, I assume -mrelocatable does the trick. On other platforms, I just don't know. > now it works as follows. One final static link with all the .a files and > a specified start address for TEXT. result is a elf file with al symbols > resolved adn it can be relinked to another address if one wants but we > use objcopy to make a binary. Have you ever _tried_ to relink the final u-boot ELF file to another address? How do you do that? > here is a patch to generate dynamic relocations in the elf file. What is > the next step? objcopy -j .rela.dyn -O binary u-boot dyn_reloc_table ?? Might actually work, though we might need more linker options as well. At least -Bsymbolic comes to mind. And I'm not sure if -Bstatic goes well along with -shared... In any case, there's no next step. The dynamic relocations are included in a loadable segment, so they will end up in the .bin file after the last objcopy step. There will obviously be a fair amount of arch-specific code required to make the actual relocation work though. Haavard ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ U-Boot-Users mailing list U-Boot-Users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/u-boot-users
