| Message ID | 54BFD7A5.5080603@freebsd.org |
|---|---|
| State | Superseded |
| Headers | show |
On Wed, 2015-01-21 at 08:45 -0800, Nathan Whitehorn wrote: > The attached patch fixes the big-endian ELF64 loader in skiboot to > handle the fact that the ELF entry point is specified to point to a > function descriptor describing the entry point rather than the entry > point itself. (I haven't set it up to load the TOC base pointer though) > This is required to load the FreeBSD kernel as a skiboot payload. The > patch does not touch the little-endian loader since I'm not sure if the > ELFv2 spec still has function descriptors or not. An additional problem is that the Linux 64-bit BE kernel vmlinux doesn't have a correct function descriptor as an entry point :-( So that patch breaks loading a raw BE vmlinux... We probably need a quirk to recognize such an image, possibly via the fact that the value that would be in the function descriptor cannot possibly be a valid entry point as part of the image. As for LE, there are no descriptors. Cheers, Ben. > -Nathan > _______________________________________________ > Skiboot mailing list > Skiboot@lists.ozlabs.org > https://lists.ozlabs.org/listinfo/skiboot
On 01/22/15 09:02, Benjamin Herrenschmidt wrote: > On Wed, 2015-01-21 at 08:45 -0800, Nathan Whitehorn wrote: >> The attached patch fixes the big-endian ELF64 loader in skiboot to >> handle the fact that the ELF entry point is specified to point to a >> function descriptor describing the entry point rather than the entry >> point itself. (I haven't set it up to load the TOC base pointer though) >> This is required to load the FreeBSD kernel as a skiboot payload. The >> patch does not touch the little-endian loader since I'm not sure if the >> ELFv2 spec still has function descriptors or not. > An additional problem is that the Linux 64-bit BE kernel vmlinux doesn't > have a correct function descriptor as an entry point :-( So that patch > breaks loading a raw BE vmlinux... We probably need a quirk to recognize > such an image, possibly via the fact that the value that would be in the > function descriptor cannot possibly be a valid entry point as part of > the image. That's unfortunate. Seeing if the descriptor points into an ELF segment marked executable or not shouldn't be that bad, though. I can get coded up soon. An alternative would be to change the FreeBSD kernel's entry point so that it behaves like Linux, but I would prefer not to do that if possible since it could be an upgrade headache for our users. > As for LE, there are no descriptors. OK. The LE ABI seems to have removing all the "weirdness" from ppc64 that it can, so that's what I suspected might be the case. -Nathan > > Cheers, > Ben. > >> -Nathan >> _______________________________________________ >> Skiboot mailing list >> Skiboot@lists.ozlabs.org >> https://lists.ozlabs.org/listinfo/skiboot >
diff --git a/core/init.c b/core/init.c index 2c7e30c..6b794ec 100644 --- a/core/init.c +++ b/core/init.c @@ -143,8 +143,10 @@ static bool try_load_elf64(struct elf_hdr *header) (ph->p_vaddr + ph->p_memsz) < kh->e_entry) continue; - /* Get our entry */ - kernel_entry = kh->e_entry - ph->p_vaddr + ph->p_offset; + /* Get our entry: note the function descriptor dereference */ + kernel_entry = *(uint64_t *)(kh->e_entry - ph->p_vaddr + + ph->p_offset + load_base); + kernel_entry = kernel_entry - ph->p_vaddr + ph->p_offset; break; }