32-bit powerpc's elf_reloc_internal has no support for R_PPC_JMP_SLOT but clang with devel/powerpc64-binutils uses such for building kernel modules

[Justin Hibbits]

On Thu, Jun 6, 2019 at 8:06 PM Mark Millard via freebsd-ppc
<freebsd-ppc at freebsd.org> wrote:
>
>
> /usr/src/sys/powerpc/powerpc/elf64_machdep.c has:
>
> static int
> elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,
>     int type, int local, elf_lookup_fn lookup)
> {
> . . .
>         case R_PPC_JMP_SLOT:    /* function descriptor copy */
>                 lookup(lf, symidx, 1, &addr);
> #if !defined(_CALL_ELF) || _CALL_ELF == 1
>                 memcpy(where, (Elf_Addr *)addr, 3*sizeof(Elf_Addr));
> #else
>                 *where = addr;
> #endif
>                 __asm __volatile("dcbst 0,%0; sync" :: "r"(where) : "memory");
>                 break;
>
> . . .
>
> But /usr/src/sys/powerpc/powerpc/elf32_machdep.c 's elf_reloc_internal
> does not have any R_PPC_JMP_SLOT case in its code.
>
> Yet, from using clang as the system compiler for targeting 32-bit powerpc,
> readelf -asW /boot/kernel/if_gem.ko shows the likes of:
>
> Relocation section with addend (.rela.plt):
> r_offset r_info   r_type              st_value st_name + r_addend
> 00018328 00000215 R_PPC_JMP_SLOT      00000000 if_maddr_runlock + 0
> 00018330 00000315 R_PPC_JMP_SLOT      00000000 mii_mediachg + 0
> 00018338 00000415 R_PPC_JMP_SLOT      00000000 m_freem + 0
> 00018340 00000515 R_PPC_JMP_SLOT      00000000 device_get_softc + 0
> 00018348 00000715 R_PPC_JMP_SLOT      00000000 device_set_desc + 0
> 00018350 00000815 R_PPC_JMP_SLOT      00000000 printf + 0
> 00018358 00000b15 R_PPC_JMP_SLOT      00000000 ether_crc32_le + 0
> 00018360 00000e15 R_PPC_JMP_SLOT      00000000 bpf_mtap + 0
> . . .
>
> # file /boot/kernel/if_gem.ko
> /boot/kernel/if_gem.ko: ELF 32-bit MSB shared object, PowerPC or cisco 4500, version 1 (FreeBSD), dynamically linked, BuildID[sha1]=013a358835fddcd6bbb82d35a6ce36243eccb743, not stripped
>
> So, naturally, module loading such (manual or automatic)
> is a problem for the 32-bit powerpc context.
>
> The context was head -r347549 .
>
> ===
> Mark Millard
> marklmi at yahoo.com
> ( dsl-only.net went
> away in early 2018-Mar)

Can you try this patch?  Untested, just compiled.  It's essentially a
copy of the ELFv2 part of the elf64_machdep bit you posted above.

- Justin

diff --git a/sys/powerpc/powerpc/elf32_machdep.c
b/sys/powerpc/powerpc/elf32_machdep.c
index 11c14671d0b..219a61363cd 100644
--- a/sys/powerpc/powerpc/elf32_machdep.c
+++ b/sys/powerpc/powerpc/elf32_machdep.c
@@ -295,6 +295,12 @@ elf_reloc_internal(linker_file_t lf, Elf_Addr
relocbase, const void *data,
                *where = elf_relocaddr(lf, relocbase + addend);
                break;

+       case R_PPC_JMP_SLOT:
+               lookup(lf, symidx, 1, &addr);
+               *where = addr;
+               __asm __volatile("dcbst 0,%0; sync" :: "r"(where) : "memory");
+               break;
+
        default:
                printf("kldload: unexpected relocation type %d\n",
                    (int) rtype);