On Sat, Aug 27, 2022 at 2:49 AM Edward Humes <aurxenon@xxxxxxxxx> wrote:
>
> Previously, R_ALPHA_LITERAL relocations would overflow for large kernel
> modules.
>
> This was because the Alpha's apply_relocate_add was relying on the kernel's
> module loader to have sorted the GOT towards the very end of the module as it
> was mapped into memory in order to correctly assign the global pointer. While
> this behavior would mostly work fine for small kernel modules, this approach
> would overflow on kernel modules with large GOT's since the global pointer
> would be very far away from the GOT, and thus, certain entries would be out of
> range.
>
> This patch fixes this by instead using the Tru64 behavior of assigning the
> global pointer to be 32KB away from the start of the GOT. The change made
> in this patch won't work for multi-GOT kernel modules as it makes the
> assumption the module only has one GOT located at the beginning of .got,
> although for the vast majority kernel modules, this should be fine. Of the
> kernel modules that would previously result in a relocation error, none of
> them, even modules like nouveau, have even come close to filling up a single
> GOT, and they've all worked fine under this patch.
>
> Signed-off-by: Edward Humes <aurxenon@xxxxxxxxx>
> ---
> arch/alpha/kernel/module.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/arch/alpha/kernel/module.c b/arch/alpha/kernel/module.c
> index 5b60c248de9e..cbefa5a77384 100644
> --- a/arch/alpha/kernel/module.c
> +++ b/arch/alpha/kernel/module.c
> @@ -146,10 +146,8 @@ apply_relocate_add(Elf64_Shdr *sechdrs, const char *strtab,
> base = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr;
> symtab = (Elf64_Sym *)sechdrs[symindex].sh_addr;
>
> - /* The small sections were sorted to the end of the segment.
> - The following should definitely cover them. */
> - gp = (u64)me->core_layout.base + me->core_layout.size - 0x8000;
> got = sechdrs[me->arch.gotsecindex].sh_addr;
> + gp = got + 0x8000;
>
> for (i = 0; i < n; i++) {
> unsigned long r_sym = ELF64_R_SYM (rela[i].r_info);
> --
> 2.34.1
>
Thanks for the patch! This was included in my pull request today and
is now upstream in Linus' tree.
