[PATCH] ARM: module: fix unwind section relocation out of range error

[Kursad Oney]

Hi William,


On Fri, Sep 19, 2025 at 10:10 PM William Zhang
<william.zhang at broadcom.com> wrote:
>
> In an armv7 system that uses non-3G/1G split and with more than 512MB
> physical memory, driver load may fail with following error:
>    section 29 reloc 0 sym '': relocation 42 out of range (0xc2ab9be8 ->
> 0x7fad5998)
>
> This happens when relocation R_ARM_PREL31 from the unwind section
> .ARM.extab and .ARM.exidx are allocated from the VMALLOC space while
> .text section is from MODULES_VADDR space. It exceeds the +/-1GB
> relocation requirement of R_ARM_PREL31 hence triggers the error.
>
> The fix is to mark .ARM.extab and .ARM.exidx sections as executable so
> they can be allocated within .text section and always meet range
> requirement.

Not "within" .text, but "along with" or "in close proximity to".

>
> Co-developed-by: Ard Biesheuvel <ardb at kernel.org>
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> Signed-off-by: William Zhang <william.zhang at broadcom.com>

I think a Fixes tag might be appropriate?

>
> ---
>
>  arch/arm/kernel/module-plts.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
> index 354ce16d83cb..5f5bf5e63bd6 100644
> --- a/arch/arm/kernel/module-plts.c
> +++ b/arch/arm/kernel/module-plts.c
> @@ -225,6 +225,18 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
>                         mod->arch.init.plt = s;
>                 else if (s->sh_type == SHT_SYMTAB)
>                         syms = (Elf32_Sym *)s->sh_addr;
> +#if defined(CONFIG_ARM_UNWIND) && !defined(CONFIG_VMSPLIT_3G)
> +               else if (s->sh_type == ELF_SECTION_UNWIND ||
> +                        (strncmp(".ARM.extab", secstrings + s->sh_name, 10) == 0)) {
> +                       /*
> +                        * To avoid the possible relocation out of range issue for
> +                        * R_ARM_PREL31, mark unwind section .ARM.extab and .ARM.exidx as
> +                        * executable so they will be allocated within .text section to meet
> +                        * +/-1GB range requirement of the R_ARM_PREL31 relocation
> +                        */
> +                       s->sh_flags |= SHF_EXECINSTR;
> +               }
> +#endif
>         }
>
>         if (!mod->arch.core.plt || !mod->arch.init.plt) {
> --
> 2.43.7
>