Re: [PATCH] fix 3.16 unknown rela relocation 4 error

[Ben Hutchings]

On Sat, 2020-01-25 at 22:16 -0500, Woody Suwalski wrote:
> Trying to use an AMD64 3.16 kernel built on a new Debian system fails 
> because
> most of the kernel modules can not be loaded.

I don't recommend using the latest toolchain for 3.16 (certainly gcc 9
won't work).  But I will apply this since it's such a simple fix. 
Thanks for the backport.

Ben.

> This patch handles the PLT32 relocation errors for kernels modules built 
> with binutils
> newer then 2.31, similar to:
> [    5.742485] module: autofs4: Unknown rela relocation: 4
> [    5.742536] systemd[1]: Failed to insert module 'autofs4': Exec 
> format error
> 
> This patch is based on a mainline kernel patch 
> b21ebf2fb4cde1618915a97cc773e287ff49173e
> From: "H.J. Lu" <hjl.tools@xxxxxxxxx>
> Date: Wed, 7 Feb 2018 14:20:09 -0800
> Subject: x86: Treat R_X86_64_PLT32 as R_X86_64_PC32
> 
> Signed-off-by: Woody Suwalski <terraluna977@xxxxxxxxx>
> 
> --- a/arch/x86/tools/relocs.c    2020-01-24 18:48:09.477919152 -0500
> +++ b/arch/x86/tools/relocs.c    2020-01-24 18:48:53.645612045 -0500
> @@ -763,6 +763,7 @@ static int do_reloc64(struct section *se
>       switch (r_type) {
>       case R_X86_64_NONE:
>       case R_X86_64_PC32:
> +    case R_X86_64_PLT32:
>           /*
>            * NONE can be ignored and PC relative relocations don't
>            * need to be adjusted.
> --- a/arch/x86/kernel/module.c    2020-01-24 18:46:54.922670590 -0500
> +++ b/arch/x86/kernel/module.c    2020-01-24 18:47:46.714112016 -0500
> @@ -180,6 +180,7 @@ int apply_relocate_add(Elf64_Shdr *sechd
>                   goto overflow;
>               break;
>           case R_X86_64_PC32:
> +        case R_X86_64_PLT32:
>               val -= (u64)loc;
>               *(u32 *)loc = val;
>   #if 0
> 
-- 
Ben Hutchings
The program is absolutely right; therefore, the computer must be wrong.

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