On Wed, Mar 09, 2022 at 03:57:16PM +0000, Marc Zyngier wrote:
> Compiling the arm64 kernel with the BHB workarounds and Clang+LTO
> results in a bunch of:
> 
> <instantiation>:4:2: error: invalid fixup for movz/movk instruction
>  mov w0, #ARM_SMCCC_ARCH_WORKAROUND_3
> 
> when compiling arch/arm64/kernel/entry.S, and makes no sense at all.
> 
> As it turns out, moving a single include line around makes the
> problem disappear. Why, you'd ask? Well, I don't have the faintest
> idea, and I'm running out of patience. So make of that what you want.
> 
> Cc: James Morse <james.morse@arm.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  include/linux/arm-smccc.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index 220c8c60e021..0a341dd9ff61 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -5,7 +5,6 @@
>  #ifndef __LINUX_ARM_SMCCC_H
>  #define __LINUX_ARM_SMCCC_H
>  
> -#include <linux/init.h>
>  #include <uapi/linux/const.h>
>  
>  /*
> @@ -193,6 +192,7 @@
>  
>  #ifndef __ASSEMBLY__
>  
> +#include <linux/init.h>
>  #include <linux/linkage.h>
>  #include <linux/types.h>
>  
> -- 
> 2.34.1

I am still looking at this but I wanted to post a preliminary finding.
It seems the source of the error is that ARM_SMCCC_ARCH_WORKAROUND_3 is
not getting expanded by the preprocessor. If you preprocess
arch/arm64/kernel/entry.S without LTO then with LTO, it reveals the
attached diff, which shows just "#ARM_SMCCC_ARCH_WORKAROUND_3", rather
than "# (((1) << 31) | ((0) << 30) | (((0) & 0x3F) << 24) | ((0x3fff) & 0xFFFF))".

$ make -skj"$(nproc)" ARCH=arm64 LLVM=1 mrproper defconfig arch/arm64/kernel/entry.s

I'll see if I can figure out what is going wrong in the include chain.

Cheers,
Nathan