Re: [PATCH v2 08/59] x86/build: Ensure proper function alignment

[Linus Torvalds]

On Fri, Sep 2, 2022 at 6:55 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> --- a/arch/x86/include/asm/linkage.h
> +++ b/arch/x86/include/asm/linkage.h
> @@ -14,9 +14,10 @@
>
>  #ifdef __ASSEMBLY__
>
> -#if defined(CONFIG_X86_64) || defined(CONFIG_X86_ALIGNMENT_16)
> -#define __ALIGN                .p2align 4, 0x90
> -#define __ALIGN_STR    __stringify(__ALIGN)
> +#if CONFIG_FUNCTION_ALIGNMENT == 16
> +#define __ALIGN                        .p2align 4, 0x90
> +#define __ALIGN_STR            __stringify(__ALIGN)
> +#define FUNCTION_ALIGNMENT     16
>  #endif

Ugh.

Why is this conditional on that alignment being 16?

Is it purely because the CONFIG variable was mis-designed, and is the
number of bytes, instead of being the shift? If so, just fix that, and
then do an unconditional

  #define __ALIGN                        .p2align
CONFIG_FUNCTION_ALIGNMENT_SHIFT, 0x90
  #define __ALIGN_STR            __stringify(__ALIGN)

(leave the asm-generic one conditional, since then the condition makes
sense - it's arch-specific).

           Linus