[PATCH v3 1/7] scripts/sorttable: Make the arm64 before_func offset configurable

[Steven Rostedt]

On Thu, 29 Oct 2026 16:53:58 +0000
"Jose Fernandez (Anthropic)" <jose.fernandez at linux.dev> wrote:

> sorttable hardcodes before_func to 8 bytes on arm64 (two prefix NOPs).
> Make it configurable from CONFIG_ARM64_FUNCTION_PREFIX_NOPS instead.
> kCFI kernels with CALL_OPS need three NOPs. The symbol does not exist
> yet, so no functional change.
> 
> Reviewed-by: Ben Cressey <ben at cressey.dev>
> Reviewed-by: Florent Revest (Anthropic) <florent.revest at linux.dev>
> Acked-by: Alexei Starovoitov <ast at kernel.org>
> Assisted-by: LLM
> Signed-off-by: Jose Fernandez (Anthropic) <jose.fernandez at linux.dev>

Reviewed-by: Steven Rostedt <rostedt at goodmis.org>

-- Steve

> ---
>  scripts/Makefile    | 4 ++++
>  scripts/sorttable.c | 7 ++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/Makefile b/scripts/Makefile
> index d7fbb7ca098b..7ef1c84cf79d 100644
> --- a/scripts/Makefile
> +++ b/scripts/Makefile
> @@ -54,6 +54,10 @@ endif
>  
>  ifdef CONFIG_BUILDTIME_MCOUNT_SORT
>  HOSTCFLAGS_sorttable.o += -DMCOUNT_SORT_ENABLED
> +# 0 or unset (no prefix NOPs) leaves sorttable's built-in default in place.
> +ifneq ($(filter-out 0,$(CONFIG_ARM64_FUNCTION_PREFIX_NOPS)),)
> +HOSTCFLAGS_sorttable.o += -DFUNCTION_PREFIX_BYTES=$(shell expr 4 \* $(CONFIG_ARM64_FUNCTION_PREFIX_NOPS))
> +endif
>  endif
>  
>  hostprogs += gen_init_cpio
> diff --git a/scripts/sorttable.c b/scripts/sorttable.c
> index 88e49a5c4251..2e951f2f60e8 100644
> --- a/scripts/sorttable.c
> +++ b/scripts/sorttable.c
> @@ -281,6 +281,11 @@ static int add_field(uint64_t addr, uint64_t size)
>  /* Used for when mcount/fentry is before the function entry */
>  static int before_func;
>  
> +/* How far before the function entry a patchable entry may be recorded */
> +#ifndef FUNCTION_PREFIX_BYTES
> +#define FUNCTION_PREFIX_BYTES	8
> +#endif
> +
>  /* Only return match if the address lies inside the function size */
>  static int cmp_func_addr(const void *K, const void *A)
>  {
> @@ -912,7 +917,7 @@ static int do_file(char const *const fname, void *addr)
>  		/* fallthrough */
>  	case EM_RISCV:
>  		/* arm64 and RISC-V place patchable entries before the function. */
> -		before_func = 8;
> +		before_func = FUNCTION_PREFIX_BYTES;
>  #else
>  	case EM_AARCH64:
>  	case EM_RISCV:
>