[RFC PATCH riscv/for-next 1/4] riscv: align ftrace to 4 Byte boundary and increase ftrace prologue size

[Palmer Dabbelt]

On Sun, 29 May 2022 07:33:12 PDT (-0700), andy.chiu at sifive.com wrote:
> We are introducing a new ftrace mechanism in order to phase out
> stop_machine() and enable kernel preemption. The new mechanism requires
> ftrace patchable function entries to be 24 bytes and aligned to 4 Byte
> boundaries.
>
> Before applying this patch, the size of the kernel code, with 43432 of
> ftrace entries, was at 12.31 MB. Under the same configuration, the size
> has increased to 12.68 MB after applying this patch set.
>
> Signed-off-by: Andy Chiu <andy.chiu at sifive.com>
> Reviewed-by: Greentime Hu <greentime.hu at sifive.com>
> Reviewed-by: Zong Li <zong.li at sifive.com>
> ---
>  arch/riscv/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 1f19bdac6767..cb6cfdffc49c 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -11,7 +11,7 @@ LDFLAGS_vmlinux :=
>  ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>  	LDFLAGS_vmlinux := --no-relax
>  	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> -	CC_FLAGS_FTRACE := -fpatchable-function-entry=8
> +	CC_FLAGS_FTRACE := -fpatchable-function-entry=12  -falign-functions=4
>  endif
>
>  ifeq ($(CONFIG_CMODEL_MEDLOW),y)

Reviewed-by: Palmer Dabbelt <palmer at rivosinc.com>