Re: [PATCH 1/2] riscv: ftrace: Fix the comments about the number of ftrace instruction

[Guo Ren]

On Tue, Apr 26, 2022 at 9:59 AM Li Huafei <lihuafei1@xxxxxxxxxx> wrote:
>
> When DYNAMIC_FTRACE is enabled, we put four instructions in front of the
> function for ftrace use, not five.
>
> Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
> ---
>  arch/riscv/kernel/ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 4716f4cdc038..63f457650fa4 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -73,7 +73,7 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
>  }
>
>  /*
> - * Put 5 instructions with 16 bytes at the front of function within
> + * Put 4 instructions with 16 bytes at the front of function within
Yeah, 5 instructions are for mcount, -fpatchable-function-entry=8
cause 8 16bit instructions.

Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")

I recommend just delete "4 instructions with"
- * Put 5 instructions with 16 bytes at the front of function within
- * patchable function entry nops' area.
+ * Put 16 bytes at the front of the function within the patchable
+ * function entry nops' area.

>   * patchable function entry nops' area.
>   *
>   * 0: REG_S  ra, -SZREG(sp)
> --
> 2.17.1
>


-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/