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

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Date:   Tue, 26 Apr 2022 14:22:18 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Li Huafei <lihuafei1@...wei.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        David Miller <davem@...emloft.net>, jszhang@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, liaochang1@...wei.com,
        Patrick Stählin <me@...ki.ch>,
        Pekka Enberg <penberg@...nel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] riscv: ftrace: Fix the comments about the number of
 ftrace instruction

On Tue, Apr 26, 2022 at 9:59 AM Li Huafei <lihuafei1@...wei.com> 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@...wei.com>
> ---
>  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/