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 16:52:55 +0800
From:   Li Huafei <lihuafei1@...wei.com>
To:     Guo Ren <guoren@...nel.org>
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 2022/4/26 14:22, Guo Ren wrote:
> 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.
I misunderstood, thanks for the clarification.
>
> Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
There is no functional fix here, do we need to add the fix tag?
>
> 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.

I agree and will use this modification for the next version, thanks!


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