linux-kernel - Re: [PATCH v7 1/4] LoongArch: Simulate branch and PC instructions

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Message-ID: <a3ed9194-ff36-19ff-8cdd-2cfba12c17a9@loongson.cn>
Date:   Wed, 7 Dec 2022 17:13:54 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>
Cc:     WANG Xuerui <kernel@...0n.name>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/4] LoongArch: Simulate branch and PC instructions

On 12/07/2022 11:06 AM, Huacai Chen wrote:
> Hi, Tiezhu,
>
> On Fri, Dec 2, 2022 at 9:08 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>>
>> According to LoongArch Reference Manual, simulate branch and
>> PC instructions, this is preparation for later patch.
>>

...

>> +static inline unsigned long sign_extended(unsigned long val, unsigned int idx)
>> +{
>> +       if (val & (1UL << idx))
>> +               return ~((1UL << (idx + 1)) - 1) | val;
>> +       else
>> +               return ((1UL << (idx + 1)) - 1) & val;
>> +}
> You can use existing __SIGNEX and its friends rather than reinvent them.

Thanks for your reminder.

In my opinion, this static inline function sign_extended()
is much more clear and readable than the macro __SIGNEX()
defined in alternative.c, the helper function bs_dest_*()
seems redundant too, use "pc + sign_extended()" is a more
straightforward way to simulate instruction according to
the ISA Manual, so here I prefer to keep it as is.

Additionally, we can use sign_extended() instead of __SIGNEX()
in alternative.c, the __SIGNEX() related code can be removed
in a seperate patch in some day.

Thanks,
Tiezhu