linux-kernel - Re: [PATCH] LoongArch: Correct the definition of is_branch

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Message-ID: <e65ce2d5-a154-6912-ab01-b0dc158acaaa@loongson.cn>
Date:   Fri, 16 Dec 2022 14:11:03 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Jinyang He <hejinyang@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Correct the definition of is_branch_ins()



On 12/16/2022 11:18 AM, Jinyang He wrote:
> Hi, Tiezhu,
>
>
> On 2022-12-14 16:30, Tiezhu Yang wrote:
>> The current definition of is_branch_ins() is not correct,
>
> But the branch instruction opcode only use the high 6 bits,

Yes, I noticed that, the logic result of current code is right,
but it seems a little strange (only consider reg1i21_format)
at the first glance, the initial aim of this patch is to make
it theoretically correct, maybe it is not the best change.

I think we can neglect the instruction formats and check the
high 6 bits instead, what do you think of the following change?

diff --git a/arch/loongarch/include/asm/inst.h 
b/arch/loongarch/include/asm/inst.h
index c00e151..fd31752 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -329,8 +329,8 @@ static inline bool is_pc_ins(union 
loongarch_instruction *ip)

  static inline bool is_branch_ins(union loongarch_instruction *ip)
  {
-       return ip->reg1i21_format.opcode >= beqz_op &&
-               ip->reg1i21_format.opcode <= bgeu_op;
+       return ((ip->word >> 26) & 0x3f) >= beqz_op &&
+               ((ip->word >> 26) & 0x3f) <= bgeu_op;
  }

Thanks,
Tiezhu