linux-kernel - Re: [RFC PATCH 2/3] LoongArch: Add larch_insn_gen

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Date:   Fri, 7 Apr 2023 17:51:57 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Youling Tang <tangyouling@...ngson.cn>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...nel.org>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [RFC PATCH 2/3] LoongArch: Add larch_insn_gen_break() to generate
 break insn

On 2023/4/7 10:30, Youling Tang wrote:
> /* snip */
> 
>> diff --git a/arch/loongarch/kernel/kprobes.c 
>> b/arch/loongarch/kernel/kprobes.c
>> index 08c78d2..a5c3712 100644
>> --- a/arch/loongarch/kernel/kprobes.c
>> +++ b/arch/loongarch/kernel/kprobes.c
>> @@ -4,19 +4,8 @@
>>  #include <linux/preempt.h>
>>  #include <asm/break.h>
>>
>> -static const union loongarch_instruction breakpoint_insn = {
>> -    .reg0i15_format = {
>> -        .opcode = break_op,
>> -        .immediate = BRK_KPROBE_BP,
>> -    }
>> -};
>> -
>> -static const union loongarch_instruction singlestep_insn = {
>> -    .reg0i15_format = {
>> -        .opcode = break_op,
>> -        .immediate = BRK_KPROBE_SSTEPBP,
>> -    }
>> -};
>> +#define breakpoint_insn larch_insn_gen_break(BRK_KPROBE_BP)
>> +#define singlestep_insn larch_insn_gen_break(BRK_KPROBE_SSTEPBP)
> 
> IMO, Defined as KPROBE_BP_INSN, KPROBE_SSTEPBP_INSN may be better.

Are you suggesting to hardcode the instruction words for those two BREAK 
flavors? I don't think it's better because even more structured info is 
lost, and the compiler would generate the same code (if not, it's the 
compiler that's to be fixed).

Actually, I don't know why this commit was necessary in the first place. 
For the very least, it consisted of two logical changes (pass around 
instruction words instead of unions; and change the BREAK insns to make 
them words) that should get split; but again, the generated code should 
be identical anyway, so it seems a lot of churn for no benefit and 
reduced readability.

-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/