Re: [RFC PATCH 2/3] LoongArch: Add larch_insn_gen_break() to generate break insn

[WANG Xuerui]

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

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