linux-kernel - Re: [PATCH] LoongArch: uprobes: make UPROBE_SWBP_INSN/UPROBE_XOLBP

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Date: Thu, 27 Jun 2024 19:38:06 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, Jiri Olsa <jolsa@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev
Subject: Re: [PATCH] LoongArch: uprobes: make
 UPROBE_SWBP_INSN/UPROBE_XOLBP_INSN constant

On 06/27, Andrii Nakryiko wrote:
>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>

Thanks!

> > --- a/arch/loongarch/kernel/uprobes.c
> > +++ b/arch/loongarch/kernel/uprobes.c
> > @@ -7,6 +7,14 @@
> >
> >  #define UPROBE_TRAP_NR UINT_MAX
> >
> > +static __init int check_emit_break(void)
> > +{
> > +       BUG_ON(UPROBE_SWBP_INSN  != larch_insn_gen_break(BRK_UPROBE_BP));
> > +       BUG_ON(UPROBE_XOLBP_INSN != larch_insn_gen_break(BRK_UPROBE_XOLBP));
> > +       return 0;
> > +}
> > +arch_initcall(check_emit_break);
> > +
>
> I wouldn't even bother with this, but whatever.

Agreed, this looks a bit ugly. I did this only because I can not test
this (hopefully trivial) patch and the maintainers didn't reply.

If LoongArch boots at least once with this change, this run-time check
can be removed.

And just in case... I didn't dare to make a more "generic" change, but
perhaps KPROBE_BP_INSN and KPROBE_SSTEPBP_INSN should be redefined the
same way for micro-optimization. In this case __emit_break() should be
probably moved into arch/loongarch/include/asm/inst.h.

Oleg.