linux-kernel - Re: [PATCH] uprobe: Do not use UPROBE_SWBP

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Date: Thu, 20 Jun 2024 14:30:03 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: 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
Subject: Re: [PATCH] uprobe: Do not use UPROBE_SWBP_INSN as static initializer

On Thu, Jun 20, 2024 at 12:40 PM Oleg Nesterov <oleg@...hat.com> wrote:
>
> On 06/20, Andrii Nakryiko wrote:
> >
> > Can we instead ask loongarch folks to rewrite it to be a constant?
> > Having this as a function call is both an inconvenience and potential
> > performance problem (a minor one, but still). I would imagine it's not
> > hard to hard-code an instruction as a constant here.
>
> I was going to ask the same question when I saw the bug report ;)
> The same for other users of larch_insn_gen_break().
>
> But I can't understand what does it do, it calls emit_break() and
> git grep -w emit_break finds nothing.
>

It's DEF_EMIT_REG0I15_FORMAT(break, break_op) in
arch/loongarch/include/asm/inst.h

A bunch of macro magic, but in the end it produces some constant
value, of course.

> Oleg.
>