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

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Message-ID: <ZnV9hvOP5388YJtw@krava>
Date: Fri, 21 Jun 2024 15:17:58 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Oleg Nesterov <oleg@...hat.com>, Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>,
	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,
	loongarch@...ts.linux.dev
Subject: Re: [PATCH] uprobe: Do not use UPROBE_SWBP_INSN as static initializer

On Fri, Jun 21, 2024 at 02:01:50PM +0200, Oleg Nesterov wrote:
> On 06/20, Andrii Nakryiko wrote:
> >
> > On Thu, Jun 20, 2024 at 12:40 PM Oleg Nesterov <oleg@...hat.com> wrote:
> > >
> > > 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.
> 
> I see, thanks!
> 
> Then perhaps something like below?

lgtm, added loong arch list/folks

for context:
  https://lore.kernel.org/bpf/20240614174822.GA1185149@thelio-3990X/

thanks,
jirka

> 
> Oleg.
> 
> 
> --- x/arch/loongarch/include/asm/uprobes.h
> +++ x/arch/loongarch/include/asm/uprobes.h
> @@ -9,7 +9,7 @@ typedef u32 uprobe_opcode_t;
>  #define MAX_UINSN_BYTES		8
>  #define UPROBE_XOL_SLOT_BYTES	MAX_UINSN_BYTES
>  
> -#define UPROBE_SWBP_INSN	larch_insn_gen_break(BRK_UPROBE_BP)
> +#define UPROBE_SWBP_INSN	(uprobe_opcode_t)(BRK_UPROBE_BP | (break_op << 15))
>  #define UPROBE_SWBP_INSN_SIZE	LOONGARCH_INSN_SIZE
>  
>  #define UPROBE_XOLBP_INSN	larch_insn_gen_break(BRK_UPROBE_XOLBP)
> --- x/arch/loongarch/kernel/uprobes.c
> +++ x/arch/loongarch/kernel/uprobes.c
> @@ -7,6 +7,13 @@
>  
>  #define UPROBE_TRAP_NR	UINT_MAX
>  
> +static __init int __ck_insn(void)
> +{
> +	BUG_ON(UPROBE_SWBP_INSN != larch_insn_gen_break(BRK_UPROBE_BP));
> +	return 0;
> +}
> +late_initcall(__ck_insn);
> +
>  int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
>  			     struct mm_struct *mm, unsigned long addr)
>  {
>