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

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Message-ID: <20240621120149.GB12521@redhat.com>
Date: Fri, 21 Jun 2024 14:01:50 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.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 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?

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)
 {