linux-kernel - Re: [PATCHv8 bpf-next 3/9] uprobe: Add uretprobe syscall to speed up return probe

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Date: Fri, 14 Jun 2024 21:26:59 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-man@...r.kernel.org, x86@...nel.org, bpf@...r.kernel.org,
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Borislav Petkov (AMD)" <bp@...en8.de>,
	Ingo Molnar <mingo@...hat.com>, Andy Lutomirski <luto@...nel.org>,
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
	Deepak Gupta <debug@...osinc.com>,
	Huacai Chen <chenhuacai@...nel.org>, loongarch@...ts.linux.dev
Subject: Re: [PATCHv8 bpf-next 3/9] uprobe: Add uretprobe syscall to speed up
 return probe

On Fri, Jun 14, 2024 at 10:48:22AM -0700, Nathan Chancellor wrote:
> Hi Jiri,
> 
> On Tue, Jun 11, 2024 at 01:21:52PM +0200, Jiri Olsa wrote:
> > Adding uretprobe syscall instead of trap to speed up return probe.
> ...
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 2c83ba776fc7..2816e65729ac 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -1474,11 +1474,20 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
> >  	return ret;
> >  }
> >  
> > +void * __weak arch_uprobe_trampoline(unsigned long *psize)
> > +{
> > +	static uprobe_opcode_t insn = UPROBE_SWBP_INSN;
> 
> This change as commit ff474a78cef5 ("uprobe: Add uretprobe syscall to
> speed up return probe") in -next causes the following build error for
> ARCH=loongarch allmodconfig:
> 
>   In file included from include/linux/uprobes.h:49,
>                    from include/linux/mm_types.h:16,
>                    from include/linux/mmzone.h:22,
>                    from include/linux/gfp.h:7,
>                    from include/linux/xarray.h:16,
>                    from include/linux/list_lru.h:14,
>                    from include/linux/fs.h:13,
>                    from include/linux/highmem.h:5,
>                    from kernel/events/uprobes.c:13:
>   kernel/events/uprobes.c: In function 'arch_uprobe_trampoline':
>   arch/loongarch/include/asm/uprobes.h:12:33: error: initializer element is not constant
>      12 | #define UPROBE_SWBP_INSN        larch_insn_gen_break(BRK_UPROBE_BP)
>         |                                 ^~~~~~~~~~~~~~~~~~~~
>   kernel/events/uprobes.c:1479:39: note: in expansion of macro 'UPROBE_SWBP_INSN'
>    1479 |         static uprobe_opcode_t insn = UPROBE_SWBP_INSN;

reproduced, could you please try the change below

thanks,
jirka


---
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 2816e65729ac..6986bd993702 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1476,8 +1476,9 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
 
 void * __weak arch_uprobe_trampoline(unsigned long *psize)
 {
-	static uprobe_opcode_t insn = UPROBE_SWBP_INSN;
+	static uprobe_opcode_t insn;
 
+	insn = insn ?: UPROBE_SWBP_INSN;
 	*psize = UPROBE_SWBP_INSN_SIZE;
 	return &insn;
 }