linux-kernel - Re: [PATCH 7/7] man2: Add uretprobe syscall page

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Date: Mon, 22 Apr 2024 22:15:14 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.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,
	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>
Subject: Re: [PATCH 7/7] man2: Add uretprobe syscall page

On Tue, Apr 23, 2024 at 12:07:29AM +0900, Masami Hiramatsu wrote:
> On Sun, 21 Apr 2024 21:42:06 +0200
> Jiri Olsa <jolsa@...nel.org> wrote:
> 
> > Adding man page for new uretprobe syscall.
> > 
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  man2/uretprobe.2 | 40 ++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 40 insertions(+)
> >  create mode 100644 man2/uretprobe.2
> > 
> > diff --git a/man2/uretprobe.2 b/man2/uretprobe.2
> > new file mode 100644
> > index 000000000000..c0343a88bb57
> > --- /dev/null
> > +++ b/man2/uretprobe.2
> > @@ -0,0 +1,40 @@
> > +.\" Copyright (C) 2024, Jiri Olsa <jolsa@...nel.org>
> > +.\"
> > +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> > +.\"
> > +.TH uretprobe 2 (date) "Linux man-pages (unreleased)"
> > +.SH NAME
> > +uretprobe \- execute pending return uprobes
> > +.SH SYNOPSIS
> > +.nf
> > +.B int uretprobe(void)
> > +.fi
> > +.SH DESCRIPTION
> > +On x86_64 architecture the kernel is using uretprobe syscall to trigger
> > +uprobe return probe consumers instead of using standard breakpoint instruction.
> > +The reason is that it's much faster to do syscall than breakpoint trap
> > +on x86_64 architecture.
> 
> Do we specify the supported architecture as this? Currently it is supported
> only on x86-64, but it could be extended later, right?

yes, that's the idea, but I can't really speak other than x86 ;-)
so not sure abour other archs details

> 
> This should be just noted as NOTES. Something like "This syscall is initially
> introduced on x86-64 because a syscall is faster than a breakpoint trap on it.
> But this will be extended to the architectures whose syscall is faster than
> breakpoint trap."

's/will be extended/might be will be extended/' seems better to me,
other than that it looks ok

thanks,
jirka


> 
> Thank you,
> 
> > +
> > +The uretprobe syscall is not supposed to be called directly by user, it's allowed
> > +to be invoked only through user space trampoline provided by kernel.
> > +When called from outside of this trampoline, the calling process will receive
> > +.BR SIGILL .
> > +
> > +.SH RETURN VALUE
> > +.BR uretprobe()
> > +return value is specific for given architecture.
> > +
> > +.SH VERSIONS
> > +This syscall is not specified in POSIX,
> > +and details of its behavior vary across systems.
> > +.SH STANDARDS
> > +None.
> > +.SH NOTES
> > +.BR uretprobe()
> > +exists only to allow the invocation of return uprobe consumers.
> > +It should
> > +.B never
> > +be called directly.
> > +Details of the arguments (if any) passed to
> > +.BR uretprobe ()
> > +and the return value are specific for given architecture.
> > -- 
> > 2.44.0
> > 
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>