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Date: Tue, 23 Apr 2024 00:07:29 +0900
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, Oleg Nesterov <oleg@redhat.com>,
 Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann
 <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>,
 linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
 linux-api@vger.kernel.org, x86@kernel.org, bpf@vger.kernel.org, Song Liu
 <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>, John Fastabend
 <john.fastabend@gmail.com>, Peter Zijlstra <peterz@infradead.org>, Thomas
 Gleixner <tglx@linutronix.de>, "Borislav Petkov (AMD)" <bp@alien8.de>, Ingo
 Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 7/7] man2: Add uretprobe syscall page
Message-Id: <20240423000729.f1d58443100c3994afca0a7f@kernel.org>
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On Sun, 21 Apr 2024 21:42:06 +0200
Jiri Olsa <jolsa@kernel.org> wrote:

> Adding man page for new uretprobe syscall.
> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.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@kernel.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?

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."

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@kernel.org>