On Tue, Apr 23, 2024 at 12:07:29AM +0900, Masami Hiramatsu wrote:

On Sun, 21 Apr 2024 21:42:06 +0200
Jiri Olsa [off-list ref] wrote:

quoted

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?

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,

quoted

+
+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) [off-list ref]