[PATCH v2 0/7] tracing/probes: Support function parameter access from return probe

From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>, Jiri Olsa <jolsa@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
	mhiramat@kernel.org, linux-doc@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Subject: [PATCH v2 0/7] tracing/probes: Support function parameter access from return probe
Date: Mon, 26 Feb 2024 12:57:53 +0900	[thread overview]
Message-ID: <170891987362.609861.6767830614537418260.stgit@devnote2> (raw)

Hi,

Here is version 2 series of patches to support accessing function entry data
from function *return* probes (including kretprobe and fprobe-exit event).

In this version, I added another cleanup [4/7], updated README[5/7], added
testcases[6/7] and updated document[7/7].

This allows us to access the results of some functions, which returns the
error code and its results are passed via function parameter, such as an
structure-initialization function.

For example, vfs_open() will link the file structure to the inode and update
mode. Thus we can trace that changes.

 # echo 'f vfs_open mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
 # echo 'f vfs_open%return mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events 
 # echo 1 > events/fprobes/enable 
 # cat trace
              sh-131     [006] ...1.  1945.714346: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x2 inode=0x0
              sh-131     [006] ...1.  1945.714358: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4d801e inode=0xffff888008470168
             cat-143     [007] ...1.  1945.717949: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
             cat-143     [007] ...1.  1945.717956: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4a801d inode=0xffff888005f78d28
             cat-143     [007] ...1.  1945.720616: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
             cat-143     [007] ...1.  1945.728263: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0xa800d inode=0xffff888004ada8d8

So as you can see those fields are initialized at exit.

This series is based on v6.8-rc5 kernel or you can checkout from

https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/entry-data

Thank you,

---

Masami Hiramatsu (Google) (7):
      tracing/fprobe-event: cleanup: Fix a wrong comment in fprobe event
      tracing/probes: Cleanup probe argument parser
      tracing/probes: cleanup: Set trace_probe::nr_args at trace_probe_init
      tracing: Remove redundant #else block for BTF args from README
      tracing/probes: Support $argN in return probe (kprobe and fprobe)
      selftests/ftrace: Add test cases for entry args at function exit
      Documentation: tracing: Add entry argument access at function exit

 Documentation/trace/fprobetrace.rst                |    7 
 Documentation/trace/kprobetrace.rst                |    7 
 kernel/trace/trace.c                               |    5 
 kernel/trace/trace_eprobe.c                        |    8 
 kernel/trace/trace_fprobe.c                        |   59 ++-
 kernel/trace/trace_kprobe.c                        |   58 ++-
 kernel/trace/trace_probe.c                         |  417 ++++++++++++++------
 kernel/trace/trace_probe.h                         |   30 +
 kernel/trace/trace_probe_tmpl.h                    |   10 
 kernel/trace/trace_uprobe.c                        |   14 -
 .../ftrace/test.d/dynevent/fprobe_entry_arg.tc     |   18 +
 .../ftrace/test.d/kprobe/kretprobe_entry_arg.tc    |   18 +
 12 files changed, 483 insertions(+), 168 deletions(-)
 create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/fprobe_entry_arg.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_entry_arg.tc

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>