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@xxxxxxxxxx>
