Hi,
Here is a series of patches to support accessing function entry data from
function *return* probes (including kretprobe and fprobe-exit event).
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.
TODO:
- update README file
- add/update ftracetest
- update documents
Thank you,
---
Masami Hiramatsu (Google) (5):
tracing/probes: Fix to search structure fields correctly
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/probes: Support $argN in return probe (kprobe and fprobe)
kernel/trace/trace_btf.c | 4
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 +
8 files changed, 433 insertions(+), 167 deletions(-)
--
Masami Hiramatsu (Google) <mhira...@kernel.org>
