[PATCH v3 0/8] tracing/probes: Support function parameter access from return probe

Masami Hiramatsu (Google)
2024-03-04T03:40:01Z

Hi,

Here is version 3 series of patches to support accessing function entry data
from function *return* probes (including kretprobe and fprobe-exit event).
The previous version is here;

https://lore.kernel.org/all/170891987362.609861.6767830614537418260.stgit@devnote2/

In this version, [1/8] is a bugfix patch (but note that this is already pushed to
probes-fixes-v6.8-rc5, just for reference), updated [4/8] changelog and build error,
fixes selftests error [6/8], update document[8/8] and added Steve's reviewed-by.

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) (8):
fprobe: Fix to allocate entry_data_size buffer with rethook instances
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 | 31 +
Documentation/trace/kprobetrace.rst | 9
kernel/trace/fprobe.c | 14 -
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/dynevent/fprobe_syntax_errors.tc | 4
.../ftrace/test.d/kprobe/kprobe_syntax_errors.tc | 2
.../ftrace/test.d/kprobe/kretprobe_entry_arg.tc | 18 +
15 files changed, 521 insertions(+), 176 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>