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

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