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| author | Masami Hiramatsu (Google) <mhiramat@kernel.org> | 2023-11-10 19:59:03 +0900 |
|---|---|---|
| committer | Masami Hiramatsu (Google) <mhiramat@kernel.org> | 2023-11-10 19:59:03 +0900 |
| commit | b2a866975f6cd5859c746f1da39c8f5736c8def2 (patch) | |
| tree | 7e5874462fded7cd95f8e259cde12e4c68d9167f | |
| parent | 89cdf9d556016a54ff6ddd62324aa5ec790c05cc (diff) | |
| download | lwn-b2a866975f6cd5859c746f1da39c8f5736c8def2.tar.gz lwn-b2a866975f6cd5859c746f1da39c8f5736c8def2.zip | |
Documentation: tracing: Add a note about argument and retval access
Add a note about the argument and return value accecss will be best
effort. Depending on the type, it will be passed via stack or a
pair of the registers, but $argN and $retval only support the
single register access.
Link: https://lore.kernel.org/all/169556269377.146934.14829235476649685954.stgit@devnote2/
Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
| -rw-r--r-- | Documentation/trace/fprobetrace.rst | 8 | ||||
| -rw-r--r-- | Documentation/trace/kprobetrace.rst | 8 |
2 files changed, 12 insertions, 4 deletions
diff --git a/Documentation/trace/fprobetrace.rst b/Documentation/trace/fprobetrace.rst index 8e9bebcf0a2e..e35e6b18df40 100644 --- a/Documentation/trace/fprobetrace.rst +++ b/Documentation/trace/fprobetrace.rst @@ -59,8 +59,12 @@ Synopsis of fprobe-events and bitfield are supported. (\*1) This is available only when BTF is enabled. - (\*2) only for the probe on function entry (offs == 0). - (\*3) only for return probe. + (\*2) only for the probe on function entry (offs == 0). Note, this argument access + is best effort, because depending on the argument type, it may be passed on + the stack. But this only support the arguments via registers. + (\*3) only for return probe. Note that this is also best effort. Depending on the + return value type, it might be passed via a pair of registers. But this only + accesses one register. (\*4) this is useful for fetching a field of data structures. (\*5) "u" means user-space dereference. diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst index 8a2dfee38145..bf9cecb69fc9 100644 --- a/Documentation/trace/kprobetrace.rst +++ b/Documentation/trace/kprobetrace.rst @@ -61,8 +61,12 @@ Synopsis of kprobe_events (x8/x16/x32/x64), "char", "string", "ustring", "symbol", "symstr" and bitfield are supported. - (\*1) only for the probe on function entry (offs == 0). - (\*2) only for return probe. + (\*1) only for the probe on function entry (offs == 0). Note, this argument access + is best effort, because depending on the argument type, it may be passed on + the stack. But this only support the arguments via registers. + (\*2) only for return probe. Note that this is also best effort. Depending on the + return value type, it might be passed via a pair of registers. But this only + accesses one register. (\*3) this is useful for fetching a field of data structures. (\*4) "u" means user-space dereference. See :ref:`user_mem_access`. |