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tracing: probe-events: Add comments about entry data storing code

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[ Upstream commit bb9c6020f4c3a07a90dc36826cb5fbe83f09efd5 ]

Add comments about entry data storing code to __store_entry_arg() and
traceprobe_get_entry_data_size(). These are a bit complicated because of
building the entry data storing code and scanning it.

This just add comments, no behavior change.

Link: https://lore.kernel.org/all/174061715004.501424.333819546601401102.stgit@devnote2/

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Closes: https://lore.kernel.org/all/20250226102223.586d7119@gandalf.local.home/
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Masami Hiramatsu (Google)
2025-03-27 21:19:54 +09:00
committed by Greg Kroah-Hartman
parent fda15c5b96
commit 14345d5d7d
1 changed files with 28 additions and 0 deletions
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28
kernel/trace/trace_probe.c
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@@ -769,6 +769,10 @@ static int check_prepare_btf_string_fetch(char *typename,
#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
/*
* Add the entry code to store the 'argnum'th parameter and return the offset
* in the entry data buffer where the data will be stored.
*/
static int __store_entry_arg(struct trace_probe *tp, int argnum)
{
struct probe_entry_arg *earg = tp->entry_arg;
@@ -792,6 +796,20 @@ static int __store_entry_arg(struct trace_probe *tp, int argnum)
tp->entry_arg = earg;
}
/*
* The entry code array is repeating the pair of
* [FETCH_OP_ARG(argnum)][FETCH_OP_ST_EDATA(offset of entry data buffer)]
* and the rest of entries are filled with [FETCH_OP_END].
*
* To reduce the redundant function parameter fetching, we scan the entry
* code array to find the FETCH_OP_ARG which already fetches the 'argnum'
* parameter. If it doesn't match, update 'offset' to find the last
* offset.
* If we find the FETCH_OP_END without matching FETCH_OP_ARG entry, we
* will save the entry with FETCH_OP_ARG and FETCH_OP_ST_EDATA, and
* return data offset so that caller can find the data offset in the entry
* data buffer.
*/
offset = 0;
for (i = 0; i < earg->size - 1; i++) {
switch (earg->code[i].op) {
@@ -825,6 +843,16 @@ int traceprobe_get_entry_data_size(struct trace_probe *tp)
if (!earg)
return 0;
/*
* earg->code[] array has an operation sequence which is run in
* the entry handler.
* The sequence stopped by FETCH_OP_END and each data stored in
* the entry data buffer by FETCH_OP_ST_EDATA. The FETCH_OP_ST_EDATA
* stores the data at the data buffer + its offset, and all data are
* "unsigned long" size. The offset must be increased when a data is
* stored. Thus we need to find the last FETCH_OP_ST_EDATA in the
* code array.
*/
for (i = 0; i < earg->size; i++) {
switch (earg->code[i].op) {
case FETCH_OP_END: