From: "Masami Hiramatsu (Google)" mhiramat@kernel.org
[ 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@dev...
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 --- kernel/trace/trace_probe.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+)
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index 16a5e368e7b77..578919962e5df 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -770,6 +770,10 @@ 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; @@ -793,6 +797,20 @@ 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) { @@ -826,6 +844,16 @@ 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: