Merge tag 'probes-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull probes updates from Masami Hiramatsu:

 - probe-events: Add comments about entry data storing code to clarify
   where and how the entry data is stored for function return events.

 - probe-events: Log error for exceeding the number of arguments to help
   user to identify error reason via tracefs/error_log file.

 - Improve the ftracetest selftests:
    - Expand the tprobe event test to check if it can correctly find the
      wrong format tracepoint name.
    - Add new syntax error test to check whether error_log correctly
      indicates a wrong character in the tracepoint name.
    - Add a new dynamic events argument limitation test case which
      checks max number of probe arguments.

* tag 'probes-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  tracing: probe-events: Add comments about entry data storing code
  selftests/ftrace: Add dynamic events argument limitation test case
  selftests/ftrace: Add new syntax error test
  selftests/ftrace: Expand the tprobe event test to check wrong format
  tracing: probe-events: Log error for exceeding the number of arguments

6 files changed, 46 insertions, 4 deletions

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index c1cc2fe54887..c08355c3ef32 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -913,6 +913,8 @@ static int __trace_eprobe_create(int argc, const char *argv[])
 	}
 
 	if (argc - 2 > MAX_TRACE_ARGS) {
+		trace_probe_log_set_index(2);
+		trace_probe_log_err(0, TOO_MANY_ARGS);
 		ret = -E2BIG;
 		goto error;
 	}
diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 985ff98272da..5d7ca80173ea 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -1199,8 +1199,11 @@ static int trace_fprobe_create_internal(int argc, const char *argv[],
 		argc = new_argc;
 		argv = new_argv;
 	}
-	if (argc > MAX_TRACE_ARGS)
+	if (argc > MAX_TRACE_ARGS) {
+		trace_probe_log_set_index(2);
+		trace_probe_log_err(0, TOO_MANY_ARGS);
 		return -E2BIG;
+	}
 
 	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
 	if (ret)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index d8d5f18a141a..8287b175667f 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1007,8 +1007,11 @@ static int trace_kprobe_create_internal(int argc, const char *argv[],
 		argc = new_argc;
 		argv = new_argv;
 	}
-	if (argc > MAX_TRACE_ARGS)
+	if (argc > MAX_TRACE_ARGS) {
+		trace_probe_log_set_index(2);
+		trace_probe_log_err(0, TOO_MANY_ARGS);
 		return -E2BIG;
+	}
 
 	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
 	if (ret)
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 8f58ee1e8858..2eeecb6c95ee 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:
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 96792bc4b092..854e5668f5ee 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -545,6 +545,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
 	C(BAD_BTF_TID,		"Failed to get BTF type info."),\
 	C(BAD_TYPE4STR,		"This type does not fit for string."),\
 	C(NEED_STRING_TYPE,	"$comm and immediate-string only accepts string type"),\
+	C(TOO_MANY_ARGS,	"Too many arguments are specified"),	\
 	C(TOO_MANY_EARGS,	"Too many entry arguments specified"),
 
 #undef C
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index ccc762fbb69c..3386439ec9f6 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -562,8 +562,14 @@ static int __trace_uprobe_create(int argc, const char **argv)
 
 	if (argc < 2)
 		return -ECANCELED;
-	if (argc - 2 > MAX_TRACE_ARGS)
+
+	trace_probe_log_init("trace_uprobe", argc, argv);
+
+	if (argc - 2 > MAX_TRACE_ARGS) {
+		trace_probe_log_set_index(2);
+		trace_probe_log_err(0, TOO_MANY_ARGS);
 		return -E2BIG;
+	}
 
 	if (argv[0][1] == ':')
 		event = &argv[0][2];
@@ -582,7 +588,6 @@ static int __trace_uprobe_create(int argc, const char **argv)
 		return -ECANCELED;
 	}
 
-	trace_probe_log_init("trace_uprobe", argc, argv);
 	trace_probe_log_set_index(1);	/* filename is the 2nd argument */
 
 	*arg++ = '\0';