tracing/probes: Support $argN in return probe (kprobe and fprobe)

Support accessing $argN in the return probe events. This will help users to
record entry data in function return (exit) event for simplfing the function
entry/exit information in one event, and record the result values (e.g.
allocated object/initialized object) at function exit.

For example, if we have a function `int init_foo(struct foo *obj, int param)`
sometimes we want to check how `obj` is initialized. In such case, we can
define a new return event like below;

 # echo 'r init_foo retval=$retval param=$arg2 field1=+0($arg1)' >> kprobe_events

Thus it records the function parameter `param` and its result `obj->field1`
(the dereference will be done in the function exit timing) value at once.

This also support fprobe, BTF args and'$arg*'. So if CONFIG_DEBUG_INFO_BTF
is enabled, we can trace both function parameters and the return value
by following command.

 # echo 'f target_function%return $arg* $retval' >> dynamic_events

Link: https://lore.kernel.org/all/170952365552.229804.224112990211602895.stgit@devnote2/

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

1 files changed, 27 insertions, 1 deletions

diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index ed8d1052f8a7..cef3a50628a3 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -92,6 +92,7 @@ enum fetch_op {
 	FETCH_OP_ARG,		/* Function argument : .param */
 	FETCH_OP_FOFFS,		/* File offset: .immediate */
 	FETCH_OP_DATA,		/* Allocated data: .data */
+	FETCH_OP_EDATA,		/* Entry data: .offset */
 	// Stage 2 (dereference) op
 	FETCH_OP_DEREF,		/* Dereference: .offset */
 	FETCH_OP_UDEREF,	/* User-space Dereference: .offset */
@@ -102,6 +103,7 @@ enum fetch_op {
 	FETCH_OP_ST_STRING,	/* String: .offset, .size */
 	FETCH_OP_ST_USTRING,	/* User String: .offset, .size */
 	FETCH_OP_ST_SYMSTR,	/* Kernel Symbol String: .offset, .size */
+	FETCH_OP_ST_EDATA,	/* Store Entry Data: .offset */
 	// Stage 4 (modify) op
 	FETCH_OP_MOD_BF,	/* Bitfield: .basesize, .lshift, .rshift */
 	// Stage 5 (loop) op
@@ -232,6 +234,11 @@ struct probe_arg {
 	const struct fetch_type	*type;	/* Type of this argument */
 };
 
+struct probe_entry_arg {
+	struct fetch_insn	*code;
+	unsigned int		size;	/* The entry data size */
+};
+
 struct trace_uprobe_filter {
 	rwlock_t		rwlock;
 	int			nr_systemwide;
@@ -253,6 +260,7 @@ struct trace_probe {
 	struct trace_probe_event	*event;
 	ssize_t				size;	/* trace entry size */
 	unsigned int			nr_args;
+	struct probe_entry_arg		*entry_arg;	/* This is only for return probe */
 	struct probe_arg		args[];
 };
 
@@ -355,6 +363,18 @@ int trace_probe_create(const char *raw_command, int (*createfn)(int, const char
 int trace_probe_print_args(struct trace_seq *s, struct probe_arg *args, int nr_args,
 		 u8 *data, void *field);
 
+#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
+int traceprobe_get_entry_data_size(struct trace_probe *tp);
+/* This is a runtime function to store entry data */
+void store_trace_entry_data(void *edata, struct trace_probe *tp, struct pt_regs *regs);
+#else /* !CONFIG_HAVE_FUNCTION_ARG_ACCESS_API */
+static inline int traceprobe_get_entry_data_size(struct trace_probe *tp)
+{
+	return 0;
+}
+#define store_trace_entry_data(edata, tp, regs) do { } while (0)
+#endif
+
 #define trace_probe_for_each_link(pos, tp)	\
 	list_for_each_entry(pos, &(tp)->event->files, list)
 #define trace_probe_for_each_link_rcu(pos, tp)	\
@@ -381,6 +401,11 @@ static inline bool tparg_is_function_entry(unsigned int flags)
 	return (flags & TPARG_FL_LOC_MASK) == (TPARG_FL_KERNEL | TPARG_FL_FENTRY);
 }
 
+static inline bool tparg_is_function_return(unsigned int flags)
+{
+	return (flags & TPARG_FL_LOC_MASK) == (TPARG_FL_KERNEL | TPARG_FL_RETURN);
+}
+
 struct traceprobe_parse_context {
 	struct trace_event_call *event;
 	/* BTF related parameters */
@@ -392,6 +417,7 @@ struct traceprobe_parse_context {
 	const struct btf_type *last_type;	/* Saved type */
 	u32 last_bitoffs;		/* Saved bitoffs */
 	u32 last_bitsize;		/* Saved bitsize */
+	struct trace_probe *tp;
 	unsigned int flags;
 	int offset;
 };
@@ -506,7 +532,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
 	C(NO_BTFARG,		"This variable is not found at this probe point"),\
 	C(NO_BTF_ENTRY,		"No BTF entry for this probe point"),	\
 	C(BAD_VAR_ARGS,		"$arg* must be an independent parameter without name etc."),\
-	C(NOFENTRY_ARGS,	"$arg* can be used only on function entry"),	\
+	C(NOFENTRY_ARGS,	"$arg* can be used only on function entry or exit"),	\
 	C(DOUBLE_ARGS,		"$arg* can be used only once in the parameters"),	\
 	C(ARGS_2LONG,		"$arg* failed because the argument list is too long"),	\
 	C(ARGIDX_2BIG,		"$argN index is too big"),		\