[PATCH 4/7] Add print_function_args()

[Sven Schnelle <svens@xxxxxxxxxxxxx>]

Add a function to decode argument types with the help of BTF. Will
be used to display arguments in the function and function graph
tracer.

Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
---
 kernel/trace/trace_output.c | 68 +++++++++++++++++++++++++++++++++++++
 kernel/trace/trace_output.h |  9 +++++
 2 files changed, 77 insertions(+)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d8b302d01083..70405c4cceb6 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -12,8 +12,11 @@
 #include <linux/sched/clock.h>
 #include <linux/sched/mm.h>
 #include <linux/idr.h>
+#include <linux/btf.h>
+#include <linux/bpf.h>
 
 #include "trace_output.h"
+#include "trace_btf.h"
 
 /* must be a power of 2 */
 #define EVENT_HASHSIZE	128
@@ -669,6 +672,71 @@ int trace_print_lat_context(struct trace_iterator *iter)
 	return !trace_seq_has_overflowed(s);
 }
 
+#ifdef CONFIG_FUNCTION_TRACE_ARGS
+void print_function_args(struct trace_seq *s, struct ftrace_regs *fregs,
+			 unsigned long func)
+{
+	const struct btf_param *param;
+	const struct btf_type *t;
+	const char *param_name;
+	char name[KSYM_NAME_LEN];
+	unsigned long arg;
+	struct btf *btf;
+	s32 tid, nr = 0;
+	int i;
+
+	trace_seq_printf(s, "(");
+
+	if (!ftrace_regs_has_args(fregs))
+		goto out;
+	if (lookup_symbol_name(func, name))
+		goto out;
+
+	btf = bpf_get_btf_vmlinux();
+	if (IS_ERR_OR_NULL(btf))
+		goto out;
+
+	t = btf_find_func_proto(name, &btf);
+	if (IS_ERR_OR_NULL(t))
+		goto out;
+
+	param = btf_get_func_param(t, &nr);
+	if (!param)
+		goto out_put;
+
+	for (i = 0; i < nr; i++) {
+		arg = ftrace_regs_get_argument(fregs, i);
+
+		param_name = btf_name_by_offset(btf, param[i].name_off);
+		if (param_name)
+			trace_seq_printf(s, "%s = ", param_name);
+		t = btf_type_skip_modifiers(btf, param[i].type, &tid);
+		if (!t)
+			continue;
+		switch (BTF_INFO_KIND(t->info)) {
+		case BTF_KIND_PTR:
+			trace_seq_printf(s, "0x%lx", arg);
+			break;
+		case BTF_KIND_INT:
+			trace_seq_printf(s, "%ld", arg);
+			break;
+		case BTF_KIND_ENUM:
+			trace_seq_printf(s, "%ld", arg);
+			break;
+		default:
+			trace_seq_printf(s, "0x%lx (%d)", arg, BTF_INFO_KIND(param[i].type));
+			break;
+		}
+		if (i < nr - 1)
+			trace_seq_printf(s, ", ");
+	}
+out_put:
+	btf_put(btf);
+out:
+	trace_seq_printf(s, ")");
+}
+#endif
+
 /**
  * ftrace_find_event - find a registered event
  * @type: the type of event to look for
diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h
index dca40f1f1da4..a21d8ce606f7 100644
--- a/kernel/trace/trace_output.h
+++ b/kernel/trace/trace_output.h
@@ -41,5 +41,14 @@ extern struct rw_semaphore trace_event_sem;
 #define SEQ_PUT_HEX_FIELD(s, x)				\
 	trace_seq_putmem_hex(s, &(x), sizeof(x))
 
+#ifdef CONFIG_FUNCTION_TRACE_ARGS
+void print_function_args(struct trace_seq *s, struct ftrace_regs *fregs,
+			 unsigned long func);
+#else
+static inline void print_function_args(struct trace_seq *s, struct ftrace_regs *fregs,
+				       unsigned long func) {
+	trace_seq_puts(s, "()");
+}
+#endif
 #endif
 
-- 
2.43.0