tracing/probes: Add symstr type for dynamic events

Add 'symstr' type for storing the kernel symbol as a string data
instead of the symbol address. This allows us to filter the
events by wildcard symbol name.

e.g.
  # echo 'e:wqfunc workqueue.workqueue_execute_start symname=$function:symstr' >> dynamic_events
  # cat events/eprobes/wqfunc/format
  name: wqfunc
  ID: 2110
  format:
  	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
  	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
  	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
  	field:int common_pid;	offset:4;	size:4;	signed:1;

  	field:__data_loc char[] symname;	offset:8;	size:4;	signed:1;

  print fmt: " symname=\"%s\"", __get_str(symname)

Note that there is already 'symbol' type which just change the
print format (so it still stores the symbol address in the tracing
ring buffer.) On the other hand, 'symstr' type stores the actual
"symbol+offset/size" data as a string.

Link: https://lore.kernel.org/all/166679930847.1528100.4124308529180235965.stgit@devnote3/

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

1 files changed, 44 insertions, 3 deletions

diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h
index b3bdb8ddb862..5cea672243f6 100644
--- a/kernel/trace/trace_probe_tmpl.h
+++ b/kernel/trace/trace_probe_tmpl.h
@@ -67,6 +67,37 @@ probe_mem_read(void *dest, void *src, size_t size);
 static nokprobe_inline int
 probe_mem_read_user(void *dest, void *src, size_t size);
 
+static nokprobe_inline int
+fetch_store_symstrlen(unsigned long addr)
+{
+	char namebuf[KSYM_SYMBOL_LEN];
+	int ret;
+
+	ret = sprint_symbol(namebuf, addr);
+	if (ret < 0)
+		return 0;
+
+	return ret + 1;
+}
+
+/*
+ * Fetch a null-terminated symbol string + offset. Caller MUST set *(u32 *)buf
+ * with max length and relative data location.
+ */
+static nokprobe_inline int
+fetch_store_symstring(unsigned long addr, void *dest, void *base)
+{
+	int maxlen = get_loc_len(*(u32 *)dest);
+	void *__dest;
+
+	if (unlikely(!maxlen))
+		return -ENOMEM;
+
+	__dest = get_loc_data(dest, base);
+
+	return sprint_symbol(__dest, addr);
+}
+
 /* From the 2nd stage, routine is same */
 static nokprobe_inline int
 process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
@@ -99,16 +130,22 @@ stage2:
 stage3:
 	/* 3rd stage: store value to buffer */
 	if (unlikely(!dest)) {
-		if (code->op == FETCH_OP_ST_STRING) {
+		switch (code->op) {
+		case FETCH_OP_ST_STRING:
 			ret = fetch_store_strlen(val + code->offset);
 			code++;
 			goto array;
-		} else if (code->op == FETCH_OP_ST_USTRING) {
+		case FETCH_OP_ST_USTRING:
 			ret += fetch_store_strlen_user(val + code->offset);
 			code++;
 			goto array;
-		} else
+		case FETCH_OP_ST_SYMSTR:
+			ret += fetch_store_symstrlen(val + code->offset);
+			code++;
+			goto array;
+		default:
 			return -EILSEQ;
+		}
 	}
 
 	switch (code->op) {
@@ -129,6 +166,10 @@ stage3:
 		loc = *(u32 *)dest;
 		ret = fetch_store_string_user(val + code->offset, dest, base);
 		break;
+	case FETCH_OP_ST_SYMSTR:
+		loc = *(u32 *)dest;
+		ret = fetch_store_symstring(val + code->offset, dest, base);
+		break;
 	default:
 		return -EILSEQ;
 	}