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, 29 insertions, 15 deletions

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 36dff277de46..dfec4af857b4 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -76,9 +76,11 @@ const char PRINT_TYPE_FMT_NAME(string)[] = "\\\"%s\\\"";
 /* Fetch type information table */
 static const struct fetch_type probe_fetch_types[] = {
 	/* Special types */
-	__ASSIGN_FETCH_TYPE("string", string, string, sizeof(u32), 1,
+	__ASSIGN_FETCH_TYPE("string", string, string, sizeof(u32), 1, 1,
 			    "__data_loc char[]"),
-	__ASSIGN_FETCH_TYPE("ustring", string, string, sizeof(u32), 1,
+	__ASSIGN_FETCH_TYPE("ustring", string, string, sizeof(u32), 1, 1,
+			    "__data_loc char[]"),
+	__ASSIGN_FETCH_TYPE("symstr", string, string, sizeof(u32), 1, 1,
 			    "__data_loc char[]"),
 	/* Basic types */
 	ASSIGN_FETCH_TYPE(u8,  u8,  0),
@@ -662,16 +664,26 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 
 	ret = -EINVAL;
 	/* Store operation */
-	if (!strcmp(parg->type->name, "string") ||
-	    !strcmp(parg->type->name, "ustring")) {
-		if (code->op != FETCH_OP_DEREF && code->op != FETCH_OP_UDEREF &&
-		    code->op != FETCH_OP_IMM && code->op != FETCH_OP_COMM &&
-		    code->op != FETCH_OP_DATA && code->op != FETCH_OP_TP_ARG) {
-			trace_probe_log_err(offset + (t ? (t - arg) : 0),
-					    BAD_STRING);
-			goto fail;
+	if (parg->type->is_string) {
+		if (!strcmp(parg->type->name, "symstr")) {
+			if (code->op != FETCH_OP_REG && code->op != FETCH_OP_STACK &&
+			    code->op != FETCH_OP_RETVAL && code->op != FETCH_OP_ARG &&
+			    code->op != FETCH_OP_DEREF && code->op != FETCH_OP_TP_ARG) {
+				trace_probe_log_err(offset + (t ? (t - arg) : 0),
+						    BAD_SYMSTRING);
+				goto fail;
+			}
+		} else {
+			if (code->op != FETCH_OP_DEREF && code->op != FETCH_OP_UDEREF &&
+			    code->op != FETCH_OP_IMM && code->op != FETCH_OP_COMM &&
+			    code->op != FETCH_OP_DATA && code->op != FETCH_OP_TP_ARG) {
+				trace_probe_log_err(offset + (t ? (t - arg) : 0),
+						    BAD_STRING);
+				goto fail;
+			}
 		}
-		if ((code->op == FETCH_OP_IMM || code->op == FETCH_OP_COMM ||
+		if (!strcmp(parg->type->name, "symstr") ||
+		    (code->op == FETCH_OP_IMM || code->op == FETCH_OP_COMM ||
 		     code->op == FETCH_OP_DATA) || code->op == FETCH_OP_TP_ARG ||
 		     parg->count) {
 			/*
@@ -679,6 +691,8 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 			 * must be kept, and if parg->count != 0, this is an
 			 * array of string pointers instead of string address
 			 * itself.
+			 * For the symstr, it doesn't need to dereference, thus
+			 * it just get the value.
 			 */
 			code++;
 			if (code->op != FETCH_OP_NOP) {
@@ -690,6 +704,8 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 		if (!strcmp(parg->type->name, "ustring") ||
 		    code->op == FETCH_OP_UDEREF)
 			code->op = FETCH_OP_ST_USTRING;
+		else if (!strcmp(parg->type->name, "symstr"))
+			code->op = FETCH_OP_ST_SYMSTR;
 		else
 			code->op = FETCH_OP_ST_STRING;
 		code->size = parg->type->size;
@@ -919,8 +935,7 @@ static int __set_print_fmt(struct trace_probe *tp, char *buf, int len,
 	for (i = 0; i < tp->nr_args; i++) {
 		parg = tp->args + i;
 		if (parg->count) {
-			if ((strcmp(parg->type->name, "string") == 0) ||
-			    (strcmp(parg->type->name, "ustring") == 0))
+			if (parg->type->is_string)
 				fmt = ", __get_str(%s[%d])";
 			else
 				fmt = ", REC->%s[%d]";
@@ -928,8 +943,7 @@ static int __set_print_fmt(struct trace_probe *tp, char *buf, int len,
 				pos += snprintf(buf + pos, LEN_OR_ZERO,
 						fmt, parg->name, j);
 		} else {
-			if ((strcmp(parg->type->name, "string") == 0) ||
-			    (strcmp(parg->type->name, "ustring") == 0))
+			if (parg->type->is_string)
 				fmt = ", __get_str(%s)";
 			else
 				fmt = ", REC->%s";