tracing/kprobes: Allow kprobe-events to record module symbol

Allow kprobe-events to record module symbols.

Since data symbols in a non-loaded module doesn't exist, it fails to
define such symbol as an argument of kprobe-event. But if the kprobe
event is defined on that module, we can defer to resolve the symbol
address.

Note that if given symbol is not found, the event is kept unavailable.
User can enable it but the event is not recorded.

Link: http://lkml.kernel.org/r/153547312336.26502.11432902826345374463.stgit@devbox

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 54 insertions, 8 deletions

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 333cda6d2633..5b3d573b3dcf 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -251,16 +251,16 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 			if (!(flags & TPARG_FL_KERNEL))
 				return -EINVAL;
 
-			ret = traceprobe_split_symbol_offset(arg + 1, &offset);
-			if (ret)
-				break;
+			/* Preserve symbol for updating */
+			code->op = FETCH_NOP_SYMBOL;
+			code->data = kstrdup(arg + 1, GFP_KERNEL);
+			if (!code->data)
+				return -ENOMEM;
+			if (++code == end)
+				return -E2BIG;
 
 			code->op = FETCH_OP_IMM;
-			code->immediate =
-				(unsigned long)kallsyms_lookup_name(arg + 1);
-			if (!code->immediate)
-				return -ENOENT;
-			code->immediate += offset;
+			code->immediate = 0;
 		}
 		/* These are fetching from memory */
 		if (++code == end)
@@ -480,6 +480,11 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
 		memcpy(parg->code, tmp, sizeof(*code) * (code - tmp + 1));
 
 fail:
+	if (ret) {
+		for (code = tmp; code < tmp + FETCH_INSN_MAX; code++)
+			if (code->op == FETCH_NOP_SYMBOL)
+				kfree(code->data);
+	}
 	kfree(tmp);
 
 	return ret;
@@ -504,12 +509,53 @@ int traceprobe_conflict_field_name(const char *name,
 
 void traceprobe_free_probe_arg(struct probe_arg *arg)
 {
+	struct fetch_insn *code = arg->code;
+
+	while (code && code->op != FETCH_OP_END) {
+		if (code->op == FETCH_NOP_SYMBOL)
+			kfree(code->data);
+		code++;
+	}
 	kfree(arg->code);
 	kfree(arg->name);
 	kfree(arg->comm);
 	kfree(arg->fmt);
 }
 
+int traceprobe_update_arg(struct probe_arg *arg)
+{
+	struct fetch_insn *code = arg->code;
+	long offset;
+	char *tmp;
+	char c;
+	int ret = 0;
+
+	while (code && code->op != FETCH_OP_END) {
+		if (code->op == FETCH_NOP_SYMBOL) {
+			if (code[1].op != FETCH_OP_IMM)
+				return -EINVAL;
+
+			tmp = strpbrk("+-", code->data);
+			if (tmp)
+				c = *tmp;
+			ret = traceprobe_split_symbol_offset(code->data,
+							     &offset);
+			if (ret)
+				return ret;
+
+			code[1].immediate =
+				(unsigned long)kallsyms_lookup_name(code->data);
+			if (tmp)
+				*tmp = c;
+			if (!code[1].immediate)
+				return -ENOENT;
+			code[1].immediate += offset;
+		}
+		code++;
+	}
+	return 0;
+}
+
 /* When len=0, we just calculate the needed length */
 #define LEN_OR_ZERO (len ? len - pos : 0)
 static int __set_print_fmt(struct trace_probe *tp, char *buf, int len,