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>

kernel/trace/trace_kprobe.c

@@ -366,7 +366,7 @@ static bool within_notrace_func(struct trace_kprobe *tk)
 /* Internal register function - just handle k*probes and flags */
 static int __register_trace_kprobe(struct trace_kprobe *tk)
 {
-	int ret;
+	int i, ret;
 
 	if (trace_probe_is_registered(&tk->tp))
 		return -EINVAL;
@@ -377,6 +377,12 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 		return -EINVAL;
 	}
 
+	for (i = 0; i < tk->tp.nr_args; i++) {
+		ret = traceprobe_update_arg(&tk->tp.args[i]);
+		if (ret)
+			return ret;
+	}
+
 	/* Set/clear disabled flag according to tp->flag */
 	if (trace_probe_is_enabled(&tk->tp))
 		tk->rp.kp.flags &= ~KPROBE_FLAG_DISABLED;
@@ -928,6 +934,7 @@ process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,
 {
 	unsigned long val;
 
+retry:
 	/* 1st stage: get value from context */
 	switch (code->op) {
 	case FETCH_OP_REG:
@@ -953,6 +960,9 @@ process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,
 		val = regs_get_kernel_argument(regs, code->param);
 		break;
 #endif
+	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
+		code++;
+		goto retry;
 	default:
 		return -EILSEQ;
 	}

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,

kernel/trace/trace_probe.h

@@ -100,6 +100,7 @@ enum fetch_op {
 	// Stage 5 (loop) op
 	FETCH_OP_LP_ARRAY,	/* Array: .param = loop count */
 	FETCH_OP_END,
+	FETCH_NOP_SYMBOL,	/* Unresolved Symbol holder */
 };
 
 struct fetch_insn {
@@ -116,6 +117,7 @@ struct fetch_insn {
 			unsigned char rshift;
 		};
 		unsigned long immediate;
+		void *data;
 	};
 };
 
@@ -276,7 +278,7 @@ extern int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
 extern int traceprobe_conflict_field_name(const char *name,
 			       struct probe_arg *args, int narg);
 
-extern void traceprobe_update_arg(struct probe_arg *arg);
+extern int traceprobe_update_arg(struct probe_arg *arg);
 extern void traceprobe_free_probe_arg(struct probe_arg *arg);
 
 extern int traceprobe_split_symbol_offset(char *symbol, long *offset);