[RFC PATCH] tracing/kprobes: Avoid parsing symbol+offset when updating arguments

[Masami Hiramatsu]

Introduce symbol_offset data structure for avoiding symbol+offset
parsing when updating arguments.

For kprobe events, "@symbol+offset" is supported, that requires
to be updated when new module is loaded because @symbol address
can be solved at that point. Currently kprobe events saves
the "symbol+offset" string and parse it repeatedly, but that
is inefficient.
This introduces symbol_offset data structure which can save the
offset and symbol separated, so that we don't need to parse it
anymore.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 kernel/trace/trace_probe.c |   49 +++++++++++++++++++++++++-------------------
 kernel/trace/trace_probe.h |    7 +++++-
 2 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index bd30e9398d2a..0a3af7d6e133 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -201,6 +201,26 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 	return ret;
 }
 
+static struct symbol_offset *allocate_symbol_offset(char *sym_offs_str)
+{
+	int ret;
+	long offset = 0;
+	struct symbol_offset *sof;
+
+	ret = traceprobe_split_symbol_offset(sym_offs_str, &offset);
+	if (ret)
+		return ERR_PTR(ret);
+
+	sof = kzalloc(sizeof(struct symbol_offset) + strlen(sym_offs_str) + 1,
+			GFP_KERNEL);
+	if (!sof)
+		return ERR_PTR(-ENOMEM);
+
+	sof->offset = offset;
+	strcpy(sof->symbol, sym_offs_str);
+	return sof;
+}
+
 /* Recursive argument parser */
 static int
 parse_probe_arg(char *arg, const struct fetch_type *type,
@@ -253,9 +273,9 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 
 			/* Preserve symbol for updating */
 			code->op = FETCH_NOP_SYMBOL;
-			code->data = kstrdup(arg + 1, GFP_KERNEL);
-			if (!code->data)
-				return -ENOMEM;
+			code->symoffs = allocate_symbol_offset(arg + 1);
+			if (IS_ERR(code->symoffs))
+				return PTR_ERR(code->symoffs);
 			if (++code == end)
 				return -E2BIG;
 
@@ -483,7 +503,7 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
 	if (ret) {
 		for (code = tmp; code < tmp + FETCH_INSN_MAX; code++)
 			if (code->op == FETCH_NOP_SYMBOL)
-				kfree(code->data);
+				kfree(code->symoffs);
 	}
 	kfree(tmp);
 
@@ -513,7 +533,7 @@ void traceprobe_free_probe_arg(struct probe_arg *arg)
 
 	while (code && code->op != FETCH_OP_END) {
 		if (code->op == FETCH_NOP_SYMBOL)
-			kfree(code->data);
+			kfree(code->symoffs);
 		code++;
 	}
 	kfree(arg->code);
@@ -525,31 +545,18 @@ void traceprobe_free_probe_arg(struct probe_arg *arg)
 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;
+				(unsigned long)kallsyms_lookup_name(
+						code->symoffs->symbol);
 			if (!code[1].immediate)
 				return -ENOENT;
-			code[1].immediate += offset;
+			code[1].immediate += code->symoffs->offset;
 		}
 		code++;
 	}
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 974afc1a3e73..942424d05427 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -103,6 +103,11 @@ enum fetch_op {
 	FETCH_NOP_SYMBOL,	/* Unresolved Symbol holder */
 };
 
+struct symbol_offset {
+	long offset;
+	char symbol[];
+};
+
 struct fetch_insn {
 	enum fetch_op op;
 	union {
@@ -117,7 +122,7 @@ struct fetch_insn {
 			unsigned char rshift;
 		};
 		unsigned long immediate;
-		void *data;
+		struct symbol_offset *symoffs;
 	};
 };