[RFC PATCH 20/32] function_graph: Pass the size of reserved data when retrieving it

["Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Make the fgraph_retrieve_data() returns the reverved data size via
size_byte parameter.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 include/linux/ftrace.h        |    2 +-
 kernel/trace/fgraph.c         |    5 ++++-
 kernel/trace/trace_selftest.c |   10 +++++++++-
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 115758fe9fec..2e24a2611ca8 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -1050,7 +1050,7 @@ struct fgraph_ops {
 };
 
 void *fgraph_reserve_data(int size_bytes);
-void *fgraph_retrieve_data(void);
+void *fgraph_retrieve_data(int *size_bytes);
 
 /*
  * Stack of return addresses for functions
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index e51695441476..0b8a1daef733 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -289,6 +289,7 @@ void *fgraph_reserve_data(int size_bytes)
 
 /**
  * fgraph_retrieve_data - Retrieve stored data from fgraph_reserve_data()
+ * @size_bytes: pointer to retrieved data size.
  *
  * This is to be called by a fgraph_ops retfunc(), to retrieve data that
  * was stored by the fgraph_ops entryfunc() on the function entry.
@@ -300,7 +301,7 @@ void *fgraph_reserve_data(int size_bytes)
  *    matching entryfunc() for the retfunc() this is called from.
  *   Or NULL if there was nothing stored.
  */
-void *fgraph_retrieve_data(void)
+void *fgraph_retrieve_data(int *size_bytes)
 {
 	unsigned long val;
 	int curr_ret_stack = current->curr_ret_stack;
@@ -313,6 +314,8 @@ void *fgraph_retrieve_data(void)
 	val = current->ret_stack[curr_ret_stack - 2];
 	if (__get_type(val) != FGRAPH_TYPE_DATA)
 		return NULL;
+	if (size_bytes)
+		*size_bytes = (__get_data(val) - 1) * sizeof(long);
 
 	return &current->ret_stack[curr_ret_stack -
 				   (__get_data(val) + 1)];
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 14966d8509ed..c656ec5b3348 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -807,15 +807,23 @@ static __init void store_return(struct ftrace_graph_ret *trace,
 	const char *type = fgraph_store_type_name;
 	long long expect = 0;
 	long long found = -1;
+	int size;
 	char *p;
 
-	p = fgraph_retrieve_data();
+	p = fgraph_retrieve_data(&size);
 	if (!p) {
 		snprintf(fgraph_error_str_buf, sizeof(fgraph_error_str_buf),
 			 "Failed to retrieve %s\n", type);
 		fgraph_error_str = fgraph_error_str_buf;
 		return;
 	}
+	if (fgraph_store_size > size) {
+		snprintf(fgraph_error_str_buf, sizeof(fgraph_error_str_buf),
+			 "Retrieved size %d is smaller than expected %d\n",
+			 size, (int)fgraph_store_size);
+		fgraph_error_str = fgraph_error_str_buf;
+		return;
+	}
 
 	switch (fgraph_store_size) {
 	case 1: