linux-kernel - [for-next][PATCH 03/24] fgraph: Add comment to describe ftrace_graph_get_ret

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Message-Id: <20181221175655.732569750@goodmis.org>
Date:   Fri, 21 Dec 2018 12:56:21 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [for-next][PATCH 03/24] fgraph: Add comment to describe ftrace_graph_get_ret_stack

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

The ret_stack should not be accessed directly via the curr_ret_stack
variable on the task_struct. This is because the ret_stack is going to be
converted into a series of longs and not an array of ret_stack structures.
The way that a ret_stack should be retrieved is via the
ftrace_graph_get_ret_stack structure, but it needs to be documented on how
to use it.

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/fgraph.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index a3704ec8b599..d4f04f0ca646 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -232,6 +232,17 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
 	return ret;
 }
 
+/**
+ * ftrace_graph_get_ret_stack - return the entry of the shadow stack
+ * @task: The task to read the shadow stack from
+ * @idx: Index down the shadow stack
+ *
+ * Return the ret_struct on the shadow stack of the @task at the
+ * call graph at @idx starting with zero. If @idx is zero, it
+ * will return the last saved ret_stack entry. If it is greater than
+ * zero, it will return the corresponding ret_stack for the depth
+ * of saved return addresses.
+ */
 struct ftrace_ret_stack *
 ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
 {
-- 
2.19.2