[PATCH 2/8] ftrace: only allocate the ret_stack 'fp' field when needed

From: Josh Poimboeuf
Date: Fri Aug 19 2016 - 07:53:18 EST


This saves some memory when HAVE_FUNCTION_GRAPH_FP_TEST isn't defined.
On x86_64 with newer versions of gcc which have -mfentry, it saves 400
bytes per task.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
include/linux/ftrace.h | 2 ++
kernel/trace/trace_functions_graph.c | 2 ++
2 files changed, 4 insertions(+)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 7d565af..4ad9ccc 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -795,7 +795,9 @@ struct ftrace_ret_stack {
unsigned long func;
unsigned long long calltime;
unsigned long long subtime;
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
unsigned long fp;
+#endif
};

/*
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index fc173cd..0e03ed0 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -171,7 +171,9 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
current->ret_stack[index].func = func;
current->ret_stack[index].calltime = calltime;
current->ret_stack[index].subtime = 0;
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
current->ret_stack[index].fp = frame_pointer;
+#endif
*depth = current->curr_ret_stack;

return 0;
--
2.7.4