x86, bts, ftrace: a BTS ftrace plug-in prototype

Impact: add new ftrace plugin

A prototype for a BTS ftrace plug-in.

The tracer collects branch trace in a cyclic buffer for each cpu.

The tracer is not configurable and the trace for each snapshot is
appended when doing cat /debug/tracing/trace.

This is a proof of concept that will be extended with future patches
to become a (hopefully) useful tool.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 12 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 717f9f045c6f..3abd645e8af2 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -27,6 +27,7 @@ enum trace_type {
         TRACE_BOOT_RET,
         TRACE_FN_RET,
         TRACE_USER_STACK,
+        TRACE_BTS,
 
         __TRACE_LAST_TYPE
 };
@@ -153,6 +154,12 @@ struct trace_branch {
         char                    correct;
 };
 
+struct bts_entry {
+        struct trace_entry      ent;
+        unsigned long           from;
+        unsigned long           to;
+};
+
 /*
  * trace_flag_type is an enumeration that holds different
  * states when a trace occurs. These are:
@@ -258,6 +265,7 @@ extern void __ftrace_bad_type(void);
                 IF_ASSIGN(var, ent, struct trace_boot_ret, TRACE_BOOT_RET);\
                 IF_ASSIGN(var, ent, struct trace_branch, TRACE_BRANCH); \
                 IF_ASSIGN(var, ent, struct ftrace_ret_entry, TRACE_FN_RET);\
+                IF_ASSIGN(var, ent, struct bts_entry, TRACE_BTS);\
                 __ftrace_bad_type();                                    \
         } while (0)
 
@@ -392,6 +400,10 @@ void trace_function(struct trace_array *tr,
 void
 trace_function_return(struct ftrace_retfunc *trace);
 
+void trace_bts(struct trace_array *tr,
+               unsigned long from,
+               unsigned long to);
+
 void tracing_start_cmdline_record(void);
 void tracing_stop_cmdline_record(void);
 void tracing_sched_switch_assign_trace(struct trace_array *tr);