ftrace: use dynamic patching for updating mcount calls

This patch replaces the indirect call to the mcount function
pointer with a direct call that will be patched by the
dynamic ftrace routines.

On boot up, the mcount function calls the ftace_stub function.
When the dynamic ftrace code is initialized, the ftrace_stub
is replaced with a call to the ftrace_record_ip, which records
the instruction pointers of the locations that call it.

Later, the ftraced daemon will call kstop_machine and patch all
the locations to nops.

When a ftrace is enabled, the original calls to mcount will now
be set top call ftrace_caller, which will do a direct call
to the registered ftrace function. This direct call is also patched
when the function that should be called is updated.

All patching is performed by a kstop_machine routine to prevent any
type of race conditions that is associated with modifying code
on the fly.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index d509ad6c9cb8..b0dd0093058f 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -56,9 +56,14 @@ struct dyn_ftrace {
 extern int ftrace_ip_converted(unsigned long ip);
 extern unsigned char *ftrace_nop_replace(void);
 extern unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr);
-extern int ftrace_dyn_arch_init(void);
+extern int ftrace_dyn_arch_init(void *data);
+extern int ftrace_mcount_set(unsigned long *data);
 extern int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                               unsigned char *new_code);
+extern int ftrace_update_ftrace_func(ftrace_func_t func);
+extern void ftrace_caller(void);
+extern void ftrace_call(void);
+extern void mcount_call(void);
 #endif
 
 #ifdef CONFIG_FRAME_POINTER