ftrace: mcount call site on boot nops core

This is the infrastructure to the converting the mcount call sites
recorded by the __mcount_loc section into nops on boot. It also allows
for using these sites to enable tracing as normal. When the __mcount_loc
section is used, the "ftraced" kernel thread is disabled.

This uses the current infrastructure to record the mcount call sites
as well as convert them to nops. The mcount function is kept as a stub
on boot up and not converted to the ftrace_record_ip function. We use the
ftrace_record_ip to only record from the table.

This patch does not handle modules. That comes with a later patch.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 16 insertions, 0 deletions

diff --git a/include/asm-x86/ftrace.h b/include/asm-x86/ftrace.h
index be0e004ad148..1bb6f9bbe1ab 100644
--- a/include/asm-x86/ftrace.h
+++ b/include/asm-x86/ftrace.h
@@ -7,6 +7,16 @@
 
 #ifndef __ASSEMBLY__
 extern void mcount(void);
+
+static inline unsigned long ftrace_call_adjust(unsigned long addr)
+{
+        /*
+         * call mcount is "e8 <4 byte offset>"
+         * The addr points to the 4 byte offset and the caller of this
+         * function wants the pointer to e8. Simply subtract one.
+         */
+        return addr - 1;
+}
 #endif
 
 #endif /* CONFIG_FTRACE */
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index bb384068272e..d4d6ab453b78 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -162,4 +162,10 @@ static inline void
 ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3) { }
 #endif
 
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+extern void ftrace_init(void);
+#else
+static inline void ftrace_init(void) { }
+#endif
+
 #endif /* _LINUX_FTRACE_H */