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>
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index b69795e..9f44623 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -109,10 +109,49 @@
return faulted;
}
-int __init ftrace_dyn_arch_init(void)
+notrace int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+ unsigned long ip = (unsigned long)(&ftrace_call);
+ unsigned char old[5], *new;
+ int ret;
+
+ ip += CALL_BACK;
+
+ memcpy(old, &ftrace_call, 5);
+ new = ftrace_call_replace(ip, (unsigned long)func);
+ ret = ftrace_modify_code(ip, old, new);
+
+ return ret;
+}
+
+notrace int ftrace_mcount_set(unsigned long *data)
+{
+ unsigned long ip = (long)(&mcount_call);
+ unsigned long *addr = data;
+ unsigned char old[5], *new;
+
+ /* ip is at the location, but modify code will subtact this */
+ ip += CALL_BACK;
+
+ /*
+ * Replace the mcount stub with a pointer to the
+ * ip recorder function.
+ */
+ memcpy(old, &mcount_call, 5);
+ new = ftrace_call_replace(ip, *addr);
+ *addr = ftrace_modify_code(ip, old, new);
+
+ return 0;
+}
+
+int __init ftrace_dyn_arch_init(void *data)
{
const unsigned char *const *noptable = find_nop_table();
+ /* This is running in kstop_machine */
+
+ ftrace_mcount_set(data);
+
ftrace_nop = (unsigned long *)noptable[CALL_BACK];
return 0;