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, 44 insertions, 3 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index f47b9b5440d2..e6517ce0b824 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1110,10 +1110,50 @@ ENDPROC(xen_failsafe_callback)
 #endif  /* CONFIG_XEN */
 
 #ifdef CONFIG_FTRACE
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+ENTRY(mcount)
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        movl 0xc(%esp), %eax
+
+.globl mcount_call
+mcount_call:
+        call ftrace_stub
+
+        popl %edx
+        popl %ecx
+        popl %eax
+
+        ret
+END(mcount)
+
+ENTRY(ftrace_caller)
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        movl 0xc(%esp), %eax
+        movl 0x4(%ebp), %edx
+
+.globl ftrace_call
+ftrace_call:
+        call ftrace_stub
+
+        popl %edx
+        popl %ecx
+        popl %eax
+
+.globl ftrace_stub
+ftrace_stub:
+        ret
+END(ftrace_caller)
+
+#else /* ! CONFIG_DYNAMIC_FTRACE */
+
 ENTRY(mcount)
         cmpl $ftrace_stub, ftrace_trace_function
         jnz trace
-
 .globl ftrace_stub
 ftrace_stub:
         ret
@@ -1126,7 +1166,7 @@ trace:
         movl 0xc(%esp), %eax
         movl 0x4(%ebp), %edx
 
-        call   *ftrace_trace_function
+        call *ftrace_trace_function
 
         popl %edx
         popl %ecx
@@ -1134,7 +1174,8 @@ trace:
 
         jmp ftrace_stub
 END(mcount)
-#endif
+#endif /* CONFIG_DYNAMIC_FTRACE */
+#endif /* CONFIG_FTRACE */
 
 .section .rodata,"a"
 #include "syscall_table_32.S"