powerpc: ftrace, use probe_kernel API to modify code

Impact: use cleaner probe_kernel API over assembly

Using probe_kernel_read/write interface is a much cleaner approach
than the current assembly version.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 24c023a..1adfbb2 100644 (file)
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -9,6 +9,7 @@
 
 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
+#include <linux/uaccess.h>
 #include <linux/ftrace.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
@@ -72,45 +73,33 @@ static int
 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                   unsigned char *new_code)
 {
-       unsigned replaced;
-       unsigned old = *(unsigned *)old_code;
-       unsigned new = *(unsigned *)new_code;
-       int faulted = 0;
+       unsigned char replaced[MCOUNT_INSN_SIZE];
 
        /*
         * Note: Due to modules and __init, code can
         *  disappear and change, we need to protect against faulting
-        *  as well as code changing.
+        *  as well as code changing. We do this by using the
+        *  probe_kernel_* functions.
         *
         * No real locking needed, this code is run through
-        * kstop_machine.
+        * kstop_machine, or before SMP starts.
         */
-       asm volatile (
-               "1: lwz         %1, 0(%2)\n"
-               "   cmpw        %1, %5\n"
-               "   bne         2f\n"
-               "   stwu        %3, 0(%2)\n"
-               "2:\n"
-               ".section .fixup, \"ax\"\n"
-               "3:     li %0, 1\n"
-               "       b 2b\n"
-               ".previous\n"
-               ".section __ex_table,\"a\"\n"
-               _ASM_ALIGN "\n"
-               _ASM_PTR "1b, 3b\n"
-               ".previous"
-               : "=r"(faulted), "=r"(replaced)
-               : "r"(ip), "r"(new),
-                 "0"(faulted), "r"(old)
-               : "memory");
-
-       if (replaced != old && replaced != new)
-               faulted = 2;
-
-       if (!faulted)
-               flush_icache_range(ip, ip + 8);
-
-       return faulted;
+
+       /* read the text we want to modify */
+       if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+               return -EFAULT;
+
+       /* Make sure it is what we expect it to be */
+       if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
+               return -EINVAL;
+
+       /* replace the text with the new text */
+       if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
+               return -EPERM;
+
+       flush_icache_range(ip, ip + 8);
+
+       return 0;
 }
 
 static int test_24bit_addr(unsigned long ip, unsigned long addr)