ftrace: use nops instead of jmp

This patch patches the call to mcount with nops instead
of a jmp over the mcount call.

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

2 files changed, 26 insertions, 18 deletions

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 65c7857a90dd..de240ba2e288 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -143,7 +143,7 @@ static const unsigned char *const p6_nops[ASM_NOP_MAX+1] = {
 #ifdef CONFIG_X86_64
 
 extern char __vsyscall_0;
-static inline const unsigned char*const * find_nop_table(void)
+const unsigned char *const *find_nop_table(void)
 {
         return boot_cpu_data.x86_vendor != X86_VENDOR_INTEL ||
                boot_cpu_data.x86 < 6 ? k8_nops : p6_nops;
@@ -162,7 +162,7 @@ static const struct nop {
         { -1, NULL }
 };
 
-static const unsigned char*const * find_nop_table(void)
+const unsigned char *const *find_nop_table(void)
 {
         const unsigned char *const *noptable = intel_nops;
         int i;
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 5dd58136ef02..2e060c58b860 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -16,11 +16,12 @@
 #include <linux/init.h>
 #include <linux/list.h>
 
-#define CALL_BACK               5
+#include <asm/alternative.h>
 
-#define JMPFWD                  0x03eb
+#define CALL_BACK               5
 
-static unsigned short ftrace_jmp = JMPFWD;
+/* Long is fine, even if it is only 4 bytes ;-) */
+static long *ftrace_nop;
 
 struct ftrace_record {
         struct dyn_ftrace       rec;
@@ -55,13 +56,13 @@ static struct ftrace_page	*ftrace_pages;
 notrace struct dyn_ftrace *ftrace_alloc_shutdown_node(unsigned long ip)
 {
         struct ftrace_record *rec;
-        unsigned short save;
+        unsigned long save;
 
         ip -= CALL_BACK;
-        save = *(short *)ip;
+        save = *(long *)ip;
 
         /* If this was already converted, skip it */
-        if (save == JMPFWD)
+        if (save == *ftrace_nop)
                 return NULL;
 
         if (ftrace_pages->index == ENTRIES_PER_PAGE) {
@@ -79,9 +80,10 @@ static int notrace
 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                    unsigned char *new_code)
 {
-        unsigned short old = *(unsigned short *)old_code;
-        unsigned short new = *(unsigned short *)new_code;
-        unsigned short replaced;
+        unsigned replaced;
+        unsigned old = *(unsigned *)old_code; /* 4 bytes */
+        unsigned new = *(unsigned *)new_code; /* 4 bytes */
+        unsigned char newch = new_code[4];
         int faulted = 0;
 
         /*
@@ -94,7 +96,9 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
          */
         asm volatile (
                 "1: lock\n"
-                "   cmpxchg %w3, (%2)\n"
+                "   cmpxchg %3, (%2)\n"
+                "   jnz 2f\n"
+                "   movb %b4, 4(%2)\n"
                 "2:\n"
                 ".section .fixup, \"ax\"\n"
                 "       movl $1, %0\n"
@@ -102,11 +106,12 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                 ".previous\n"
                 _ASM_EXTABLE(1b, 3b)
                 : "=r"(faulted), "=a"(replaced)
-                : "r"(ip), "r"(new), "0"(faulted), "a"(old)
+                : "r"(ip), "r"(new), "r"(newch),
+                  "0"(faulted), "a"(old)
                 : "memory");
         sync_core();
 
-        if (replaced != old)
+        if (replaced != old && replaced != new)
                 faulted = 2;
 
         return faulted;
@@ -132,7 +137,7 @@ notrace void ftrace_code_disable(struct dyn_ftrace *rec)
         /* move the IP back to the start of the call */
         ip -= CALL_BACK;
 
-        r->failed = ftrace_modify_code(ip, save.code, (char *)&ftrace_jmp);
+        r->failed = ftrace_modify_code(ip, save.code, (char *)ftrace_nop);
 }
 
 static void notrace ftrace_replace_code(int saved)
@@ -144,9 +149,9 @@ static void notrace ftrace_replace_code(int saved)
         int i;
 
         if (saved)
-                old = (char *)&ftrace_jmp;
+                old = (char *)ftrace_nop;
         else
-                new = (char *)&ftrace_jmp;
+                new = (char *)ftrace_nop;
 
         for (pg = ftrace_pages_start; pg; pg = pg->next) {
                 for (i = 0; i < pg->index; i++) {
@@ -194,12 +199,15 @@ notrace void ftrace_shutdown_replenish(void)
         ftrace_pages->next = (void *)get_zeroed_page(GFP_KERNEL);
 }
 
-notrace int ftrace_shutdown_arch_init(void)
+notrace int __init ftrace_shutdown_arch_init(void)
 {
+        const unsigned char *const *noptable = find_nop_table();
         struct ftrace_page *pg;
         int cnt;
         int i;
 
+        ftrace_nop = (unsigned long *)noptable[CALL_BACK];
+
         /* allocate a few pages */
         ftrace_pages_start = (void *)get_zeroed_page(GFP_KERNEL);
         if (!ftrace_pages_start)