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>
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 65c7857..de240ba 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -143,7 +143,7 @@
#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 @@
{ -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 5dd5813..2e060c5 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>
+#include <asm/alternative.h>
+
#define CALL_BACK 5
-#define JMPFWD 0x03eb
-
-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 @@
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 @@
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 @@
*/
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 @@
".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 @@
/* 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 @@
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 @@
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)
diff --git a/include/asm-x86/alternative.h b/include/asm-x86/alternative.h
index 1f6a9ca..f6aa18e 100644
--- a/include/asm-x86/alternative.h
+++ b/include/asm-x86/alternative.h
@@ -72,6 +72,8 @@
static inline void alternatives_smp_switch(int smp) {}
#endif /* CONFIG_SMP */
+const unsigned char *const *find_nop_table(void);
+
/*
* Alternative instructions for different CPU types or capabilities.
*
