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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>
This commit is contained in:
Steven Rostedt 2008-05-12 21:20:43 +02:00 committed by Thomas Gleixner
parent b0fc494fae
commit dfa60aba04
3 changed files with 28 additions and 18 deletions
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4
arch/x86/kernel/alternative.c
View File

@ -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;

40
arch/x86/kernel/ftrace.c
View File

@ -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 @@ 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)

2
include/asm-x86/alternative.h
View File

@ -72,6 +72,8 @@ static inline void alternatives_smp_module_del(struct module *mod) {}
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.
*