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Commit dfa60aba authored by Steven Rostedt's avatar Steven Rostedt Committed by Thomas Gleixner
Browse files

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: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent b0fc494f

arch/x86/kernel/alternative.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

arch/x86/kernel/ftrace.c

+24 −16
Original line number Diff line number Diff line
@@ -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)

include/asm-x86/alternative.h

+2 −0
Original line number Diff line number Diff line
@@ -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.

 *