2 * Code for replacing ftrace calls with jumps.
4 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
6 * Thanks goes to Ingo Molnar, for suggesting the idea.
7 * Mathieu Desnoyers, for suggesting postponing the modifications.
8 * Arjan van de Ven, for keeping me straight, and explaining to me
9 * the dangers of modifying code on the run.
12 #include <linux/spinlock.h>
13 #include <linux/hardirq.h>
14 #include <linux/uaccess.h>
15 #include <linux/ftrace.h>
16 #include <linux/percpu.h>
17 #include <linux/sched.h>
18 #include <linux/init.h>
19 #include <linux/list.h>
21 #include <asm/cacheflush.h>
22 #include <asm/ftrace.h>
23 #include <linux/ftrace.h>
28 #ifdef CONFIG_DYNAMIC_FTRACE
30 int ftrace_arch_code_modify_prepare(void)
36 int ftrace_arch_code_modify_post_process(void)
42 union ftrace_code_union {
43 char code[MCOUNT_INSN_SIZE];
47 } __attribute__((packed));
50 static int ftrace_calc_offset(long ip, long addr)
52 return (int)(addr - ip);
55 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
57 static union ftrace_code_union calc;
60 calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
63 * No locking needed, this must be called via kstop_machine
64 * which in essence is like running on a uniprocessor machine.
70 * Modifying code must take extra care. On an SMP machine, if
71 * the code being modified is also being executed on another CPU
72 * that CPU will have undefined results and possibly take a GPF.
73 * We use kstop_machine to stop other CPUS from exectuing code.
74 * But this does not stop NMIs from happening. We still need
75 * to protect against that. We separate out the modification of
76 * the code to take care of this.
78 * Two buffers are added: An IP buffer and a "code" buffer.
80 * 1) Put the instruction pointer into the IP buffer
81 * and the new code into the "code" buffer.
82 * 2) Set a flag that says we are modifying code
83 * 3) Wait for any running NMIs to finish.
86 * 6) Wait for any running NMIs to finish.
88 * If an NMI is executed, the first thing it does is to call
89 * "ftrace_nmi_enter". This will check if the flag is set to write
90 * and if it is, it will write what is in the IP and "code" buffers.
92 * The trick is, it does not matter if everyone is writing the same
93 * content to the code location. Also, if a CPU is executing code
94 * it is OK to write to that code location if the contents being written
95 * are the same as what exists.
98 static atomic_t nmi_running = ATOMIC_INIT(0);
99 static int mod_code_status; /* holds return value of text write */
100 static int mod_code_write; /* set when NMI should do the write */
101 static void *mod_code_ip; /* holds the IP to write to */
102 static void *mod_code_newcode; /* holds the text to write to the IP */
104 static unsigned nmi_wait_count;
105 static atomic_t nmi_update_count = ATOMIC_INIT(0);
107 int ftrace_arch_read_dyn_info(char *buf, int size)
111 r = snprintf(buf, size, "%u %u",
113 atomic_read(&nmi_update_count));
117 static void ftrace_mod_code(void)
120 * Yes, more than one CPU process can be writing to mod_code_status.
121 * (and the code itself)
122 * But if one were to fail, then they all should, and if one were
123 * to succeed, then they all should.
125 mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
128 /* if we fail, then kill any new writers */
133 void ftrace_nmi_enter(void)
135 atomic_inc(&nmi_running);
136 /* Must have nmi_running seen before reading write flag */
138 if (mod_code_write) {
140 atomic_inc(&nmi_update_count);
144 void ftrace_nmi_exit(void)
146 /* Finish all executions before clearing nmi_running */
148 atomic_dec(&nmi_running);
151 static void wait_for_nmi(void)
153 if (!atomic_read(&nmi_running))
158 } while (atomic_read(&nmi_running));
164 do_ftrace_mod_code(unsigned long ip, void *new_code)
166 mod_code_ip = (void *)ip;
167 mod_code_newcode = new_code;
169 /* The buffers need to be visible before we let NMIs write them */
174 /* Make sure write bit is visible before we wait on NMIs */
179 /* Make sure all running NMIs have finished before we write the code */
184 /* Make sure the write happens before clearing the bit */
189 /* make sure NMIs see the cleared bit */
194 return mod_code_status;
200 static unsigned char ftrace_nop[MCOUNT_INSN_SIZE];
202 static unsigned char *ftrace_nop_replace(void)
208 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
209 unsigned char *new_code)
211 unsigned char replaced[MCOUNT_INSN_SIZE];
214 * Note: Due to modules and __init, code can
215 * disappear and change, we need to protect against faulting
216 * as well as code changing. We do this by using the
217 * probe_kernel_* functions.
219 * No real locking needed, this code is run through
220 * kstop_machine, or before SMP starts.
223 /* read the text we want to modify */
224 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
227 /* Make sure it is what we expect it to be */
228 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
231 /* replace the text with the new text */
232 if (do_ftrace_mod_code(ip, new_code))
240 int ftrace_make_nop(struct module *mod,
241 struct dyn_ftrace *rec, unsigned long addr)
243 unsigned char *new, *old;
244 unsigned long ip = rec->ip;
246 old = ftrace_call_replace(ip, addr);
247 new = ftrace_nop_replace();
249 return ftrace_modify_code(rec->ip, old, new);
252 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
254 unsigned char *new, *old;
255 unsigned long ip = rec->ip;
257 old = ftrace_nop_replace();
258 new = ftrace_call_replace(ip, addr);
260 return ftrace_modify_code(rec->ip, old, new);
263 int ftrace_update_ftrace_func(ftrace_func_t func)
265 unsigned long ip = (unsigned long)(&ftrace_call);
266 unsigned char old[MCOUNT_INSN_SIZE], *new;
269 memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
270 new = ftrace_call_replace(ip, (unsigned long)func);
271 ret = ftrace_modify_code(ip, old, new);
276 int __init ftrace_dyn_arch_init(void *data)
278 extern const unsigned char ftrace_test_p6nop[];
279 extern const unsigned char ftrace_test_nop5[];
280 extern const unsigned char ftrace_test_jmp[];
284 * There is no good nop for all x86 archs.
285 * We will default to using the P6_NOP5, but first we
286 * will test to make sure that the nop will actually
287 * work on this CPU. If it faults, we will then
288 * go to a lesser efficient 5 byte nop. If that fails
289 * we then just use a jmp as our nop. This isn't the most
290 * efficient nop, but we can not use a multi part nop
291 * since we would then risk being preempted in the middle
292 * of that nop, and if we enabled tracing then, it might
293 * cause a system crash.
295 * TODO: check the cpuid to determine the best nop.
299 "jmp ftrace_test_p6nop\n"
302 "nop\n" /* 2 byte jmp + 3 bytes */
307 ".byte 0x66,0x66,0x66,0x66,0x90\n"
309 ".section .fixup, \"ax\"\n"
311 " jmp ftrace_test_nop5\n"
315 _ASM_EXTABLE(ftrace_test_p6nop, 2b)
316 _ASM_EXTABLE(ftrace_test_nop5, 3b)
317 : "=r"(faulted) : "0" (faulted));
321 pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n");
322 memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE);
325 pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n");
326 memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE);
329 pr_info("ftrace: converting mcount calls to jmp . + 5\n");
330 memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE);
334 /* The return code is retured via data */
335 *(unsigned long *)data = 0;
341 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
343 #ifdef CONFIG_DYNAMIC_FTRACE
344 extern void ftrace_graph_call(void);
346 static int ftrace_mod_jmp(unsigned long ip,
347 int old_offset, int new_offset)
349 unsigned char code[MCOUNT_INSN_SIZE];
351 if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
354 if (code[0] != 0xe9 || old_offset != *(int *)(&code[1]))
357 *(int *)(&code[1]) = new_offset;
359 if (do_ftrace_mod_code(ip, &code))
365 int ftrace_enable_ftrace_graph_caller(void)
367 unsigned long ip = (unsigned long)(&ftrace_graph_call);
368 int old_offset, new_offset;
370 old_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);
371 new_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);
373 return ftrace_mod_jmp(ip, old_offset, new_offset);
376 int ftrace_disable_ftrace_graph_caller(void)
378 unsigned long ip = (unsigned long)(&ftrace_graph_call);
379 int old_offset, new_offset;
381 old_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);
382 new_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);
384 return ftrace_mod_jmp(ip, old_offset, new_offset);
387 #endif /* !CONFIG_DYNAMIC_FTRACE */
390 * Hook the return address and push it in the stack of return addrs
391 * in current thread info.
393 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
396 unsigned long long calltime;
398 struct ftrace_graph_ent trace;
399 unsigned long return_hooker = (unsigned long)
402 /* Nmi's are currently unsupported */
403 if (unlikely(in_nmi()))
406 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
410 * Protect against fault, even if it shouldn't
411 * happen. This tool is too much intrusive to
412 * ignore such a protection.
415 "1: " _ASM_MOV " (%[parent]), %[old]\n"
416 "2: " _ASM_MOV " %[return_hooker], (%[parent])\n"
417 " movl $0, %[faulted]\n"
420 ".section .fixup, \"ax\"\n"
421 "4: movl $1, %[faulted]\n"
428 : [old] "=r" (old), [faulted] "=r" (faulted)
429 : [parent] "r" (parent), [return_hooker] "r" (return_hooker)
433 if (unlikely(faulted)) {
439 calltime = cpu_clock(raw_smp_processor_id());
441 if (ftrace_push_return_trace(old, calltime,
442 self_addr, &trace.depth) == -EBUSY) {
447 trace.func = self_addr;
449 /* Only trace if the calling function expects to */
450 if (!ftrace_graph_entry(&trace)) {
451 current->curr_ret_stack--;
455 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */