/* * Code for replacing ftrace calls with jumps. * * Copyright (C) 2007-2008 Steven Rostedt * * Thanks goes to Ingo Molnar, for suggesting the idea. * Mathieu Desnoyers, for suggesting postponing the modifications. * Arjan van de Ven, for keeping me straight, and explaining to me * the dangers of modifying code on the run. */ #include #include #include #include #include #include #include #include #include #include #include #ifdef CONFIG_FUNCTION_RET_TRACER /* * These functions are picked from those used on * this page for dynamic ftrace. They have been * simplified to ignore all traces in NMI context. */ static atomic_t in_nmi; void ftrace_nmi_enter(void) { atomic_inc(&in_nmi); } void ftrace_nmi_exit(void) { atomic_dec(&in_nmi); } /* * Synchronize accesses to return adresses stack with * interrupts. */ static raw_spinlock_t ret_stack_lock; /* Add a function return address to the trace stack on thread info.*/ static int push_return_trace(unsigned long ret, unsigned long long time, unsigned long func) { int index; struct thread_info *ti; unsigned long flags; int err = 0; raw_local_irq_save(flags); __raw_spin_lock(&ret_stack_lock); ti = current_thread_info(); /* The return trace stack is full */ if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1) { err = -EBUSY; goto out; } index = ++ti->curr_ret_stack; ti->ret_stack[index].ret = ret; ti->ret_stack[index].func = func; ti->ret_stack[index].calltime = time; out: __raw_spin_unlock(&ret_stack_lock); raw_local_irq_restore(flags); return err; } /* Retrieve a function return address to the trace stack on thread info.*/ static void pop_return_trace(unsigned long *ret, unsigned long long *time, unsigned long *func) { struct thread_info *ti; int index; unsigned long flags; raw_local_irq_save(flags); __raw_spin_lock(&ret_stack_lock); ti = current_thread_info(); index = ti->curr_ret_stack; *ret = ti->ret_stack[index].ret; *func = ti->ret_stack[index].func; *time = ti->ret_stack[index].calltime; ti->curr_ret_stack--; __raw_spin_unlock(&ret_stack_lock); raw_local_irq_restore(flags); } /* * Send the trace to the ring-buffer. * @return the original return address. */ unsigned long ftrace_return_to_handler(void) { struct ftrace_retfunc trace; pop_return_trace(&trace.ret, &trace.calltime, &trace.func); trace.rettime = cpu_clock(raw_smp_processor_id()); ftrace_function_return(&trace); return trace.ret; } /* * Hook the return address and push it in the stack of return addrs * in current thread info. */ asmlinkage void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr) { unsigned long old; unsigned long long calltime; int faulted; unsigned long return_hooker = (unsigned long) &return_to_handler; /* Nmi's are currently unsupported */ if (atomic_read(&in_nmi)) return; /* * Protect against fault, even if it shouldn't * happen. This tool is too much intrusive to * ignore such a protection. */ asm volatile( "1: movl (%[parent_old]), %[old]\n" "2: movl %[return_hooker], (%[parent_replaced])\n" " movl $0, %[faulted]\n" ".section .fixup, \"ax\"\n" "3: movl $1, %[faulted]\n" ".previous\n" ".section __ex_table, \"a\"\n" " .long 1b, 3b\n" " .long 2b, 3b\n" ".previous\n" : [parent_replaced] "=r" (parent), [old] "=r" (old), [faulted] "=r" (faulted) : [parent_old] "0" (parent), [return_hooker] "r" (return_hooker) : "memory" ); if (WARN_ON(faulted)) { unregister_ftrace_return(); return; } if (WARN_ON(!__kernel_text_address(old))) { unregister_ftrace_return(); *parent = old; return; } calltime = cpu_clock(raw_smp_processor_id()); if (push_return_trace(old, calltime, self_addr) == -EBUSY) *parent = old; } static int __init init_ftrace_function_return(void) { ret_stack_lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; return 0; } device_initcall(init_ftrace_function_return); #endif #ifdef CONFIG_DYNAMIC_FTRACE union ftrace_code_union { char code[MCOUNT_INSN_SIZE]; struct { char e8; int offset; } __attribute__((packed)); }; static int ftrace_calc_offset(long ip, long addr) { return (int)(addr - ip); } unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) { static union ftrace_code_union calc; calc.e8 = 0xe8; calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr); /* * No locking needed, this must be called via kstop_machine * which in essence is like running on a uniprocessor machine. */ return calc.code; } /* * Modifying code must take extra care. On an SMP machine, if * the code being modified is also being executed on another CPU * that CPU will have undefined results and possibly take a GPF. * We use kstop_machine to stop other CPUS from exectuing code. * But this does not stop NMIs from happening. We still need * to protect against that. We separate out the modification of * the code to take care of this. * * Two buffers are added: An IP buffer and a "code" buffer. * * 1) Put the instruction pointer into the IP buffer * and the new code into the "code" buffer. * 2) Set a flag that says we are modifying code * 3) Wait for any running NMIs to finish. * 4) Write the code * 5) clear the flag. * 6) Wait for any running NMIs to finish. * * If an NMI is executed, the first thing it does is to call * "ftrace_nmi_enter". This will check if the flag is set to write * and if it is, it will write what is in the IP and "code" buffers. * * The trick is, it does not matter if everyone is writing the same * content to the code location. Also, if a CPU is executing code * it is OK to write to that code location if the contents being written * are the same as what exists. */ static atomic_t in_nmi = ATOMIC_INIT(0); static int mod_code_status; /* holds return value of text write */ static int mod_code_write; /* set when NMI should do the write */ static void *mod_code_ip; /* holds the IP to write to */ static void *mod_code_newcode; /* holds the text to write to the IP */ static unsigned nmi_wait_count; static atomic_t nmi_update_count = ATOMIC_INIT(0); int ftrace_arch_read_dyn_info(char *buf, int size) { int r; r = snprintf(buf, size, "%u %u", nmi_wait_count, atomic_read(&nmi_update_count)); return r; } static void ftrace_mod_code(void) { /* * Yes, more than one CPU process can be writing to mod_code_status. * (and the code itself) * But if one were to fail, then they all should, and if one were * to succeed, then they all should. */ mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode, MCOUNT_INSN_SIZE); } void ftrace_nmi_enter(void) { atomic_inc(&in_nmi); /* Must have in_nmi seen before reading write flag */ smp_mb(); if (mod_code_write) { ftrace_mod_code(); atomic_inc(&nmi_update_count); } } void ftrace_nmi_exit(void) { /* Finish all executions before clearing in_nmi */ smp_wmb(); atomic_dec(&in_nmi); } static void wait_for_nmi(void) { int waited = 0; while (atomic_read(&in_nmi)) { waited = 1; cpu_relax(); } if (waited) nmi_wait_count++; } static int do_ftrace_mod_code(unsigned long ip, void *new_code) { mod_code_ip = (void *)ip; mod_code_newcode = new_code; /* The buffers need to be visible before we let NMIs write them */ smp_wmb(); mod_code_write = 1; /* Make sure write bit is visible before we wait on NMIs */ smp_mb(); wait_for_nmi(); /* Make sure all running NMIs have finished before we write the code */ smp_mb(); ftrace_mod_code(); /* Make sure the write happens before clearing the bit */ smp_wmb(); mod_code_write = 0; /* make sure NMIs see the cleared bit */ smp_mb(); wait_for_nmi(); return mod_code_status; } static unsigned char ftrace_nop[MCOUNT_INSN_SIZE]; unsigned char *ftrace_nop_replace(void) { return ftrace_nop; } int ftrace_modify_code(unsigned long ip, unsigned char *old_code, unsigned char *new_code) { unsigned char replaced[MCOUNT_INSN_SIZE]; /* * Note: Due to modules and __init, code can * disappear and change, we need to protect against faulting * as well as code changing. We do this by using the * probe_kernel_* functions. * * No real locking needed, this code is run through * kstop_machine, or before SMP starts. */ /* read the text we want to modify */ if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE)) return -EFAULT; /* Make sure it is what we expect it to be */ if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) return -EINVAL; /* replace the text with the new text */ if (do_ftrace_mod_code(ip, new_code)) return -EPERM; sync_core(); return 0; } int ftrace_update_ftrace_func(ftrace_func_t func) { unsigned long ip = (unsigned long)(&ftrace_call); unsigned char old[MCOUNT_INSN_SIZE], *new; int ret; memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE); new = ftrace_call_replace(ip, (unsigned long)func); ret = ftrace_modify_code(ip, old, new); return ret; } int __init ftrace_dyn_arch_init(void *data) { extern const unsigned char ftrace_test_p6nop[]; extern const unsigned char ftrace_test_nop5[]; extern const unsigned char ftrace_test_jmp[]; int faulted = 0; /* * There is no good nop for all x86 archs. * We will default to using the P6_NOP5, but first we * will test to make sure that the nop will actually * work on this CPU. If it faults, we will then * go to a lesser efficient 5 byte nop. If that fails * we then just use a jmp as our nop. This isn't the most * efficient nop, but we can not use a multi part nop * since we would then risk being preempted in the middle * of that nop, and if we enabled tracing then, it might * cause a system crash. * * TODO: check the cpuid to determine the best nop. */ asm volatile ( "ftrace_test_jmp:" "jmp ftrace_test_p6nop\n" "nop\n" "nop\n" "nop\n" /* 2 byte jmp + 3 bytes */ "ftrace_test_p6nop:" P6_NOP5 "jmp 1f\n" "ftrace_test_nop5:" ".byte 0x66,0x66,0x66,0x66,0x90\n" "1:" ".section .fixup, \"ax\"\n" "2: movl $1, %0\n" " jmp ftrace_test_nop5\n" "3: movl $2, %0\n" " jmp 1b\n" ".previous\n" _ASM_EXTABLE(ftrace_test_p6nop, 2b) _ASM_EXTABLE(ftrace_test_nop5, 3b) : "=r"(faulted) : "0" (faulted)); switch (faulted) { case 0: pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n"); memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE); break; case 1: pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n"); memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE); break; case 2: pr_info("ftrace: converting mcount calls to jmp . + 5\n"); memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE); break; } /* The return code is retured via data */ *(unsigned long *)data = 0; return 0; } #endif