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