183 lines
4.5 KiB
C
183 lines
4.5 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/init.h>
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#include <linux/list.h>
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#include <asm/ftrace.h>
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#include <asm/nops.h>
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/* Long is fine, even if it is only 4 bytes ;-) */
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static unsigned long *ftrace_nop;
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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 notrace 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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notrace unsigned char *ftrace_nop_replace(void)
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{
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return (char *)ftrace_nop;
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}
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notrace 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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notrace 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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* __copy_*_user 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 (__copy_from_user_inatomic(replaced, (char __user *)ip,
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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 (__copy_to_user_inatomic((char __user *)ip, new_code,
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MCOUNT_INSN_SIZE))
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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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notrace 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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notrace int ftrace_mcount_set(unsigned long *data)
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{
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/* mcount is initialized as a nop */
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*data = 0;
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return 0;
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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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"jmp ftrace_test_jmp\n"
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/* This code needs to stay around */
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".section .text, \"ax\"\n"
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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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"jmp 1f\n"
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".previous\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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ftrace_nop = (unsigned long *)ftrace_test_p6nop;
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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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ftrace_nop = (unsigned long *)ftrace_test_nop5;
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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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ftrace_nop = (unsigned long *)ftrace_test_jmp;
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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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