// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
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* Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
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*
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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/uaccess.h>
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#include <linux/ftrace.h>
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#include <linux/string.h>
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#include <linux/init.h>
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#include <linux/io.h>
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#include <linux/kernel.h>
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#include <asm/ftrace.h>
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#include <asm/cacheflush.h>
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#include <asm/unistd.h>
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#include <trace/syscall.h>
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#ifdef CONFIG_DYNAMIC_FTRACE
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static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
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static unsigned char ftrace_nop[4];
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/*
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* If we're trying to nop out a call to a function, we instead
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* place a call to the address after the memory table.
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*
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* 8c011060 <a>:
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* 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
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* 8c011062: 22 4f sts.l pr,@-r15
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* 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
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* 8c011066: 2b 41 jmp @r1
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* 8c011068: 2a 40 lds r0,pr
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* 8c01106a: 09 00 nop
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* 8c01106c: 68 24 .word 0x2468 <--- ip
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* 8c01106e: 1d 8c .word 0x8c1d
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* 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
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*
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* We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
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* past the _mcount call and continue executing code like normal.
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*/
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static unsigned char *ftrace_nop_replace(unsigned long ip)
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{
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__raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
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return ftrace_nop;
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}
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static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
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{
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/* Place the address in the memory table. */
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__raw_writel(addr, ftrace_replaced_code);
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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 ftrace_replaced_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) Wait for any running NMIs to finish and set a flag that says
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* we are modifying code, it is done in an atomic operation.
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* 3) Write the code
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* 4) clear the flag.
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* 5) 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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#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
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static atomic_t nmi_running = ATOMIC_INIT(0);
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static int mod_code_status; /* holds return value of text 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 void clear_mod_flag(void)
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{
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int old = atomic_read(&nmi_running);
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for (;;) {
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int new = old & ~MOD_CODE_WRITE_FLAG;
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if (old == new)
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break;
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old = atomic_cmpxchg(&nmi_running, old, new);
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}
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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 = copy_to_kernel_nofault(mod_code_ip, mod_code_newcode,
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MCOUNT_INSN_SIZE);
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/* if we fail, then kill any new writers */
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if (mod_code_status)
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clear_mod_flag();
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}
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void arch_ftrace_nmi_enter(void)
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{
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if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
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smp_rmb();
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ftrace_mod_code();
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}
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/* Must have previous changes seen before executions */
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smp_mb();
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}
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void arch_ftrace_nmi_exit(void)
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{
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/* Finish all executions before clearing nmi_running */
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smp_mb();
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atomic_dec(&nmi_running);
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}
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static void wait_for_nmi_and_set_mod_flag(void)
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{
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if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
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return;
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do {
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cpu_relax();
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} while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
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}
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static void wait_for_nmi(void)
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{
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if (!atomic_read(&nmi_running))
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return;
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do {
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cpu_relax();
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} while (atomic_read(&nmi_running));
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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_mb();
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wait_for_nmi_and_set_mod_flag();
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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_mb();
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clear_mod_flag();
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wait_for_nmi();
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return mod_code_status;
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}
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static int 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:
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* We are paranoid about modifying text, as if a bug was to happen, it
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* could cause us to read or write to someplace that could cause harm.
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* Carefully read and modify the code with probe_kernel_*(), and make
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* sure what we read is what we expected it to be before modifying it.
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*/
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/* read the text we want to modify */
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if (copy_from_kernel_nofault(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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flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
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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) + MCOUNT_INSN_OFFSET;
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unsigned char old[MCOUNT_INSN_SIZE], *new;
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memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
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new = ftrace_call_replace(ip, (unsigned long)func);
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return ftrace_modify_code(ip, old, new);
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}
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int ftrace_make_nop(struct module *mod,
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struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned char *new, *old;
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unsigned long ip = rec->ip;
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old = ftrace_call_replace(ip, addr);
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new = ftrace_nop_replace(ip);
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return ftrace_modify_code(rec->ip, old, new);
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}
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int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned char *new, *old;
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unsigned long ip = rec->ip;
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old = ftrace_nop_replace(ip);
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new = ftrace_call_replace(ip, addr);
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return ftrace_modify_code(rec->ip, old, new);
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}
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int __init ftrace_dyn_arch_init(void)
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{
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return 0;
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}
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#endif /* CONFIG_DYNAMIC_FTRACE */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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#ifdef CONFIG_DYNAMIC_FTRACE
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extern void ftrace_graph_call(void);
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static int ftrace_mod(unsigned long ip, unsigned long old_addr,
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unsigned long new_addr)
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{
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unsigned char code[MCOUNT_INSN_SIZE];
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if (copy_from_kernel_nofault(code, (void *)ip, MCOUNT_INSN_SIZE))
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return -EFAULT;
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if (old_addr != __raw_readl((unsigned long *)code))
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return -EINVAL;
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__raw_writel(new_addr, ip);
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return 0;
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}
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int ftrace_enable_ftrace_graph_caller(void)
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{
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unsigned long ip, old_addr, new_addr;
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ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
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old_addr = (unsigned long)(&skip_trace);
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new_addr = (unsigned long)(&ftrace_graph_caller);
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return ftrace_mod(ip, old_addr, new_addr);
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}
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int ftrace_disable_ftrace_graph_caller(void)
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{
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unsigned long ip, old_addr, new_addr;
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ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
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old_addr = (unsigned long)(&ftrace_graph_caller);
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new_addr = (unsigned long)(&skip_trace);
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return ftrace_mod(ip, old_addr, new_addr);
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}
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#endif /* CONFIG_DYNAMIC_FTRACE */
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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 the current thread info.
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*
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* This is the main routine for the function graph tracer. The function
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* graph tracer essentially works like this:
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*
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* parent is the stack address containing self_addr's return address.
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* We pull the real return address out of parent and store it in
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* current's ret_stack. Then, we replace the return address on the stack
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* with the address of return_to_handler. self_addr is the function that
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* called mcount.
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*
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* When self_addr returns, it will jump to return_to_handler which calls
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* ftrace_return_to_handler. ftrace_return_to_handler will pull the real
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* return address off of current's ret_stack and jump to it.
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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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int faulted;
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unsigned long return_hooker = (unsigned long)&return_to_handler;
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if (unlikely(ftrace_graph_is_dead()))
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return;
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if (unlikely(atomic_read(¤t->tracing_graph_pause)))
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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: \n\t"
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"mov.l @%2, %0 \n\t"
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"2: \n\t"
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"mov.l %3, @%2 \n\t"
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"mov #0, %1 \n\t"
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"3: \n\t"
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".section .fixup, \"ax\" \n\t"
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"4: \n\t"
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"mov.l 5f, %0 \n\t"
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"jmp @%0 \n\t"
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" mov #1, %1 \n\t"
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".balign 4 \n\t"
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"5: .long 3b \n\t"
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".previous \n\t"
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".section __ex_table,\"a\" \n\t"
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".long 1b, 4b \n\t"
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".long 2b, 4b \n\t"
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".previous \n\t"
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: "=&r" (old), "=r" (faulted)
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: "r" (parent), "r" (return_hooker)
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);
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if (unlikely(faulted)) {
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ftrace_graph_stop();
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WARN_ON(1);
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return;
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}
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if (function_graph_enter(old, self_addr, 0, NULL))
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__raw_writel(old, parent);
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}
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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