163 lines
3.6 KiB
C
163 lines
3.6 KiB
C
/*
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* Dynamic function tracing support.
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*
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* Copyright (C) 2008 Abhishek Sagar <sagar.abhishek@gmail.com>
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* Copyright (C) 2010 Rabin Vincent <rabin@rab.in>
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*
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* For licencing details, see COPYING.
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*
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* Defines low-level handling of mcount calls when the kernel
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* is compiled with the -pg flag. When using dynamic ftrace, the
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* mcount call-sites get patched with NOP till they are enabled.
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* All code mutation routines here are called under stop_machine().
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*/
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#include <linux/ftrace.h>
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#include <linux/uaccess.h>
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#include <asm/cacheflush.h>
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#include <asm/ftrace.h>
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#define NOP 0xe8bd4000 /* pop {lr} */
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#ifdef CONFIG_OLD_MCOUNT
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#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
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#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
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#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
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static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
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{
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return rec->arch.old_mcount ? OLD_NOP : NOP;
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}
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static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
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{
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if (!rec->arch.old_mcount)
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return addr;
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if (addr == MCOUNT_ADDR)
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addr = OLD_MCOUNT_ADDR;
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else if (addr == FTRACE_ADDR)
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addr = OLD_FTRACE_ADDR;
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return addr;
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}
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#else
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static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
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{
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return NOP;
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}
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static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
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{
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return addr;
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}
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#endif
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/* construct a branch (BL) instruction to addr */
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static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
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{
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long offset;
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offset = (long)addr - (long)(pc + 8);
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if (unlikely(offset < -33554432 || offset > 33554428)) {
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/* Can't generate branches that far (from ARM ARM). Ftrace
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* doesn't generate branches outside of kernel text.
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*/
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WARN_ON_ONCE(1);
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return 0;
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}
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offset = (offset >> 2) & 0x00ffffff;
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return 0xeb000000 | offset;
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}
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static int ftrace_modify_code(unsigned long pc, unsigned long old,
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unsigned long new)
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{
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unsigned long replaced;
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if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
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return -EFAULT;
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if (replaced != old)
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return -EINVAL;
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if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
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return -EPERM;
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flush_icache_range(pc, pc + 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 pc, old;
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unsigned long new;
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int ret;
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pc = (unsigned long)&ftrace_call;
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memcpy(&old, &ftrace_call, MCOUNT_INSN_SIZE);
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new = ftrace_call_replace(pc, (unsigned long)func);
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ret = ftrace_modify_code(pc, old, new);
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#ifdef CONFIG_OLD_MCOUNT
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if (!ret) {
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pc = (unsigned long)&ftrace_call_old;
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memcpy(&old, &ftrace_call_old, MCOUNT_INSN_SIZE);
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new = ftrace_call_replace(pc, (unsigned long)func);
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ret = ftrace_modify_code(pc, old, new);
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}
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#endif
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return ret;
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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 long new, old;
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unsigned long ip = rec->ip;
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old = ftrace_nop_replace(rec);
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new = ftrace_call_replace(ip, adjust_address(rec, addr));
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return ftrace_modify_code(rec->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 long ip = rec->ip;
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unsigned long old;
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unsigned long new;
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int ret;
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old = ftrace_call_replace(ip, adjust_address(rec, addr));
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new = ftrace_nop_replace(rec);
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ret = ftrace_modify_code(ip, old, new);
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#ifdef CONFIG_OLD_MCOUNT
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if (ret == -EINVAL && addr == MCOUNT_ADDR) {
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rec->arch.old_mcount = true;
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old = ftrace_call_replace(ip, adjust_address(rec, addr));
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new = ftrace_nop_replace(rec);
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ret = ftrace_modify_code(ip, old, new);
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}
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#endif
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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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*(unsigned long *)data = 0;
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return 0;
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}
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