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