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ftrace.c

/*
 * ftrace graph code
 *
 * Copyright (C) 2009-2010 Analog Devices Inc.
 * Licensed under the GPL-2 or later.
 */

#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/uaccess.h>
#include <asm/atomic.h>
#include <asm/cacheflush.h>

#ifdef CONFIG_DYNAMIC_FTRACE

static const unsigned char mnop[] = {
      0x03, 0xc0, 0x00, 0x18, /* MNOP; */
      0x03, 0xc0, 0x00, 0x18, /* MNOP; */
};

static void bfin_make_pcrel24(unsigned char *insn, unsigned long src,
                              unsigned long dst)
{
      uint32_t pcrel = (dst - src) >> 1;
      insn[0] = pcrel >> 16;
      insn[1] = 0xe3;
      insn[2] = pcrel;
      insn[3] = pcrel >> 8;
}
#define bfin_make_pcrel24(insn, src, dst) bfin_make_pcrel24(insn, src, (unsigned long)(dst))

static int ftrace_modify_code(unsigned long ip, const unsigned char *code,
                              unsigned long len)
{
      int ret = probe_kernel_write((void *)ip, (void *)code, len);
      flush_icache_range(ip, ip + len);
      return ret;
}

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
                    unsigned long addr)
{
      /* Turn the mcount call site into two MNOPs as those are 32bit insns */
      return ftrace_modify_code(rec->ip, mnop, sizeof(mnop));
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
      /* Restore the mcount call site */
      unsigned char call[8];
      call[0] = 0x67; /* [--SP] = RETS; */
      call[1] = 0x01;
      bfin_make_pcrel24(&call[2], rec->ip + 2, addr);
      call[6] = 0x27; /* RETS = [SP++]; */
      call[7] = 0x01;
      return ftrace_modify_code(rec->ip, call, sizeof(call));
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
      unsigned char call[4];
      unsigned long ip = (unsigned long)&ftrace_call;
      bfin_make_pcrel24(call, ip, func);
      return ftrace_modify_code(ip, call, sizeof(call));
}

int __init ftrace_dyn_arch_init(void *data)
{
      /* return value is done indirectly via data */
      *(unsigned long *)data = 0;

      return 0;
}

#endif

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

# ifdef CONFIG_DYNAMIC_FTRACE

extern void ftrace_graph_call(void);

int ftrace_enable_ftrace_graph_caller(void)
{
      unsigned long ip = (unsigned long)&ftrace_graph_call;
      uint16_t jump_pcrel12 = ((unsigned long)&ftrace_graph_caller - ip) >> 1;
      jump_pcrel12 |= 0x2000;
      return ftrace_modify_code(ip, (void *)&jump_pcrel12, sizeof(jump_pcrel12));
}

int ftrace_disable_ftrace_graph_caller(void)
{
      return ftrace_modify_code((unsigned long)&ftrace_graph_call, empty_zero_page, 2);
}

# endif

/*
 * Hook the return address and push it in the stack of return addrs
 * in current thread info.
 */
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
                           unsigned long frame_pointer)
{
      struct ftrace_graph_ent trace;
      unsigned long return_hooker = (unsigned long)&return_to_handler;

      if (unlikely(atomic_read(&current->tracing_graph_pause)))
            return;

      if (ftrace_push_return_trace(*parent, self_addr, &trace.depth,
                                   frame_pointer) == -EBUSY)
            return;

      trace.func = self_addr;

      /* Only trace if the calling function expects to */
      if (!ftrace_graph_entry(&trace)) {
            current->curr_ret_stack--;
            return;
      }

      /* all is well in the world !  hijack RETS ... */
      *parent = return_hooker;
}

#endif

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