old-cross-binutils/gdb/record-btrace.c

/* Branch trace support for GDB, the GNU debugger.

   Copyright (C) 2013-2014 Free Software Foundation, Inc.

   Contributed by Intel Corp. <markus.t.metzger@intel.com>

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "record.h"
#include "gdbthread.h"
#include "target.h"
#include "gdbcmd.h"
#include "disasm.h"
#include "observer.h"
#include "exceptions.h"
#include "cli/cli-utils.h"
#include "source.h"
#include "ui-out.h"
#include "symtab.h"
#include "filenames.h"
#include "regcache.h"
#include "frame-unwind.h"
#include "hashtab.h"

/* The target_ops of record-btrace.  */
static struct target_ops record_btrace_ops;

/* A new thread observer enabling branch tracing for the new thread.  */
static struct observer *record_btrace_thread_observer;

/* Temporarily allow memory accesses.  */
static int record_btrace_allow_memory_access;

/* Print a record-btrace debug message.  Use do ... while (0) to avoid
   ambiguities when used in if statements.  */

#define DEBUG(msg, args...)						\
  do									\
    {									\
      if (record_debug != 0)						\
        fprintf_unfiltered (gdb_stdlog,					\
			    "[record-btrace] " msg "\n", ##args);	\
    }									\
  while (0)


/* Update the branch trace for the current thread and return a pointer to its
   thread_info.

   Throws an error if there is no thread or no trace.  This function never
   returns NULL.  */

static struct thread_info *
require_btrace_thread (void)
{
  struct thread_info *tp;
  struct btrace_thread_info *btinfo;

  DEBUG ("require");

  tp = find_thread_ptid (inferior_ptid);
  if (tp == NULL)
    error (_("No thread."));

  btrace_fetch (tp);

  btinfo = &tp->btrace;

  if (btinfo->begin == NULL)
    error (_("No trace."));

  return tp;
}

/* Update the branch trace for the current thread and return a pointer to its
   branch trace information struct.

   Throws an error if there is no thread or no trace.  This function never
   returns NULL.  */

static struct btrace_thread_info *
require_btrace (void)
{
  struct thread_info *tp;

  tp = require_btrace_thread ();

  return &tp->btrace;
}

/* Enable branch tracing for one thread.  Warn on errors.  */

static void
record_btrace_enable_warn (struct thread_info *tp)
{
  volatile struct gdb_exception error;

  TRY_CATCH (error, RETURN_MASK_ERROR)
    btrace_enable (tp);

  if (error.message != NULL)
    warning ("%s", error.message);
}

/* Callback function to disable branch tracing for one thread.  */

static void
record_btrace_disable_callback (void *arg)
{
  struct thread_info *tp;

  tp = arg;

  btrace_disable (tp);
}

/* Enable automatic tracing of new threads.  */

static void
record_btrace_auto_enable (void)
{
  DEBUG ("attach thread observer");

  record_btrace_thread_observer
    = observer_attach_new_thread (record_btrace_enable_warn);
}

/* Disable automatic tracing of new threads.  */

static void
record_btrace_auto_disable (void)
{
  /* The observer may have been detached, already.  */
  if (record_btrace_thread_observer == NULL)
    return;

  DEBUG ("detach thread observer");

  observer_detach_new_thread (record_btrace_thread_observer);
  record_btrace_thread_observer = NULL;
}

/* The to_open method of target record-btrace.  */

static void
record_btrace_open (char *args, int from_tty)
{
  struct cleanup *disable_chain;
  struct thread_info *tp;

  DEBUG ("open");

  record_preopen ();

  if (!target_has_execution)
    error (_("The program is not being run."));

  if (!target_supports_btrace ())
    error (_("Target does not support branch tracing."));

  gdb_assert (record_btrace_thread_observer == NULL);

  disable_chain = make_cleanup (null_cleanup, NULL);
  ALL_THREADS (tp)
    if (args == NULL || *args == 0 || number_is_in_list (args, tp->num))
      {
	btrace_enable (tp);

	make_cleanup (record_btrace_disable_callback, tp);
      }

  record_btrace_auto_enable ();

  push_target (&record_btrace_ops);

  observer_notify_record_changed (current_inferior (),  1);

  discard_cleanups (disable_chain);
}

/* The to_stop_recording method of target record-btrace.  */

static void
record_btrace_stop_recording (void)
{
  struct thread_info *tp;

  DEBUG ("stop recording");

  record_btrace_auto_disable ();

  ALL_THREADS (tp)
    if (tp->btrace.target != NULL)
      btrace_disable (tp);
}

/* The to_close method of target record-btrace.  */

static void
record_btrace_close (void)
{
  /* Make sure automatic recording gets disabled even if we did not stop
     recording before closing the record-btrace target.  */
  record_btrace_auto_disable ();

  /* We already stopped recording.  */
}

/* The to_info_record method of target record-btrace.  */

static void
record_btrace_info (void)
{
  struct btrace_thread_info *btinfo;
  struct thread_info *tp;
  unsigned int insns, calls;

  DEBUG ("info");

  tp = find_thread_ptid (inferior_ptid);
  if (tp == NULL)
    error (_("No thread."));

  btrace_fetch (tp);

  insns = 0;
  calls = 0;

  btinfo = &tp->btrace;
  if (btinfo->begin != NULL)
    {
      struct btrace_call_iterator call;
      struct btrace_insn_iterator insn;

      btrace_call_end (&call, btinfo);
      btrace_call_prev (&call, 1);
      calls = btrace_call_number (&call);

      btrace_insn_end (&insn, btinfo);
      btrace_insn_prev (&insn, 1);
      insns = btrace_insn_number (&insn);
    }

  printf_unfiltered (_("Recorded %u instructions in %u functions for thread "
		       "%d (%s).\n"), insns, calls, tp->num,
		     target_pid_to_str (tp->ptid));

  if (btrace_is_replaying (tp))
    printf_unfiltered (_("Replay in progress.  At instruction %u.\n"),
		       btrace_insn_number (btinfo->replay));
}

/* Print an unsigned int.  */

static void
ui_out_field_uint (struct ui_out *uiout, const char *fld, unsigned int val)
{
  ui_out_field_fmt (uiout, fld, "%u", val);
}

/* Disassemble a section of the recorded instruction trace.  */

static void
btrace_insn_history (struct ui_out *uiout,
		     const struct btrace_insn_iterator *begin,
		     const struct btrace_insn_iterator *end, int flags)
{
  struct gdbarch *gdbarch;
  struct btrace_insn_iterator it;

  DEBUG ("itrace (0x%x): [%u; %u)", flags, btrace_insn_number (begin),
	 btrace_insn_number (end));

  gdbarch = target_gdbarch ();

  for (it = *begin; btrace_insn_cmp (&it, end) != 0; btrace_insn_next (&it, 1))
    {
      const struct btrace_insn *insn;

      insn = btrace_insn_get (&it);

      /* Print the instruction index.  */
      ui_out_field_uint (uiout, "index", btrace_insn_number (&it));
      ui_out_text (uiout, "\t");

      /* Disassembly with '/m' flag may not produce the expected result.
	 See PR gdb/11833.  */
      gdb_disassembly (gdbarch, uiout, NULL, flags, 1, insn->pc, insn->pc + 1);
    }
}

/* The to_insn_history method of target record-btrace.  */

static void
record_btrace_insn_history (int size, int flags)
{
  struct btrace_thread_info *btinfo;
  struct btrace_insn_history *history;
  struct btrace_insn_iterator begin, end;
  struct cleanup *uiout_cleanup;
  struct ui_out *uiout;
  unsigned int context, covered;

  uiout = current_uiout;
  uiout_cleanup = make_cleanup_ui_out_tuple_begin_end (uiout,
						       "insn history");
  context = abs (size);
  if (context == 0)
    error (_("Bad record instruction-history-size."));

  btinfo = require_btrace ();
  history = btinfo->insn_history;
  if (history == NULL)
    {
      struct btrace_insn_iterator *replay;

      DEBUG ("insn-history (0x%x): %d", flags, size);

      /* If we're replaying, we start at the replay position.  Otherwise, we
	 start at the tail of the trace.  */
      replay = btinfo->replay;
      if (replay != NULL)
	begin = *replay;
      else
	btrace_insn_end (&begin, btinfo);

      /* We start from here and expand in the requested direction.  Then we
	 expand in the other direction, as well, to fill up any remaining
	 context.  */
      end = begin;
      if (size < 0)
	{
	  /* We want the current position covered, as well.  */
	  covered = btrace_insn_next (&end, 1);
	  covered += btrace_insn_prev (&begin, context - covered);
	  covered += btrace_insn_next (&end, context - covered);
	}
      else
	{
	  covered = btrace_insn_next (&end, context);
	  covered += btrace_insn_prev (&begin, context - covered);
	}
    }
  else
    {
      begin = history->begin;
      end = history->end;

      DEBUG ("insn-history (0x%x): %d, prev: [%u; %u)", flags, size,
	     btrace_insn_number (&begin), btrace_insn_number (&end));

      if (size < 0)
	{
	  end = begin;
	  covered = btrace_insn_prev (&begin, context);
	}
      else
	{
	  begin = end;
	  covered = btrace_insn_next (&end, context);
	}
    }

  if (covered > 0)
    btrace_insn_history (uiout, &begin, &end, flags);
  else
    {
      if (size < 0)
	printf_unfiltered (_("At the start of the branch trace record.\n"));
      else
	printf_unfiltered (_("At the end of the branch trace record.\n"));
    }

  btrace_set_insn_history (btinfo, &begin, &end);
  do_cleanups (uiout_cleanup);
}

/* The to_insn_history_range method of target record-btrace.  */

static void
record_btrace_insn_history_range (ULONGEST from, ULONGEST to, int flags)
{
  struct btrace_thread_info *btinfo;
  struct btrace_insn_history *history;
  struct btrace_insn_iterator begin, end;
  struct cleanup *uiout_cleanup;
  struct ui_out *uiout;
  unsigned int low, high;
  int found;

  uiout = current_uiout;
  uiout_cleanup = make_cleanup_ui_out_tuple_begin_end (uiout,
						       "insn history");
  low = from;
  high = to;

  DEBUG ("insn-history (0x%x): [%u; %u)", flags, low, high);

  /* Check for wrap-arounds.  */
  if (low != from || high != to)
    error (_("Bad range."));

  if (high < low)
    error (_("Bad range."));

  btinfo = require_btrace ();

  found = btrace_find_insn_by_number (&begin, btinfo, low);
  if (found == 0)
    error (_("Range out of bounds."));

  found = btrace_find_insn_by_number (&end, btinfo, high);
  if (found == 0)
    {
      /* Silently truncate the range.  */
      btrace_insn_end (&end, btinfo);
    }
  else
    {
      /* We want both begin and end to be inclusive.  */
      btrace_insn_next (&end, 1);
    }

  btrace_insn_history (uiout, &begin, &end, flags);
  btrace_set_insn_history (btinfo, &begin, &end);

  do_cleanups (uiout_cleanup);
}

/* The to_insn_history_from method of target record-btrace.  */

static void
record_btrace_insn_history_from (ULONGEST from, int size, int flags)
{
  ULONGEST begin, end, context;

  context = abs (size);
  if (context == 0)
    error (_("Bad record instruction-history-size."));

  if (size < 0)
    {
      end = from;

      if (from < context)
	begin = 0;
      else
	begin = from - context + 1;
    }
  else
    {
      begin = from;
      end = from + context - 1;

      /* Check for wrap-around.  */
      if (end < begin)
	end = ULONGEST_MAX;
    }

  record_btrace_insn_history_range (begin, end, flags);
}

/* Print the instruction number range for a function call history line.  */

static void
btrace_call_history_insn_range (struct ui_out *uiout,
				const struct btrace_function *bfun)
{
  unsigned int begin, end, size;

  size = VEC_length (btrace_insn_s, bfun->insn);
  gdb_assert (size > 0);

  begin = bfun->insn_offset;
  end = begin + size - 1;

  ui_out_field_uint (uiout, "insn begin", begin);
  ui_out_text (uiout, ",");
  ui_out_field_uint (uiout, "insn end", end);
}

/* Print the source line information for a function call history line.  */

static void
btrace_call_history_src_line (struct ui_out *uiout,
			      const struct btrace_function *bfun)
{
  struct symbol *sym;
  int begin, end;

  sym = bfun->sym;
  if (sym == NULL)
    return;

  ui_out_field_string (uiout, "file",
		       symtab_to_filename_for_display (sym->symtab));

  begin = bfun->lbegin;
  end = bfun->lend;

  if (end < begin)
    return;

  ui_out_text (uiout, ":");
  ui_out_field_int (uiout, "min line", begin);

  if (end == begin)
    return;

  ui_out_text (uiout, ",");
  ui_out_field_int (uiout, "max line", end);
}

/* Get the name of a branch trace function.  */

static const char *
btrace_get_bfun_name (const struct btrace_function *bfun)
{
  struct minimal_symbol *msym;
  struct symbol *sym;

  if (bfun == NULL)
    return "??";

  msym = bfun->msym;
  sym = bfun->sym;

  if (sym != NULL)
    return SYMBOL_PRINT_NAME (sym);
  else if (msym != NULL)
    return SYMBOL_PRINT_NAME (msym);
  else
    return "??";
}

/* Disassemble a section of the recorded function trace.  */

static void
btrace_call_history (struct ui_out *uiout,
		     const struct btrace_thread_info *btinfo,
		     const struct btrace_call_iterator *begin,
		     const struct btrace_call_iterator *end,
		     enum record_print_flag flags)
{
  struct btrace_call_iterator it;

  DEBUG ("ftrace (0x%x): [%u; %u)", flags, btrace_call_number (begin),
	 btrace_call_number (end));

  for (it = *begin; btrace_call_cmp (&it, end) < 0; btrace_call_next (&it, 1))
    {
      const struct btrace_function *bfun;
      struct minimal_symbol *msym;
      struct symbol *sym;

      bfun = btrace_call_get (&it);
      sym = bfun->sym;
      msym = bfun->msym;

      /* Print the function index.  */
      ui_out_field_uint (uiout, "index", bfun->number);
      ui_out_text (uiout, "\t");

      if ((flags & RECORD_PRINT_INDENT_CALLS) != 0)
	{
	  int level = bfun->level + btinfo->level, i;

	  for (i = 0; i < level; ++i)
	    ui_out_text (uiout, "  ");
	}

      if (sym != NULL)
	ui_out_field_string (uiout, "function", SYMBOL_PRINT_NAME (sym));
      else if (msym != NULL)
	ui_out_field_string (uiout, "function", SYMBOL_PRINT_NAME (msym));
      else if (!ui_out_is_mi_like_p (uiout))
	ui_out_field_string (uiout, "function", "??");

      if ((flags & RECORD_PRINT_INSN_RANGE) != 0)
	{
	  ui_out_text (uiout, _("\tinst "));
	  btrace_call_history_insn_range (uiout, bfun);
	}

      if ((flags & RECORD_PRINT_SRC_LINE) != 0)
	{
	  ui_out_text (uiout, _("\tat "));
	  btrace_call_history_src_line (uiout, bfun);
	}

      ui_out_text (uiout, "\n");
    }
}

/* The to_call_history method of target record-btrace.  */

static void
record_btrace_call_history (int size, int flags)
{
  struct btrace_thread_info *btinfo;
  struct btrace_call_history *history;
  struct btrace_call_iterator begin, end;
  struct cleanup *uiout_cleanup;
  struct ui_out *uiout;
  unsigned int context, covered;

  uiout = current_uiout;
  uiout_cleanup = make_cleanup_ui_out_tuple_begin_end (uiout,
						       "insn history");
  context = abs (size);
  if (context == 0)
    error (_("Bad record function-call-history-size."));

  btinfo = require_btrace ();
  history = btinfo->call_history;
  if (history == NULL)
    {
      struct btrace_insn_iterator *replay;

      DEBUG ("call-history (0x%x): %d", flags, size);

      /* If we're replaying, we start at the replay position.  Otherwise, we
	 start at the tail of the trace.  */
      replay = btinfo->replay;
      if (replay != NULL)
	{
	  begin.function = replay->function;
	  begin.btinfo = btinfo;
	}
      else
	btrace_call_end (&begin, btinfo);

      /* We start from here and expand in the requested direction.  Then we
	 expand in the other direction, as well, to fill up any remaining
	 context.  */
      end = begin;
      if (size < 0)
	{
	  /* We want the current position covered, as well.  */
	  covered = btrace_call_next (&end, 1);
	  covered += btrace_call_prev (&begin, context - covered);
	  covered += btrace_call_next (&end, context - covered);
	}
      else
	{
	  covered = btrace_call_next (&end, context);
	  covered += btrace_call_prev (&begin, context- covered);
	}
    }
  else
    {
      begin = history->begin;
      end = history->end;

      DEBUG ("call-history (0x%x): %d, prev: [%u; %u)", flags, size,
	     btrace_call_number (&begin), btrace_call_number (&end));

      if (size < 0)
	{
	  end = begin;
	  covered = btrace_call_prev (&begin, context);
	}
      else
	{
	  begin = end;
	  covered = btrace_call_next (&end, context);
	}
    }

  if (covered > 0)
    btrace_call_history (uiout, btinfo, &begin, &end, flags);
  else
    {
      if (size < 0)
	printf_unfiltered (_("At the start of the branch trace record.\n"));
      else
	printf_unfiltered (_("At the end of the branch trace record.\n"));
    }

  btrace_set_call_history (btinfo, &begin, &end);
  do_cleanups (uiout_cleanup);
}

/* The to_call_history_range method of target record-btrace.  */

static void
record_btrace_call_history_range (ULONGEST from, ULONGEST to, int flags)
{
  struct btrace_thread_info *btinfo;
  struct btrace_call_history *history;
  struct btrace_call_iterator begin, end;
  struct cleanup *uiout_cleanup;
  struct ui_out *uiout;
  unsigned int low, high;
  int found;

  uiout = current_uiout;
  uiout_cleanup = make_cleanup_ui_out_tuple_begin_end (uiout,
						       "func history");
  low = from;
  high = to;

  DEBUG ("call-history (0x%x): [%u; %u)", flags, low, high);

  /* Check for wrap-arounds.  */
  if (low != from || high != to)
    error (_("Bad range."));

  if (high < low)
    error (_("Bad range."));

  btinfo = require_btrace ();

  found = btrace_find_call_by_number (&begin, btinfo, low);
  if (found == 0)
    error (_("Range out of bounds."));

  found = btrace_find_call_by_number (&end, btinfo, high);
  if (found == 0)
    {
      /* Silently truncate the range.  */
      btrace_call_end (&end, btinfo);
    }
  else
    {
      /* We want both begin and end to be inclusive.  */
      btrace_call_next (&end, 1);
    }

  btrace_call_history (uiout, btinfo, &begin, &end, flags);
  btrace_set_call_history (btinfo, &begin, &end);

  do_cleanups (uiout_cleanup);
}

/* The to_call_history_from method of target record-btrace.  */

static void
record_btrace_call_history_from (ULONGEST from, int size, int flags)
{
  ULONGEST begin, end, context;

  context = abs (size);
  if (context == 0)
    error (_("Bad record function-call-history-size."));

  if (size < 0)
    {
      end = from;

      if (from < context)
	begin = 0;
      else
	begin = from - context + 1;
    }
  else
    {
      begin = from;
      end = from + context - 1;

      /* Check for wrap-around.  */
      if (end < begin)
	end = ULONGEST_MAX;
    }

  record_btrace_call_history_range (begin, end, flags);
}

/* The to_record_is_replaying method of target record-btrace.  */

static int
record_btrace_is_replaying (void)
{
  struct thread_info *tp;

  ALL_THREADS (tp)
    if (btrace_is_replaying (tp))
      return 1;

  return 0;
}

/* The to_xfer_partial method of target record-btrace.  */

static LONGEST
record_btrace_xfer_partial (struct target_ops *ops, enum target_object object,
			    const char *annex, gdb_byte *readbuf,
			    const gdb_byte *writebuf, ULONGEST offset,
			    ULONGEST len)
{
  struct target_ops *t;

  /* Filter out requests that don't make sense during replay.  */
  if (!record_btrace_allow_memory_access && record_btrace_is_replaying ())
    {
      switch (object)
	{
	case TARGET_OBJECT_MEMORY:
	  {
	    struct target_section *section;

	    /* We do not allow writing memory in general.  */
	    if (writebuf != NULL)
	      return TARGET_XFER_E_UNAVAILABLE;

	    /* We allow reading readonly memory.  */
	    section = target_section_by_addr (ops, offset);
	    if (section != NULL)
	      {
		/* Check if the section we found is readonly.  */
		if ((bfd_get_section_flags (section->the_bfd_section->owner,
					    section->the_bfd_section)
		     & SEC_READONLY) != 0)
		  {
		    /* Truncate the request to fit into this section.  */
		    len = min (len, section->endaddr - offset);
		    break;
		  }
	      }

	    return TARGET_XFER_E_UNAVAILABLE;
	  }
	}
    }

  /* Forward the request.  */
  for (ops = ops->beneath; ops != NULL; ops = ops->beneath)
    if (ops->to_xfer_partial != NULL)
      return ops->to_xfer_partial (ops, object, annex, readbuf, writebuf,
				   offset, len);

  return TARGET_XFER_E_UNAVAILABLE;
}

/* The to_insert_breakpoint method of target record-btrace.  */

static int
record_btrace_insert_breakpoint (struct target_ops *ops,
				 struct gdbarch *gdbarch,
				 struct bp_target_info *bp_tgt)
{
  volatile struct gdb_exception except;
  int old, ret;

  /* Inserting breakpoints requires accessing memory.  Allow it for the
     duration of this function.  */
  old = record_btrace_allow_memory_access;
  record_btrace_allow_memory_access = 1;

  ret = 0;
  TRY_CATCH (except, RETURN_MASK_ALL)
    ret = forward_target_insert_breakpoint (ops->beneath, gdbarch, bp_tgt);

  record_btrace_allow_memory_access = old;

  if (except.reason < 0)
    throw_exception (except);

  return ret;
}

/* The to_remove_breakpoint method of target record-btrace.  */

static int
record_btrace_remove_breakpoint (struct target_ops *ops,
				 struct gdbarch *gdbarch,
				 struct bp_target_info *bp_tgt)
{
  volatile struct gdb_exception except;
  int old, ret;

  /* Removing breakpoints requires accessing memory.  Allow it for the
     duration of this function.  */
  old = record_btrace_allow_memory_access;
  record_btrace_allow_memory_access = 1;

  ret = 0;
  TRY_CATCH (except, RETURN_MASK_ALL)
    ret = forward_target_remove_breakpoint (ops->beneath, gdbarch, bp_tgt);

  record_btrace_allow_memory_access = old;

  if (except.reason < 0)
    throw_exception (except);

  return ret;
}

/* The to_fetch_registers method of target record-btrace.  */

static void
record_btrace_fetch_registers (struct target_ops *ops,
			       struct regcache *regcache, int regno)
{
  struct btrace_insn_iterator *replay;
  struct thread_info *tp;

  tp = find_thread_ptid (inferior_ptid);
  gdb_assert (tp != NULL);

  replay = tp->btrace.replay;
  if (replay != NULL)
    {
      const struct btrace_insn *insn;
      struct gdbarch *gdbarch;
      int pcreg;

      gdbarch = get_regcache_arch (regcache);
      pcreg = gdbarch_pc_regnum (gdbarch);
      if (pcreg < 0)
	return;

      /* We can only provide the PC register.  */
      if (regno >= 0 && regno != pcreg)
	return;

      insn = btrace_insn_get (replay);
      gdb_assert (insn != NULL);

      regcache_raw_supply (regcache, regno, &insn->pc);
    }
  else
    {
      struct target_ops *t;

      for (t = ops->beneath; t != NULL; t = t->beneath)
	if (t->to_fetch_registers != NULL)
	  {
	    t->to_fetch_registers (t, regcache, regno);
	    break;
	  }
    }
}

/* The to_store_registers method of target record-btrace.  */

static void
record_btrace_store_registers (struct target_ops *ops,
			       struct regcache *regcache, int regno)
{
  struct target_ops *t;

  if (record_btrace_is_replaying ())
    error (_("This record target does not allow writing registers."));

  gdb_assert (may_write_registers != 0);

  for (t = ops->beneath; t != NULL; t = t->beneath)
    if (t->to_store_registers != NULL)
      {
	t->to_store_registers (t, regcache, regno);
	return;
      }

  noprocess ();
}

/* The to_prepare_to_store method of target record-btrace.  */

static void
record_btrace_prepare_to_store (struct target_ops *ops,
				struct regcache *regcache)
{
  struct target_ops *t;

  if (record_btrace_is_replaying ())
    return;

  for (t = ops->beneath; t != NULL; t = t->beneath)
    if (t->to_prepare_to_store != NULL)
      {
	t->to_prepare_to_store (t, regcache);
	return;
      }
}

/* The branch trace frame cache.  */

struct btrace_frame_cache
{
  /* The thread.  */
  struct thread_info *tp;

  /* The frame info.  */
  struct frame_info *frame;

  /* The branch trace function segment.  */
  const struct btrace_function *bfun;
};

/* A struct btrace_frame_cache hash table indexed by NEXT.  */

static htab_t bfcache;

/* hash_f for htab_create_alloc of bfcache.  */

static hashval_t
bfcache_hash (const void *arg)
{
  const struct btrace_frame_cache *cache = arg;

  return htab_hash_pointer (cache->frame);
}

/* eq_f for htab_create_alloc of bfcache.  */

static int
bfcache_eq (const void *arg1, const void *arg2)
{
  const struct btrace_frame_cache *cache1 = arg1;
  const struct btrace_frame_cache *cache2 = arg2;

  return cache1->frame == cache2->frame;
}

/* Create a new btrace frame cache.  */

static struct btrace_frame_cache *
bfcache_new (struct frame_info *frame)
{
  struct btrace_frame_cache *cache;
  void **slot;

  cache = FRAME_OBSTACK_ZALLOC (struct btrace_frame_cache);
  cache->frame = frame;

  slot = htab_find_slot (bfcache, cache, INSERT);
  gdb_assert (*slot == NULL);
  *slot = cache;

  return cache;
}

/* Extract the branch trace function from a branch trace frame.  */

static const struct btrace_function *
btrace_get_frame_function (struct frame_info *frame)
{
  const struct btrace_frame_cache *cache;
  const struct btrace_function *bfun;
  struct btrace_frame_cache pattern;
  void **slot;

  pattern.frame = frame;

  slot = htab_find_slot (bfcache, &pattern, NO_INSERT);
  if (slot == NULL)
    return NULL;

  cache = *slot;
  return cache->bfun;
}

/* Implement stop_reason method for record_btrace_frame_unwind.  */

static enum unwind_stop_reason
record_btrace_frame_unwind_stop_reason (struct frame_info *this_frame,
					void **this_cache)
{
  const struct btrace_frame_cache *cache;
  const struct btrace_function *bfun;

  cache = *this_cache;
  bfun = cache->bfun;
  gdb_assert (bfun != NULL);

  if (bfun->up == NULL)
    return UNWIND_UNAVAILABLE;

  return UNWIND_NO_REASON;
}

/* Implement this_id method for record_btrace_frame_unwind.  */

static void
record_btrace_frame_this_id (struct frame_info *this_frame, void **this_cache,
			     struct frame_id *this_id)
{
  const struct btrace_frame_cache *cache;
  const struct btrace_function *bfun;
  CORE_ADDR code, special;

  cache = *this_cache;

  bfun = cache->bfun;
  gdb_assert (bfun != NULL);

  while (bfun->segment.prev != NULL)
    bfun = bfun->segment.prev;

  code = get_frame_func (this_frame);
  special = bfun->number;

  *this_id = frame_id_build_unavailable_stack_special (code, special);

  DEBUG ("[frame] %s id: (!stack, pc=%s, special=%s)",
	 btrace_get_bfun_name (cache->bfun),
	 core_addr_to_string_nz (this_id->code_addr),
	 core_addr_to_string_nz (this_id->special_addr));
}

/* Implement prev_register method for record_btrace_frame_unwind.  */

static struct value *
record_btrace_frame_prev_register (struct frame_info *this_frame,
				   void **this_cache,
				   int regnum)
{
  const struct btrace_frame_cache *cache;
  const struct btrace_function *bfun, *caller;
  const struct btrace_insn *insn;
  struct gdbarch *gdbarch;
  CORE_ADDR pc;
  int pcreg;

  gdbarch = get_frame_arch (this_frame);
  pcreg = gdbarch_pc_regnum (gdbarch);
  if (pcreg < 0 || regnum != pcreg)
    throw_error (NOT_AVAILABLE_ERROR,
		 _("Registers are not available in btrace record history"));

  cache = *this_cache;
  bfun = cache->bfun;
  gdb_assert (bfun != NULL);

  caller = bfun->up;
  if (caller == NULL)
    throw_error (NOT_AVAILABLE_ERROR,
		 _("No caller in btrace record history"));

  if ((bfun->flags & BFUN_UP_LINKS_TO_RET) != 0)
    {
      insn = VEC_index (btrace_insn_s, caller->insn, 0);
      pc = insn->pc;
    }
  else
    {
      insn = VEC_last (btrace_insn_s, caller->insn);
      pc = insn->pc;

      pc += gdb_insn_length (gdbarch, pc);
    }

  DEBUG ("[frame] unwound PC in %s on level %d: %s",
	 btrace_get_bfun_name (bfun), bfun->level,
	 core_addr_to_string_nz (pc));

  return frame_unwind_got_address (this_frame, regnum, pc);
}

/* Implement sniffer method for record_btrace_frame_unwind.  */

static int
record_btrace_frame_sniffer (const struct frame_unwind *self,
			     struct frame_info *this_frame,
			     void **this_cache)
{
  const struct btrace_function *bfun;
  struct btrace_frame_cache *cache;
  struct thread_info *tp;
  struct frame_info *next;

  /* THIS_FRAME does not contain a reference to its thread.  */
  tp = find_thread_ptid (inferior_ptid);
  gdb_assert (tp != NULL);

  bfun = NULL;
  next = get_next_frame (this_frame);
  if (next == NULL)
    {
      const struct btrace_insn_iterator *replay;

      replay = tp->btrace.replay;
      if (replay != NULL)
	bfun = replay->function;
    }
  else
    {
      const struct btrace_function *callee;

      callee = btrace_get_frame_function (next);
      if (callee != NULL && (callee->flags & BFUN_UP_LINKS_TO_TAILCALL) == 0)
	bfun = callee->up;
    }

  if (bfun == NULL)
    return 0;

  DEBUG ("[frame] sniffed frame for %s on level %d",
	 btrace_get_bfun_name (bfun), bfun->level);

  /* This is our frame.  Initialize the frame cache.  */
  cache = bfcache_new (this_frame);
  cache->tp = tp;
  cache->bfun = bfun;

  *this_cache = cache;
  return 1;
}

/* Implement sniffer method for record_btrace_tailcall_frame_unwind.  */

static int
record_btrace_tailcall_frame_sniffer (const struct frame_unwind *self,
				      struct frame_info *this_frame,
				      void **this_cache)
{
  const struct btrace_function *bfun, *callee;
  struct btrace_frame_cache *cache;
  struct frame_info *next;

  next = get_next_frame (this_frame);
  if (next == NULL)
    return 0;

  callee = btrace_get_frame_function (next);
  if (callee == NULL)
    return 0;

  if ((callee->flags & BFUN_UP_LINKS_TO_TAILCALL) == 0)
    return 0;

  bfun = callee->up;
  if (bfun == NULL)
    return 0;

  DEBUG ("[frame] sniffed tailcall frame for %s on level %d",
	 btrace_get_bfun_name (bfun), bfun->level);

  /* This is our frame.  Initialize the frame cache.  */
  cache = bfcache_new (this_frame);
  cache->tp = find_thread_ptid (inferior_ptid);
  cache->bfun = bfun;

  *this_cache = cache;
  return 1;
}

static void
record_btrace_frame_dealloc_cache (struct frame_info *self, void *this_cache)
{
  struct btrace_frame_cache *cache;
  void **slot;

  cache = this_cache;

  slot = htab_find_slot (bfcache, cache, NO_INSERT);
  gdb_assert (slot != NULL);

  htab_remove_elt (bfcache, cache);
}

/* btrace recording does not store previous memory content, neither the stack
   frames content.  Any unwinding would return errorneous results as the stack
   contents no longer matches the changed PC value restored from history.
   Therefore this unwinder reports any possibly unwound registers as
   <unavailable>.  */

const struct frame_unwind record_btrace_frame_unwind =
{
  NORMAL_FRAME,
  record_btrace_frame_unwind_stop_reason,
  record_btrace_frame_this_id,
  record_btrace_frame_prev_register,
  NULL,
  record_btrace_frame_sniffer,
  record_btrace_frame_dealloc_cache
};

const struct frame_unwind record_btrace_tailcall_frame_unwind =
{
  TAILCALL_FRAME,
  record_btrace_frame_unwind_stop_reason,
  record_btrace_frame_this_id,
  record_btrace_frame_prev_register,
  NULL,
  record_btrace_tailcall_frame_sniffer,
  record_btrace_frame_dealloc_cache
};

/* The to_resume method of target record-btrace.  */

static void
record_btrace_resume (struct target_ops *ops, ptid_t ptid, int step,
		      enum gdb_signal signal)
{
  /* As long as we're not replaying, just forward the request.  */
  if (!record_btrace_is_replaying ())
    {
      for (ops = ops->beneath; ops != NULL; ops = ops->beneath)
	if (ops->to_resume != NULL)
	  return ops->to_resume (ops, ptid, step, signal);

      error (_("Cannot find target for stepping."));
    }

  error (_("You can't do this from here.  Do 'record goto end', first."));
}

/* The to_wait method of target record-btrace.  */

static ptid_t
record_btrace_wait (struct target_ops *ops, ptid_t ptid,
		    struct target_waitstatus *status, int options)
{
  /* As long as we're not replaying, just forward the request.  */
  if (!record_btrace_is_replaying ())
    {
      for (ops = ops->beneath; ops != NULL; ops = ops->beneath)
	if (ops->to_wait != NULL)
	  return ops->to_wait (ops, ptid, status, options);

      error (_("Cannot find target for waiting."));
    }

  error (_("You can't do this from here.  Do 'record goto end', first."));
}

/* The to_find_new_threads method of target record-btrace.  */

static void
record_btrace_find_new_threads (struct target_ops *ops)
{
  /* Don't expect new threads if we're replaying.  */
  if (record_btrace_is_replaying ())
    return;

  /* Forward the request.  */
  for (ops = ops->beneath; ops != NULL; ops = ops->beneath)
    if (ops->to_find_new_threads != NULL)
      {
	ops->to_find_new_threads (ops);
	break;
      }
}

/* The to_thread_alive method of target record-btrace.  */

static int
record_btrace_thread_alive (struct target_ops *ops, ptid_t ptid)
{
  /* We don't add or remove threads during replay.  */
  if (record_btrace_is_replaying ())
    return find_thread_ptid (ptid) != NULL;

  /* Forward the request.  */
  for (ops = ops->beneath; ops != NULL; ops = ops->beneath)
    if (ops->to_thread_alive != NULL)
      return ops->to_thread_alive (ops, ptid);

  return 0;
}

/* Set the replay branch trace instruction iterator.  If IT is NULL, replay
   is stopped.  */

static void
record_btrace_set_replay (struct thread_info *tp,
			  const struct btrace_insn_iterator *it)
{
  struct btrace_thread_info *btinfo;

  btinfo = &tp->btrace;

  if (it == NULL || it->function == NULL)
    {
      if (btinfo->replay == NULL)
	return;

      xfree (btinfo->replay);
      btinfo->replay = NULL;
    }
  else
    {
      if (btinfo->replay == NULL)
	btinfo->replay = xmalloc (sizeof (*btinfo->replay));
      else if (btrace_insn_cmp (btinfo->replay, it) == 0)
	return;

      *btinfo->replay = *it;
    }

  /* Clear the function call and instruction histories so we start anew
     from the new replay position.  */
  xfree (btinfo->insn_history);
  xfree (btinfo->call_history);

  btinfo->insn_history = NULL;
  btinfo->call_history = NULL;

  registers_changed_ptid (tp->ptid);
}

/* The to_goto_record_begin method of target record-btrace.  */

static void
record_btrace_goto_begin (void)
{
  struct thread_info *tp;
  struct btrace_insn_iterator begin;

  tp = require_btrace_thread ();

  btrace_insn_begin (&begin, &tp->btrace);
  record_btrace_set_replay (tp, &begin);

  print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
}

/* The to_goto_record_end method of target record-btrace.  */

static void
record_btrace_goto_end (void)
{
  struct thread_info *tp;

  tp = require_btrace_thread ();

  record_btrace_set_replay (tp, NULL);

  print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
}

/* The to_goto_record method of target record-btrace.  */

static void
record_btrace_goto (ULONGEST insn)
{
  struct thread_info *tp;
  struct btrace_insn_iterator it;
  unsigned int number;
  int found;

  number = insn;

  /* Check for wrap-arounds.  */
  if (number != insn)
    error (_("Instruction number out of range."));

  tp = require_btrace_thread ();

  found = btrace_find_insn_by_number (&it, &tp->btrace, number);
  if (found == 0)
    error (_("No such instruction."));

  record_btrace_set_replay (tp, &it);

  print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
}

/* Initialize the record-btrace target ops.  */

static void
init_record_btrace_ops (void)
{
  struct target_ops *ops;

  ops = &record_btrace_ops;
  ops->to_shortname = "record-btrace";
  ops->to_longname = "Branch tracing target";
  ops->to_doc = "Collect control-flow trace and provide the execution history.";
  ops->to_open = record_btrace_open;
  ops->to_close = record_btrace_close;
  ops->to_detach = record_detach;
  ops->to_disconnect = record_disconnect;
  ops->to_mourn_inferior = record_mourn_inferior;
  ops->to_kill = record_kill;
  ops->to_create_inferior = find_default_create_inferior;
  ops->to_stop_recording = record_btrace_stop_recording;
  ops->to_info_record = record_btrace_info;
  ops->to_insn_history = record_btrace_insn_history;
  ops->to_insn_history_from = record_btrace_insn_history_from;
  ops->to_insn_history_range = record_btrace_insn_history_range;
  ops->to_call_history = record_btrace_call_history;
  ops->to_call_history_from = record_btrace_call_history_from;
  ops->to_call_history_range = record_btrace_call_history_range;
  ops->to_record_is_replaying = record_btrace_is_replaying;
  ops->to_xfer_partial = record_btrace_xfer_partial;
  ops->to_remove_breakpoint = record_btrace_remove_breakpoint;
  ops->to_insert_breakpoint = record_btrace_insert_breakpoint;
  ops->to_fetch_registers = record_btrace_fetch_registers;
  ops->to_store_registers = record_btrace_store_registers;
  ops->to_prepare_to_store = record_btrace_prepare_to_store;
  ops->to_get_unwinder = &record_btrace_frame_unwind;
  ops->to_get_tailcall_unwinder = &record_btrace_tailcall_frame_unwind;
  ops->to_resume = record_btrace_resume;
  ops->to_wait = record_btrace_wait;
  ops->to_find_new_threads = record_btrace_find_new_threads;
  ops->to_thread_alive = record_btrace_thread_alive;
  ops->to_goto_record_begin = record_btrace_goto_begin;
  ops->to_goto_record_end = record_btrace_goto_end;
  ops->to_goto_record = record_btrace_goto;
  ops->to_stratum = record_stratum;
  ops->to_magic = OPS_MAGIC;
}

/* Alias for "target record".  */

static void
cmd_record_btrace_start (char *args, int from_tty)
{
  if (args != NULL && *args != 0)
    error (_("Invalid argument."));

  execute_command ("target record-btrace", from_tty);
}

void _initialize_record_btrace (void);

/* Initialize btrace commands.  */

void
_initialize_record_btrace (void)
{
  add_cmd ("btrace", class_obscure, cmd_record_btrace_start,
	   _("Start branch trace recording."),
	   &record_cmdlist);
  add_alias_cmd ("b", "btrace", class_obscure, 1, &record_cmdlist);

  init_record_btrace_ops ();
  add_target (&record_btrace_ops);

  bfcache = htab_create_alloc (50, bfcache_hash, bfcache_eq, NULL,
			       xcalloc, xfree);
}