Re: [PATCH] Place displaced step data directly in inferior structure

[Philippe Waroquiers <philippe dot waroquiers at skynet dot be>]

Isn't/wasn't this ready to be pushed ?

Thanks
Philippe


On Fri, 2018-11-23 at 21:05 +0000, Simon Marchi wrote:
> On 2018-11-23 2:47 p.m., Simon Marchi wrote:
> > I agree it would be nice to avoid that duplication.  I kept the asserts and
> > in-class initializations for step_thread and step_closure, because I think
> > having those asserts can be useful.
> > 
> > I also changed step_saved_copy to be a vector, this makes the job a bit easier
> > and plugs the leak identified in
> > 
> >   https://sourceware.org/ml/gdb-patches/2018-11/msg00220.html
> > 
> > Technically we don't need to clear it... but if we didn't the comment
> > above "reset" would be a lie :).
> > 
> > Here's the updated patch (currently testing on the buildbot):
> 
> Ah damn it, there's a case where the assertion does not hold (gdb.base/step-over-exit.exp).
> So here's a simpler version of the patch where we just blindly reset everything to the
> default values (similar to what we do today).
> 
> 
> From 1587bbc5c67349a1429542989cf33b102109746e Mon Sep 17 00:00:00 2001
> From: Simon Marchi <simon.marchi@ericsson.com>
> Date: Wed, 21 Nov 2018 21:35:16 -0500
> Subject: [PATCH] Place displaced step data directly in inferior structure
> 
> This patch moves the per-inferior data related to displaced stepping to
> be directly in the inferior structure, rather than in a container on the
> side.
> 
> On notable difference is that previously, we deleted the state on
> inferior exit, which guaranteed a clean state if re-using the inferior
> for a new run or attach.  We now need to reset the state manually.
> 
> At the same time, I changed step_saved_copy to be a gdb::byte_vector, so
> it is automatically freed on destruction (which should plug the leak
> reported here [1]).
> 
> [1] https://sourceware.org/ml/gdb-patches/2018-11/msg00202.html
> 
> gdb/ChangeLog:
> 
> 	* inferior.h (class inferior) <displaced_step_state>: New field.
> 	* infrun.h (struct displaced_step_state): Move here from
> 	infrun.c.  Initialize fields, add constructor.
> 	<inf>: Remove field.
> 	<reset>: New method.
> 	* infrun.c (struct displaced_step_inferior_state): Move to
> 	infrun.h.
> 	(displaced_step_inferior_states): Remove.
> 	(get_displaced_stepping_state): Adust.
> 	(displaced_step_in_progress_any_inferior): Adjust.
> 	(displaced_step_in_progress_thread): Adjust.
> 	(displaced_step_in_progress): Adjust.
> 	(add_displaced_stepping_state): Remove.
> 	(get_displaced_step_closure_by_addr): Adjust.
> 	(remove_displaced_stepping_state): Remove.
> 	(infrun_inferior_exit): Call displaced_step_state.reset.
> 	(use_displaced_stepping): Don't check for NULL.
> 	(displaced_step_prepare_throw): Call
> 	get_displaced_stepping_state.
> 	(displaced_step_fixup): Don't check for NULL.
> 	(prepare_for_detach): Don't check for NULL.
> ---
>  gdb/inferior.h |   3 ++
>  gdb/infrun.c   | 142 +++++++------------------------------------------
>  gdb/infrun.h   |  44 +++++++++++++++
>  3 files changed, 67 insertions(+), 122 deletions(-)
> 
> diff --git a/gdb/inferior.h b/gdb/inferior.h
> index 33c2eac9d3c..1a3f579d8d2 100644
> --- a/gdb/inferior.h
> +++ b/gdb/inferior.h
> @@ -503,6 +503,9 @@ public:
>       this gdbarch.  */
>    struct gdbarch *gdbarch = NULL;
> 
> +  /* Data related to displaced stepping.  */
> +  displaced_step_inferior_state displaced_step_state;
> +
>    /* Per inferior data-pointers required by other GDB modules.  */
>    REGISTRY_FIELDS;
>  };
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 46a8985f860..cf216c7804e 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -1476,53 +1476,12 @@ step_over_info_valid_p (void)
> 
>  displaced_step_closure::~displaced_step_closure () = default;
> 
> -/* Per-inferior displaced stepping state.  */
> -struct displaced_step_inferior_state
> -{
> -  /* The process this displaced step state refers to.  */
> -  inferior *inf;
> -
> -  /* True if preparing a displaced step ever failed.  If so, we won't
> -     try displaced stepping for this inferior again.  */
> -  int failed_before;
> -
> -  /* If this is not nullptr, this is the thread carrying out a
> -     displaced single-step in process PID.  This thread's state will
> -     require fixing up once it has completed its step.  */
> -  thread_info *step_thread;
> -
> -  /* The architecture the thread had when we stepped it.  */
> -  struct gdbarch *step_gdbarch;
> -
> -  /* The closure provided gdbarch_displaced_step_copy_insn, to be used
> -     for post-step cleanup.  */
> -  struct displaced_step_closure *step_closure;
> -
> -  /* The address of the original instruction, and the copy we
> -     made.  */
> -  CORE_ADDR step_original, step_copy;
> -
> -  /* Saved contents of copy area.  */
> -  gdb_byte *step_saved_copy;
> -};
> -
> -/* The list of states of processes involved in displaced stepping
> -   presently.  */
> -static std::forward_list<displaced_step_inferior_state *>
> -  displaced_step_inferior_states;
> -
>  /* Get the displaced stepping state of process PID.  */
> 
>  static displaced_step_inferior_state *
>  get_displaced_stepping_state (inferior *inf)
>  {
> -  for (auto *state : displaced_step_inferior_states)
> -    {
> -      if (state->inf == inf)
> -	return state;
> -    }
> -
> -  return nullptr;
> +  return &inf->displaced_step_state;
>  }
> 
>  /* Returns true if any inferior has a thread doing a displaced
> @@ -1531,9 +1490,9 @@ get_displaced_stepping_state (inferior *inf)
>  static bool
>  displaced_step_in_progress_any_inferior ()
>  {
> -  for (auto *state : displaced_step_inferior_states)
> +  for (inferior *i : all_inferiors ())
>      {
> -      if (state->step_thread != nullptr)
> +      if (i->displaced_step_state.step_thread != nullptr)
>  	return true;
>      }
> 
> @@ -1546,13 +1505,9 @@ displaced_step_in_progress_any_inferior ()
>  static int
>  displaced_step_in_progress_thread (thread_info *thread)
>  {
> -  struct displaced_step_inferior_state *displaced;
> -
>    gdb_assert (thread != NULL);
> 
> -  displaced = get_displaced_stepping_state (thread->inf);
> -
> -  return (displaced != NULL && displaced->step_thread == thread);
> +  return get_displaced_stepping_state (thread->inf)->step_thread == thread;
>  }
> 
>  /* Return true if process PID has a thread doing a displaced step.  */
> @@ -1560,34 +1515,7 @@ displaced_step_in_progress_thread (thread_info *thread)
>  static int
>  displaced_step_in_progress (inferior *inf)
>  {
> -  struct displaced_step_inferior_state *displaced;
> -
> -  displaced = get_displaced_stepping_state (inf);
> -  if (displaced != NULL && displaced->step_thread != nullptr)
> -    return 1;
> -
> -  return 0;
> -}
> -
> -/* Add a new displaced stepping state for process PID to the displaced
> -   stepping state list, or return a pointer to an already existing
> -   entry, if it already exists.  Never returns NULL.  */
> -
> -static displaced_step_inferior_state *
> -add_displaced_stepping_state (inferior *inf)
> -{
> -  displaced_step_inferior_state *state
> -    = get_displaced_stepping_state (inf);
> -
> -  if (state != nullptr)
> -    return state;
> -
> -  state = XCNEW (struct displaced_step_inferior_state);
> -  state->inf = inf;
> -
> -  displaced_step_inferior_states.push_front (state);
> -
> -  return state;
> +  return get_displaced_stepping_state (inf)->step_thread != nullptr;
>  }
> 
>  /* If inferior is in displaced stepping, and ADDR equals to starting address
> @@ -1597,42 +1525,21 @@ add_displaced_stepping_state (inferior *inf)
>  struct displaced_step_closure*
>  get_displaced_step_closure_by_addr (CORE_ADDR addr)
>  {
> -  struct displaced_step_inferior_state *displaced
> +  displaced_step_inferior_state *displaced
>      = get_displaced_stepping_state (current_inferior ());
> 
>    /* If checking the mode of displaced instruction in copy area.  */
> -  if (displaced != NULL
> -      && displaced->step_thread != nullptr
> +  if (displaced->step_thread != nullptr
>        && displaced->step_copy == addr)
>      return displaced->step_closure;
> 
>    return NULL;
>  }
> 
> -/* Remove the displaced stepping state of process PID.  */
> -
> -static void
> -remove_displaced_stepping_state (inferior *inf)
> -{
> -  gdb_assert (inf != nullptr);
> -
> -  displaced_step_inferior_states.remove_if
> -    ([inf] (displaced_step_inferior_state *state)
> -      {
> -	if (state->inf == inf)
> -	  {
> -	    xfree (state);
> -	    return true;
> -	  }
> -	else
> -	  return false;
> -      });
> -}
> -
>  static void
>  infrun_inferior_exit (struct inferior *inf)
>  {
> -  remove_displaced_stepping_state (inf);
> +  inf->displaced_step_state.reset ();
>  }
> 
>  /* If ON, and the architecture supports it, GDB will use displaced
> @@ -1669,17 +1576,15 @@ use_displaced_stepping (struct thread_info *tp)
>  {
>    struct regcache *regcache = get_thread_regcache (tp);
>    struct gdbarch *gdbarch = regcache->arch ();
> -  struct displaced_step_inferior_state *displaced_state;
> -
> -  displaced_state = get_displaced_stepping_state (tp->inf);
> +  displaced_step_inferior_state *displaced_state
> +    = get_displaced_stepping_state (tp->inf);
> 
>    return (((can_use_displaced_stepping == AUTO_BOOLEAN_AUTO
>  	    && target_is_non_stop_p ())
>  	   || can_use_displaced_stepping == AUTO_BOOLEAN_TRUE)
>  	  && gdbarch_displaced_step_copy_insn_p (gdbarch)
>  	  && find_record_target () == NULL
> -	  && (displaced_state == NULL
> -	      || !displaced_state->failed_before));
> +	  && !displaced_state->failed_before);
>  }
> 
>  /* Clean out any stray displaced stepping state.  */
> @@ -1734,14 +1639,12 @@ displaced_step_dump_bytes (struct ui_file *file,
>  static int
>  displaced_step_prepare_throw (thread_info *tp)
>  {
> -  struct cleanup *ignore_cleanups;
>    regcache *regcache = get_thread_regcache (tp);
>    struct gdbarch *gdbarch = regcache->arch ();
>    const address_space *aspace = regcache->aspace ();
>    CORE_ADDR original, copy;
>    ULONGEST len;
>    struct displaced_step_closure *closure;
> -  struct displaced_step_inferior_state *displaced;
>    int status;
> 
>    /* We should never reach this function if the architecture does not
> @@ -1760,7 +1663,8 @@ displaced_step_prepare_throw (thread_info *tp)
>    /* We have to displaced step one thread at a time, as we only have
>       access to a single scratch space per inferior.  */
> 
> -  displaced = add_displaced_stepping_state (tp->inf);
> +  displaced_step_inferior_state *displaced
> +    = get_displaced_stepping_state (tp->inf);
> 
>    if (displaced->step_thread != nullptr)
>      {
> @@ -1816,10 +1720,8 @@ displaced_step_prepare_throw (thread_info *tp)
>      }
> 
>    /* Save the original contents of the copy area.  */
> -  displaced->step_saved_copy = (gdb_byte *) xmalloc (len);
> -  ignore_cleanups = make_cleanup (free_current_contents,
> -				  &displaced->step_saved_copy);
> -  status = target_read_memory (copy, displaced->step_saved_copy, len);
> +  displaced->step_saved_copy.resize (len);
> +  status = target_read_memory (copy, displaced->step_saved_copy.data (), len);
>    if (status != 0)
>      throw_error (MEMORY_ERROR,
>  		 _("Error accessing memory address %s (%s) for "
> @@ -1830,7 +1732,7 @@ displaced_step_prepare_throw (thread_info *tp)
>        fprintf_unfiltered (gdb_stdlog, "displaced: saved %s: ",
>  			  paddress (gdbarch, copy));
>        displaced_step_dump_bytes (gdb_stdlog,
> -				 displaced->step_saved_copy,
> +				 displaced->step_saved_copy.data (),
>  				 len);
>      };
> 
> @@ -1841,7 +1743,6 @@ displaced_step_prepare_throw (thread_info *tp)
>        /* The architecture doesn't know how or want to displaced step
>  	 this instruction or instruction sequence.  Fallback to
>  	 stepping over the breakpoint in-line.  */
> -      do_cleanups (ignore_cleanups);
>        return -1;
>      }
> 
> @@ -1853,7 +1754,8 @@ displaced_step_prepare_throw (thread_info *tp)
>    displaced->step_original = original;
>    displaced->step_copy = copy;
> 
> -  make_cleanup (displaced_step_clear_cleanup, displaced);
> +  cleanup *ignore_cleanups
> +    = make_cleanup (displaced_step_clear_cleanup, displaced);
> 
>    /* Resume execution at the copy.  */
>    regcache_write_pc (regcache, copy);
> @@ -1931,7 +1833,7 @@ displaced_step_restore (struct displaced_step_inferior_state *displaced,
>    ULONGEST len = gdbarch_max_insn_length (displaced->step_gdbarch);
> 
>    write_memory_ptid (ptid, displaced->step_copy,
> -		     displaced->step_saved_copy, len);
> +		     displaced->step_saved_copy.data (), len);
>    if (debug_displaced)
>      fprintf_unfiltered (gdb_stdlog, "displaced: restored %s %s\n",
>  			target_pid_to_str (ptid),
> @@ -1953,10 +1855,6 @@ displaced_step_fixup (thread_info *event_thread, enum gdb_signal signal)
>      = get_displaced_stepping_state (event_thread->inf);
>    int ret;
> 
> -  /* Was any thread of this process doing a displaced step?  */
> -  if (displaced == NULL)
> -    return 0;
> -
>    /* Was this event for the thread we displaced?  */
>    if (displaced->step_thread != event_thread)
>      return 0;
> @@ -3577,7 +3475,7 @@ prepare_for_detach (void)
> 
>    /* Is any thread of this process displaced stepping?  If not,
>       there's nothing else to do.  */
> -  if (displaced == NULL || displaced->step_thread == nullptr)
> +  if (displaced->step_thread == nullptr)
>      return;
> 
>    if (debug_infrun)
> diff --git a/gdb/infrun.h b/gdb/infrun.h
> index a701f0ca47f..1b243db057c 100644
> --- a/gdb/infrun.h
> +++ b/gdb/infrun.h
> @@ -258,4 +258,48 @@ struct buf_displaced_step_closure : displaced_step_closure
>    gdb::byte_vector buf;
>  };
> 
> +/* Per-inferior displaced stepping state.  */
> +struct displaced_step_inferior_state
> +{
> +  displaced_step_inferior_state ()
> +  {
> +    reset ();
> +  }
> +
> +  /* Put this object back in its original state.  */
> +  void reset ()
> +  {
> +    failed_before = 0;
> +    step_thread = nullptr;
> +    step_gdbarch = nullptr;
> +    step_closure = nullptr;
> +    step_original = 0;
> +    step_copy = 0;
> +    step_saved_copy.clear ();
> +  }
> +
> +  /* True if preparing a displaced step ever failed.  If so, we won't
> +     try displaced stepping for this inferior again.  */
> +  int failed_before;
> +
> +  /* If this is not nullptr, this is the thread carrying out a
> +     displaced single-step in process PID.  This thread's state will
> +     require fixing up once it has completed its step.  */
> +  thread_info *step_thread;
> +
> +  /* The architecture the thread had when we stepped it.  */
> +  gdbarch *step_gdbarch;
> +
> +  /* The closure provided gdbarch_displaced_step_copy_insn, to be used
> +     for post-step cleanup.  */
> +  displaced_step_closure *step_closure;
> +
> +  /* The address of the original instruction, and the copy we
> +     made.  */
> +  CORE_ADDR step_original, step_copy;
> +
> +  /* Saved contents of copy area.  */
> +  gdb::byte_vector step_saved_copy;
> +};
> +
>  #endif /* INFRUN_H */
> -- 
> 2.19.1
>