[PATCH 3/3] Create arch_lwp_info class hierarchy

[Simon Marchi <simon dot marchi at ericsson dot com>]

From: Simon Marchi <simon.marchi@polymtl.ca>

I am trying to "poison" the XNEW family of functions as well as xfree to
help catch their uses on non-POD types.  It trips on this:

/usr/include/c++/5/type_traits: In instantiation of ‘struct std::is_pod<arch_lwp_info>’:
/home/emaisin/src/binutils-gdb/gdb/common/traits.h:66:8:   required from ‘struct gdb::Or<std::is_pod<arch_lwp_info>, std::is_void<arch_lwp_info> >’
/home/emaisin/src/binutils-gdb/gdb/common/common-utils.h:59:15:   required from ‘void xfree(T*) [with T = arch_lwp_info]’
/home/emaisin/src/binutils-gdb/gdb/linux-nat.c:840:26:   required from here
/usr/include/c++/5/type_traits:656:12: error: invalid use of incomplete type ‘struct arch_lwp_info’
     struct is_pod
            ^

The problem is that the arch_lwp_info type is defined internally by the
various arch-specific linux-nat implementations in GDB and GDBserver,
but opaque to linux-nat.c.  When linux-nat.c tries to xfree an object of
incomplete type arch_lwp_info, it can't validate whether it is POD or
not.  This patch converts this to a proper class hierarchy, with
arch_lwp_info being an abstract class, and various arches defining their
own type extending it.

This will allow using C++ features in these objects, if we ever need to.

gdb/ChangeLog:

	* nat/linux-nat.h (arch_lwp_info): Define type, add virtual pure
	destructor.
	* linux-nat.h (struct arch_lwp_info): Remove forward
	declaration.
	(lwp_info) <arch_private>: Change type to use unique_ptr.
	* linux-nat.c (arch_lwp_info::~arch_lwp_info): Provide default
	implementation.
	(lwp_set_arch_private_info, lwp_arch_private_info): Adapt to use
	unique_ptr.
	(lwp_free): Don't free lp->arch_private manually.
	* arm-linux-nat.c (struct arch_lwp_info): Rename to ...
	(struct arm_lwp_info): ... this, inherit arch_lwp_info,
	initialize fields.
	(update_registers_callback): Allocate arm_lwp_info with new,
	adjust to unique_ptr usage.
	(arm_linux_new_thread): Likewise.
	(arm_linux_prepare_to_resume): Adjust to unique_ptr usage.
	* s390-linux-nat.c (struct arch_lwp_info): Rename to ...
	(s390_lwp_info): ... this, inherit arch_lwp_info, initialize
	fields.
	(s390_prepare_to_resume): Add cast.
	(s390_mark_per_info_changed): Allocate s390_lwp_info with new,
	add cast.
	* nat/aarch64-linux-hw-point.h (struct arch_lwp_info): Rename
	to ...
	(struct aarch64_lwp_info): ... this, inherit arch_lwp_info,
	initialize fields.
	* nat/aarch64-linux-hw-point.c (debug_reg_change_callback): Add
	cast, allocate aarch64_lwp_info with new.
	* nat/aarch64-linux.c (aarch64_linux_prepare_to_resume): Add
	cast.
	(aarch64_linux_new_thread): Allocate aarch64_lwp_info with new.
	* x86-linux.c (struct arch_lwp_info): Rename to ...
	(struct x86_lwp_info): ... this, inherit arch_lwp_info, initialize
	fields.
	(lwp_set_debug_registers_changed): Allocate x86_lwp_info with
	new, add cast.
	(lwp_debug_registers_changed): Add cast.

gdb/gdbserver/ChangeLog:

	* linux-low.h (struct lwp_info) <arch_private> Change type to
	unique_ptr.
	* linux-arm-low.c (struct arch_lwp_info): Rename to ...
	(struct arm_lwp_info): ... this, inherit arch_lwp_info, initialize
	fields.
	(update_registers_callback, arm_stopped_by_watchpoint,
	arm_stopped_data_address): Use lwp_arch_private_info and add cast.
	(arm_new_thread): Allocate arm_lwp_info with new, use
	lwp_set_arch_private_info.
	(arm_new_fork, arm_prepare_to_resume): Use
	lwp_arch_private_info and add cast.
	* linux-low.c (delete_lwp): Don't manually free arch_private.
	(lwp_set_arch_private_info, lwp_arch_private_info): Adapt to use
	unique_ptr.
	(arch_lwp_info::~arch_lwp_info): Provide default implementation.
	* linux-mips-low.c (struct arch_lwp_info): Rename to ...
	(struct mips_lwp_info): ... this, inherit arch_lwp_info, initialize
	fields.
	(update_watch_registers_callback): Use lwp_arch_private_info and
	add cast.
	(mips_linux_new_thread): Allocate mips_lwp_info with new, use
	lwp_arch_private_info.
	(mips_linux_prepare_to_resume): Use lwp_arch_private_info and add cast.
---
 gdb/arm-linux-nat.c              | 21 ++++++++++++---------
 gdb/gdbserver/linux-arm-low.c    | 31 +++++++++++++++++--------------
 gdb/gdbserver/linux-low.c        |  7 ++++---
 gdb/gdbserver/linux-low.h        |  2 +-
 gdb/gdbserver/linux-mips-low.c   | 16 +++++++++-------
 gdb/linux-nat.c                  |  7 ++++---
 gdb/linux-nat.h                  |  4 +---
 gdb/nat/aarch64-linux-hw-point.c |  4 ++--
 gdb/nat/aarch64-linux-hw-point.h |  6 +++---
 gdb/nat/aarch64-linux.c          |  4 ++--
 gdb/nat/linux-nat.h              |  7 ++++++-
 gdb/nat/x86-linux.c              | 12 +++++++-----
 gdb/s390-linux-nat.c             | 11 ++++++-----
 13 files changed, 74 insertions(+), 58 deletions(-)

diff --git a/gdb/arm-linux-nat.c b/gdb/arm-linux-nat.c
index ad3085a..19f9926 100644
--- a/gdb/arm-linux-nat.c
+++ b/gdb/arm-linux-nat.c
@@ -726,11 +726,11 @@ struct arm_linux_process_info
 };
 
 /* Per-thread arch-specific data we want to keep.  */
-struct arch_lwp_info
+struct arm_lwp_info : public arch_lwp_info
 {
   /* Non-zero if our copy differs from what's recorded in the thread.  */
-  char bpts_changed[MAX_BPTS];
-  char wpts_changed[MAX_WPTS];
+  char bpts_changed[MAX_BPTS] = {0};
+  char wpts_changed[MAX_WPTS] = {0};
 };
 
 static struct arm_linux_process_info *arm_linux_process_list = NULL;
@@ -928,14 +928,16 @@ update_registers_callback (struct lwp_info *lwp, void *arg)
   struct update_registers_data *data = (struct update_registers_data *) arg;
 
   if (lwp->arch_private == NULL)
-    lwp->arch_private = XCNEW (struct arch_lwp_info);
+    lwp->arch_private.reset (new arm_lwp_info);
+
+  struct arm_lwp_info *info = (arm_lwp_info *) lwp->arch_private.get ();
 
   /* The actual update is done later just before resuming the lwp,
      we just mark that the registers need updating.  */
   if (data->watch)
-    lwp->arch_private->wpts_changed[data->index] = 1;
+    info->wpts_changed[data->index] = 1;
   else
-    lwp->arch_private->bpts_changed[data->index] = 1;
+    info->bpts_changed[data->index] = 1;
 
   /* If the lwp isn't stopped, force it to momentarily pause, so
      we can update its breakpoint registers.  */
@@ -1186,7 +1188,7 @@ static void
 arm_linux_new_thread (struct lwp_info *lp)
 {
   int i;
-  struct arch_lwp_info *info = XCNEW (struct arch_lwp_info);
+  struct arm_lwp_info *info = new arm_lwp_info;
 
   /* Mark that all the hardware breakpoint/watchpoint register pairs
      for this thread need to be initialized.  */
@@ -1197,7 +1199,7 @@ arm_linux_new_thread (struct lwp_info *lp)
       info->wpts_changed[i] = 1;
     }
 
-  lp->arch_private = info;
+  lp->arch_private.reset (info);
 }
 
 /* Called when resuming a thread.
@@ -1208,7 +1210,8 @@ arm_linux_prepare_to_resume (struct lwp_info *lwp)
 {
   int pid, i;
   struct arm_linux_hw_breakpoint *bpts, *wpts;
-  struct arch_lwp_info *arm_lwp_info = lwp->arch_private;
+  struct arm_lwp_info *arm_lwp_info
+    = (struct arm_lwp_info *) lwp->arch_private.get ();
 
   pid = ptid_get_lwp (lwp->ptid);
   bpts = arm_linux_get_debug_reg_state (ptid_get_pid (lwp->ptid))->bpts;
diff --git a/gdb/gdbserver/linux-arm-low.c b/gdb/gdbserver/linux-arm-low.c
index 5a3f465..9e28388 100644
--- a/gdb/gdbserver/linux-arm-low.c
+++ b/gdb/gdbserver/linux-arm-low.c
@@ -110,13 +110,14 @@ struct arch_process_info
 };
 
 /* Per-thread arch-specific data we want to keep.  */
-struct arch_lwp_info
+struct arm_lwp_info : public arch_lwp_info
 {
   /* Non-zero if our copy differs from what's recorded in the thread.  */
-  char bpts_changed[MAX_BPTS];
-  char wpts_changed[MAX_WPTS];
+  char bpts_changed[MAX_BPTS] = {0};
+  char wpts_changed[MAX_WPTS] = {0};
+
   /* Cached stopped data address.  */
-  CORE_ADDR stopped_data_address;
+  CORE_ADDR stopped_data_address = 0;
 };
 
 /* These are in <asm/elf.h> in current kernels.  */
@@ -471,6 +472,7 @@ update_registers_callback (struct inferior_list_entry *entry, void *arg)
 {
   struct thread_info *thread = (struct thread_info *) entry;
   struct lwp_info *lwp = get_thread_lwp (thread);
+  arm_lwp_info *arm_lwp = (arm_lwp_info *) lwp_arch_private_info (lwp);
   struct update_registers_data *data = (struct update_registers_data *) arg;
 
   /* Only update the threads of the current process.  */
@@ -479,9 +481,9 @@ update_registers_callback (struct inferior_list_entry *entry, void *arg)
       /* The actual update is done later just before resuming the lwp,
          we just mark that the registers need updating.  */
       if (data->watch)
-	lwp->arch_private->wpts_changed[data->i] = 1;
+	arm_lwp->wpts_changed[data->i] = 1;
       else
-	lwp->arch_private->bpts_changed[data->i] = 1;
+	arm_lwp->bpts_changed[data->i] = 1;
 
       /* If the lwp isn't stopped, force it to momentarily pause, so
          we can update its breakpoint registers.  */
@@ -594,6 +596,7 @@ static int
 arm_stopped_by_watchpoint (void)
 {
   struct lwp_info *lwp = get_thread_lwp (current_thread);
+  arm_lwp_info *arm_lwp = (arm_lwp_info *) lwp_arch_private_info (lwp);
   siginfo_t siginfo;
 
   /* We must be able to set hardware watchpoints.  */
@@ -617,8 +620,7 @@ arm_stopped_by_watchpoint (void)
     return 0;
 
   /* Cache stopped data address for use by arm_stopped_data_address.  */
-  lwp->arch_private->stopped_data_address
-    = (CORE_ADDR) (uintptr_t) siginfo.si_addr;
+  arm_lwp->stopped_data_address = (CORE_ADDR) (uintptr_t) siginfo.si_addr;
 
   return 1;
 }
@@ -629,7 +631,8 @@ static CORE_ADDR
 arm_stopped_data_address (void)
 {
   struct lwp_info *lwp = get_thread_lwp (current_thread);
-  return lwp->arch_private->stopped_data_address;
+  arm_lwp_info *arm_lwp = (arm_lwp_info *) lwp_arch_private_info (lwp);
+  return arm_lwp->stopped_data_address;
 }
 
 /* Called when a new process is created.  */
@@ -644,7 +647,7 @@ arm_new_process (void)
 static void
 arm_new_thread (struct lwp_info *lwp)
 {
-  struct arch_lwp_info *info = XCNEW (struct arch_lwp_info);
+  arm_lwp_info *info = new arm_lwp_info;
   int i;
 
   for (i = 0; i < MAX_BPTS; i++)
@@ -652,7 +655,7 @@ arm_new_thread (struct lwp_info *lwp)
   for (i = 0; i < MAX_WPTS; i++)
     info->wpts_changed[i] = 1;
 
-  lwp->arch_private = info;
+  lwp_set_arch_private_info (lwp, info);
 }
 
 static void
@@ -661,7 +664,6 @@ arm_new_fork (struct process_info *parent, struct process_info *child)
   struct arch_process_info *parent_proc_info;
   struct arch_process_info *child_proc_info;
   struct lwp_info *child_lwp;
-  struct arch_lwp_info *child_lwp_info;
   int i;
 
   /* These are allocated by linux_add_process.  */
@@ -692,7 +694,8 @@ arm_new_fork (struct process_info *parent, struct process_info *child)
   /* Mark all the hardware breakpoints and watchpoints as changed to
      make sure that the registers will be updated.  */
   child_lwp = find_lwp_pid (ptid_of (child));
-  child_lwp_info = child_lwp->arch_private;
+  arm_lwp_info *child_lwp_info
+    = (arm_lwp_info *) lwp_arch_private_info (child_lwp);
   for (i = 0; i < MAX_BPTS; i++)
     child_lwp_info->bpts_changed[i] = 1;
   for (i = 0; i < MAX_WPTS; i++)
@@ -708,7 +711,7 @@ arm_prepare_to_resume (struct lwp_info *lwp)
   int pid = lwpid_of (thread);
   struct process_info *proc = find_process_pid (pid_of (thread));
   struct arch_process_info *proc_info = proc->priv->arch_private;
-  struct arch_lwp_info *lwp_info = lwp->arch_private;
+  arm_lwp_info *lwp_info = (arm_lwp_info *) lwp_arch_private_info (lwp);
   int i;
 
   for (i = 0; i < arm_linux_get_hw_breakpoint_count (); i++)
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index e650b0d..5decca7 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -152,7 +152,7 @@ void
 lwp_set_arch_private_info (struct lwp_info *lwp,
 			   struct arch_lwp_info *info)
 {
-  lwp->arch_private = info;
+  lwp->arch_private.reset (info);
 }
 
 /* See nat/linux-nat.h.  */
@@ -160,7 +160,7 @@ lwp_set_arch_private_info (struct lwp_info *lwp,
 struct arch_lwp_info *
 lwp_arch_private_info (struct lwp_info *lwp)
 {
-  return lwp->arch_private;
+  return lwp->arch_private.get ()	;
 }
 
 /* See nat/linux-nat.h.  */
@@ -414,7 +414,6 @@ delete_lwp (struct lwp_info *lwp)
     debug_printf ("deleting %ld\n", lwpid_of (thr));
 
   remove_thread (thr);
-  free (lwp->arch_private);
   delete lwp;
 }
 
@@ -7588,6 +7587,8 @@ linux_get_pc_64bit (struct regcache *regcache)
   return pc;
 }
 
+arch_lwp_info::~arch_lwp_info () = default;
+
 
 static struct target_ops linux_target_ops = {
   linux_create_inferior,
diff --git a/gdb/gdbserver/linux-low.h b/gdb/gdbserver/linux-low.h
index dcc9315..43c1735 100644
--- a/gdb/gdbserver/linux-low.h
+++ b/gdb/gdbserver/linux-low.h
@@ -377,7 +377,7 @@ struct lwp_info
 #endif
 
   /* Arch-specific additions.  */
-  struct arch_lwp_info *arch_private = NULL;
+  std::unique_ptr<arch_lwp_info> arch_private;
 };
 
 int linux_pid_exe_is_elf_64_file (int pid, unsigned int *machine);
diff --git a/gdb/gdbserver/linux-mips-low.c b/gdb/gdbserver/linux-mips-low.c
index b4a83b0..b09a099 100644
--- a/gdb/gdbserver/linux-mips-low.c
+++ b/gdb/gdbserver/linux-mips-low.c
@@ -188,10 +188,10 @@ struct arch_process_info
 
 /* Per-thread arch-specific data we want to keep.  */
 
-struct arch_lwp_info
+struct mips_lwp_info : public arch_lwp_info
 {
   /* Non-zero if our copy differs from what's recorded in the thread.  */
-  int watch_registers_changed;
+  int watch_registers_changed = 0;
 };
 
 /* From mips-linux-nat.c.  */
@@ -298,6 +298,7 @@ update_watch_registers_callback (struct inferior_list_entry *entry,
 {
   struct thread_info *thread = (struct thread_info *) entry;
   struct lwp_info *lwp = get_thread_lwp (thread);
+  mips_lwp_info *mips_lwp = (mips_lwp_info *) lwp_arch_private_info (lwp);
   int pid = *(int *) pid_p;
 
   /* Only update the threads of this process.  */
@@ -305,7 +306,7 @@ update_watch_registers_callback (struct inferior_list_entry *entry,
     {
       /* The actual update is done later just before resuming the lwp,
 	 we just mark that the registers need updating.  */
-      lwp->arch_private->watch_registers_changed = 1;
+      mips_lwp->watch_registers_changed = 1;
 
       /* If the lwp isn't stopped, force it to momentarily pause, so
 	 we can update its watch registers.  */
@@ -334,11 +335,11 @@ mips_linux_new_process (void)
 static void
 mips_linux_new_thread (struct lwp_info *lwp)
 {
-  struct arch_lwp_info *info = XCNEW (struct arch_lwp_info);
+  mips_lwp_info *info = new mips_lwp_info;
 
   info->watch_registers_changed = 1;
 
-  lwp->arch_private = info;
+  lwp_set_arch_private_info (lwp, info);
 }
 
 /* Create a new mips_watchpoint and add it to the list.  */
@@ -413,8 +414,9 @@ mips_linux_prepare_to_resume (struct lwp_info *lwp)
   ptid_t ptid = ptid_of (get_lwp_thread (lwp));
   struct process_info *proc = find_process_pid (ptid_get_pid (ptid));
   struct arch_process_info *priv = proc->priv->arch_private;
+  mips_lwp_info *mips_lwp = (mips_lwp_info *) lwp_arch_private_info (lwp);
 
-  if (lwp->arch_private->watch_registers_changed)
+  if (mips_lwp->watch_registers_changed)
     {
       /* Only update the watch registers if we have set or unset a
 	 watchpoint already.  */
@@ -428,7 +430,7 @@ mips_linux_prepare_to_resume (struct lwp_info *lwp)
 	    perror_with_name ("Couldn't write watch register");
 	}
 
-      lwp->arch_private->watch_registers_changed = 0;
+      mips_lwp->watch_registers_changed = 0;
     }
 }
 
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 9378276..130a4d4 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -322,13 +322,15 @@ ptid_of_lwp (struct lwp_info *lwp)
   return lwp->ptid;
 }
 
+arch_lwp_info::~arch_lwp_info () = default;
+
 /* See nat/linux-nat.h.  */
 
 void
 lwp_set_arch_private_info (struct lwp_info *lwp,
 			   struct arch_lwp_info *info)
 {
-  lwp->arch_private = info;
+  lwp->arch_private.reset (info);
 }
 
 /* See nat/linux-nat.h.  */
@@ -336,7 +338,7 @@ lwp_set_arch_private_info (struct lwp_info *lwp,
 struct arch_lwp_info *
 lwp_arch_private_info (struct lwp_info *lwp)
 {
-  return lwp->arch_private;
+  return lwp->arch_private.get ();
 }
 
 /* See nat/linux-nat.h.  */
@@ -837,7 +839,6 @@ static int check_ptrace_stopped_lwp_gone (struct lwp_info *lp);
 static void
 lwp_free (struct lwp_info *lp)
 {
-  xfree (lp->arch_private);
   delete lp;
 }
 
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index a783674..57fab42 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -21,8 +21,6 @@
 #include "target.h"
 #include <signal.h>
 
-struct arch_lwp_info;
-
 /* Structure describing an LWP.  This is public only for the purposes
    of ALL_LWPS; target-specific code should generally not access it
    directly.  */
@@ -103,7 +101,7 @@ struct lwp_info
   int core = -1;
 
   /* Arch-specific additions.  */
-  arch_lwp_info *arch_private = NULL;
+  std::unique_ptr<arch_lwp_info> arch_private;
 
   /* Previous and next pointers in doubly-linked list of known LWPs,
      sorted by reverse creation order.  */
diff --git a/gdb/nat/aarch64-linux-hw-point.c b/gdb/nat/aarch64-linux-hw-point.c
index 9800d9a..bba2200 100644
--- a/gdb/nat/aarch64-linux-hw-point.c
+++ b/gdb/nat/aarch64-linux-hw-point.c
@@ -258,13 +258,13 @@ debug_reg_change_callback (struct lwp_info *lwp, void *ptr)
   int tid = ptid_get_lwp (ptid_of_lwp (lwp));
   int idx = param_p->idx;
   int is_watchpoint = param_p->is_watchpoint;
-  struct arch_lwp_info *info = lwp_arch_private_info (lwp);
+  aarch64_lwp_info *info = (aarch64_lwp_info *) lwp_arch_private_info (lwp);
   dr_changed_t *dr_changed_ptr;
   dr_changed_t dr_changed;
 
   if (info == NULL)
     {
-      info = XCNEW (struct arch_lwp_info);
+      info = new aarch64_lwp_info;
       lwp_set_arch_private_info (lwp, info);
     }
 
diff --git a/gdb/nat/aarch64-linux-hw-point.h b/gdb/nat/aarch64-linux-hw-point.h
index 610a5f1..6547594 100644
--- a/gdb/nat/aarch64-linux-hw-point.h
+++ b/gdb/nat/aarch64-linux-hw-point.h
@@ -154,13 +154,13 @@ struct aarch64_debug_reg_state
 
 /* Per-thread arch-specific data we want to keep.  */
 
-struct arch_lwp_info
+struct aarch64_lwp_info : public arch_lwp_info
 {
   /* When bit N is 1, it indicates the Nth hardware breakpoint or
      watchpoint register pair needs to be updated when the thread is
      resumed; see aarch64_linux_prepare_to_resume.  */
-  dr_changed_t dr_changed_bp;
-  dr_changed_t dr_changed_wp;
+  dr_changed_t dr_changed_bp = 0;
+  dr_changed_t dr_changed_wp = 0;
 };
 
 extern int aarch64_num_bp_regs;
diff --git a/gdb/nat/aarch64-linux.c b/gdb/nat/aarch64-linux.c
index 388eee8..12999da 100644
--- a/gdb/nat/aarch64-linux.c
+++ b/gdb/nat/aarch64-linux.c
@@ -33,7 +33,7 @@
 void
 aarch64_linux_prepare_to_resume (struct lwp_info *lwp)
 {
-  struct arch_lwp_info *info = lwp_arch_private_info (lwp);
+    aarch64_lwp_info *info = (aarch64_lwp_info *) lwp_arch_private_info (lwp);
 
   /* NULL means this is the main thread still going through the shell,
      or, no watchpoint has been set yet.  In that case, there's
@@ -73,7 +73,7 @@ aarch64_linux_prepare_to_resume (struct lwp_info *lwp)
 void
 aarch64_linux_new_thread (struct lwp_info *lwp)
 {
-  struct arch_lwp_info *info = XNEW (struct arch_lwp_info);
+  aarch64_lwp_info *info = new aarch64_lwp_info;
 
   /* Mark that all the hardware breakpoint/watchpoint register pairs
      for this thread need to be initialized (with data from
diff --git a/gdb/nat/linux-nat.h b/gdb/nat/linux-nat.h
index 7dd18fe..751f32c 100644
--- a/gdb/nat/linux-nat.h
+++ b/gdb/nat/linux-nat.h
@@ -23,7 +23,12 @@
 #include "target/waitstatus.h"
 
 struct lwp_info;
-struct arch_lwp_info;
+
+/* Base class for arch-specific lwp data.  */
+struct arch_lwp_info
+{
+  virtual ~arch_lwp_info () = 0;
+};
 
 /* This is the kernel's hard limit.  Not to be confused with SIGRTMIN.  */
 #ifndef __SIGRTMIN
diff --git a/gdb/nat/x86-linux.c b/gdb/nat/x86-linux.c
index b499e74..b35ed19 100644
--- a/gdb/nat/x86-linux.c
+++ b/gdb/nat/x86-linux.c
@@ -23,11 +23,11 @@
 
 /* Per-thread arch-specific data we want to keep.  */
 
-struct arch_lwp_info
+struct x86_lwp_info : public arch_lwp_info
 {
   /* Non-zero if our copy differs from what's recorded in the
      thread.  */
-  int debug_registers_changed;
+  int debug_registers_changed = 0;
 };
 
 /* See nat/x86-linux.h.  */
@@ -36,9 +36,11 @@ void
 lwp_set_debug_registers_changed (struct lwp_info *lwp, int value)
 {
   if (lwp_arch_private_info (lwp) == NULL)
-    lwp_set_arch_private_info (lwp, XCNEW (struct arch_lwp_info));
+    lwp_set_arch_private_info (lwp, new x86_lwp_info ());
 
-  lwp_arch_private_info (lwp)->debug_registers_changed = value;
+  x86_lwp_info *info = (x86_lwp_info *) lwp_arch_private_info (lwp);
+
+  info->debug_registers_changed = value;
 }
 
 /* See nat/x86-linux.h.  */
@@ -46,7 +48,7 @@ lwp_set_debug_registers_changed (struct lwp_info *lwp, int value)
 int
 lwp_debug_registers_changed (struct lwp_info *lwp)
 {
-  struct arch_lwp_info *info = lwp_arch_private_info (lwp);
+  x86_lwp_info *info = (x86_lwp_info *) lwp_arch_private_info (lwp);
 
   /* NULL means either that this is the main thread still going
      through the shell, or that no watchpoint has been set yet.
diff --git a/gdb/s390-linux-nat.c b/gdb/s390-linux-nat.c
index 90c73c4..4e38f16 100644
--- a/gdb/s390-linux-nat.c
+++ b/gdb/s390-linux-nat.c
@@ -44,10 +44,10 @@
 
 /* Per-thread arch-specific data.  */
 
-struct arch_lwp_info
+struct s390_lwp_info : public arch_lwp_info
 {
   /* Non-zero if the thread's PER info must be re-written.  */
-  int per_info_changed;
+  int per_info_changed = 0;
 };
 
 static int have_regset_last_break = 0;
@@ -665,7 +665,7 @@ s390_prepare_to_resume (struct lwp_info *lp)
   CORE_ADDR watch_lo_addr = (CORE_ADDR)-1, watch_hi_addr = 0;
   unsigned ix;
   s390_watch_area *area;
-  struct arch_lwp_info *lp_priv = lwp_arch_private_info (lp);
+  s390_lwp_info *lp_priv = (s390_lwp_info *) lwp_arch_private_info (lp);
   struct s390_debug_reg_state *state = s390_get_debug_reg_state (pid);
   int step = lwp_is_stepping (lp);
 
@@ -763,9 +763,10 @@ static void
 s390_mark_per_info_changed (struct lwp_info *lp)
 {
   if (lwp_arch_private_info (lp) == NULL)
-    lwp_set_arch_private_info (lp, XCNEW (struct arch_lwp_info));
+    lwp_set_arch_private_info (lp, new s390_lwp_info);
 
-  lwp_arch_private_info (lp)->per_info_changed = 1;
+  s390_lwp_info *lp_private = (s390_lwp_info *) lwp_arch_private_info (lp);
+  lp_private->per_info_changed = 1;
 }
 
 /* When attaching to a new thread, mark its PER info as changed.  */
-- 
2.7.4