[PATCH 1/2] lwp_info; Make the arch code free arch_lwp_info

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

I have the goal of "poisoning" the XNEW/xfree-family of functions, so
that we catch their usages with non-POD types.  A few things need to be
fixed in the mean time, this is one.

The common lwp code in linux-nat.c and gdbserver/linux-low.c xfrees the
private lwp data of type arch_lwp_info.  However, that type is opaque
from its point of view, as its defined differently in each arch-specific
implementation.  This trips on the std::is_pod<T> check, since the
compiler can't tell whether the type is POD or not if it doesn't know
about it.

My initial patch [1] made a class hierarchy with a virtual destructor.
However, as Pedro pointed out, we only have one native architecture at
the time built in gdb and gdbserver, so that's overkill.  Instead, we
can move the responsibility of free'ing arch_lwp_info to the arch code
(which is also the one that allocated it in the first place).  This is
what this patch does.

Also, I had the concern that if we wanted to use C++ features in these
structures, we would have a problem with the one-definition rule.
However, since a build will only have one version of arch_lwp_info,
that's not a problem.

There are changes in arch-specific files, I was only able to built-test
this patch with the following cross-compilers:

  aarch64-linux-gnu
  alpha-linux-gnu
  arm-linux-gnueabihf
  hppa-linux-gnu
  m68k-linux-gnu
  mips64el-linux-gnuabi64
  powerpc64-linux-gnu
  s390x-linux-gnu
  sh4-linux-gnu
  sparc64-linux-gnu
  x86_64-linux-gnu
  x86_64-w64-mingw32

A buildbot run didn't find any regression.

[1] https://sourceware.org/ml/gdb-patches/2017-08/msg00255.html

gdb/ChangeLog:

	* linux-nat.h (linux_nat_set_delete_thread): New declaration.
	* linux-nat.c (linux_nat_delete_thread): New variable.
	(lwp_free): Invoke linux_nat_delete_thread if set.
	(linux_nat_set_delete_thread): New function.
	* aarch64-linux-nat.c (_initialize_aarch64_linux_nat): Assign
	thread delete callback.
	* arm-linux-nat.c (arm_linux_delete_thread): New function.
	(_initialize_arm_linux_nat): Assign thread delete callback.
	* s390-linux-nat.c (s390_delete_thread): New function.
	(_initialize_s390_nat): Assign thread delete callback.
	* x86-linux-nat.c (x86_linux_add_target): Likewise.
	* nat/aarch64-linux.c (aarch64_linux_delete_thread): New
	function.
	* nat/aarch64-linux.h (aarch64_linux_delete_thread): New
	declaration.
	* nat/x86-linux.c (x86_linux_delete_thread): New function.
	* nat/x86-linux.h (x86_linux_delete_thread): New declaration.

gdb/gdbserver/ChangeLog:

	* linux-aarch64-low.c (the_low_target): Add thread delete
	callback.
	* linux-arm-low.c (arm_delete_thread): New function.
	(the_low_target): Add thread delete callback.
	* linux-bfin-low.c (the_low_target): Likewise.
	* linux-crisv32-low.c (the_low_target): Likewise.
	* linux-low.c (delete_lwp): Invoke delete_thread callback if
	set.
	* linux-low.h (struct linux_target_ops) <delete_thread>: New
	field.
	* linux-m32r-low.c (the_low_target): Add thread delete callback.
	* linux-mips-low.c (mips_linux_delete_thread): New function.
	(the_low_target): Add thread delete callback.
	* linux-ppc-low.c (the_low_target): Likewise.
	* linux-s390-low.c (the_low_target): Likewise.
	* linux-sh-low.c (the_low_target): Likewise.
	* linux-tic6x-low.c (the_low_target): Likewise.
	* linux-tile-low.c (the_low_target): Likewise.
	* linux-x86-low.c (the_low_target): Likewise.
	* linux-xtensa-low.c (the_low_target): Likewise.
---
 gdb/aarch64-linux-nat.c           |  1 +
 gdb/arm-linux-nat.c               |  9 +++++++++
 gdb/gdbserver/linux-aarch64-low.c |  1 +
 gdb/gdbserver/linux-arm-low.c     |  9 +++++++++
 gdb/gdbserver/linux-bfin-low.c    |  1 +
 gdb/gdbserver/linux-crisv32-low.c |  1 +
 gdb/gdbserver/linux-low.c         |  7 ++++++-
 gdb/gdbserver/linux-low.h         |  4 ++++
 gdb/gdbserver/linux-m32r-low.c    |  1 +
 gdb/gdbserver/linux-mips-low.c    |  9 +++++++++
 gdb/gdbserver/linux-ppc-low.c     |  1 +
 gdb/gdbserver/linux-s390-low.c    |  1 +
 gdb/gdbserver/linux-sh-low.c      |  1 +
 gdb/gdbserver/linux-tic6x-low.c   |  1 +
 gdb/gdbserver/linux-tile-low.c    |  1 +
 gdb/gdbserver/linux-x86-low.c     |  1 +
 gdb/gdbserver/linux-xtensa-low.c  |  1 +
 gdb/linux-nat.c                   | 21 ++++++++++++++++++++-
 gdb/linux-nat.h                   |  3 +++
 gdb/nat/aarch64-linux.c           |  8 ++++++++
 gdb/nat/aarch64-linux.h           |  3 +++
 gdb/nat/x86-linux.c               |  8 ++++++++
 gdb/nat/x86-linux.h               |  4 ++++
 gdb/s390-linux-nat.c              |  9 +++++++++
 gdb/x86-linux-nat.c               |  1 +
 25 files changed, 105 insertions(+), 2 deletions(-)

diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
index 6ad6f66..4feaec3 100644
--- a/gdb/aarch64-linux-nat.c
+++ b/gdb/aarch64-linux-nat.c
@@ -837,6 +837,7 @@ _initialize_aarch64_linux_nat (void)
   /* Register the target.  */
   linux_nat_add_target (t);
   linux_nat_set_new_thread (t, aarch64_linux_new_thread);
+  linux_nat_set_delete_thread (t, aarch64_linux_delete_thread);
   linux_nat_set_new_fork (t, aarch64_linux_new_fork);
   linux_nat_set_forget_process (t, aarch64_forget_process);
   linux_nat_set_prepare_to_resume (t, aarch64_linux_prepare_to_resume);
diff --git a/gdb/arm-linux-nat.c b/gdb/arm-linux-nat.c
index fc66063..8b25ff7 100644
--- a/gdb/arm-linux-nat.c
+++ b/gdb/arm-linux-nat.c
@@ -1202,6 +1202,14 @@ arm_linux_new_thread (struct lwp_info *lp)
   lp->arch_private = info;
 }
 
+/* Function to call when a thread is being deleted.  */
+
+static void
+arm_linux_delete_thread (struct arch_lwp_info *arch_lwp)
+{
+  xfree (arch_lwp);
+}
+
 /* Called when resuming a thread.
    The hardware debug registers are updated when there is any change.  */
 
@@ -1313,6 +1321,7 @@ _initialize_arm_linux_nat (void)
 
   /* Handle thread creation and exit.  */
   linux_nat_set_new_thread (t, arm_linux_new_thread);
+  linux_nat_set_delete_thread (t, arm_linux_delete_thread);
   linux_nat_set_prepare_to_resume (t, arm_linux_prepare_to_resume);
 
   /* Handle process creation and exit.  */
diff --git a/gdb/gdbserver/linux-aarch64-low.c b/gdb/gdbserver/linux-aarch64-low.c
index 334310b..ed6a993 100644
--- a/gdb/gdbserver/linux-aarch64-low.c
+++ b/gdb/gdbserver/linux-aarch64-low.c
@@ -2991,6 +2991,7 @@ struct linux_target_ops the_low_target =
   aarch64_linux_siginfo_fixup,
   aarch64_linux_new_process,
   aarch64_linux_new_thread,
+  aarch64_linux_delete_thread,
   aarch64_linux_new_fork,
   aarch64_linux_prepare_to_resume,
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-arm-low.c b/gdb/gdbserver/linux-arm-low.c
index 5a3f465..b27c47e 100644
--- a/gdb/gdbserver/linux-arm-low.c
+++ b/gdb/gdbserver/linux-arm-low.c
@@ -655,6 +655,14 @@ arm_new_thread (struct lwp_info *lwp)
   lwp->arch_private = info;
 }
 
+/* Function to call when a thread is being deleted.  */
+
+static void
+arm_delete_thread (struct arch_lwp_info *arch_lwp)
+{
+  xfree (arch_lwp);
+}
+
 static void
 arm_new_fork (struct process_info *parent, struct process_info *child)
 {
@@ -1053,6 +1061,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   arm_new_process,
   arm_new_thread,
+  arm_delete_thread,
   arm_new_fork,
   arm_prepare_to_resume,
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-bfin-low.c b/gdb/gdbserver/linux-bfin-low.c
index d43b05d..175152c 100644
--- a/gdb/gdbserver/linux-bfin-low.c
+++ b/gdb/gdbserver/linux-bfin-low.c
@@ -136,6 +136,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-crisv32-low.c b/gdb/gdbserver/linux-crisv32-low.c
index 5b3888e..7911104 100644
--- a/gdb/gdbserver/linux-crisv32-low.c
+++ b/gdb/gdbserver/linux-crisv32-low.c
@@ -416,6 +416,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index a7859cc..b29749c 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -414,7 +414,12 @@ delete_lwp (struct lwp_info *lwp)
     debug_printf ("deleting %ld\n", lwpid_of (thr));
 
   remove_thread (thr);
-  free (lwp->arch_private);
+
+  if (the_low_target.delete_thread != NULL)
+    the_low_target.delete_thread (lwp->arch_private);
+  else
+    gdb_assert (lwp->arch_private == NULL);
+
   free (lwp);
 }
 
diff --git a/gdb/gdbserver/linux-low.h b/gdb/gdbserver/linux-low.h
index 9106144..a9377b7 100644
--- a/gdb/gdbserver/linux-low.h
+++ b/gdb/gdbserver/linux-low.h
@@ -194,6 +194,10 @@ struct linux_target_ops
      allocate it here.  */
   void (*new_thread) (struct lwp_info *);
 
+  /* Hook to call when a thread is being deleted.  If extra per-thread
+     architecture-specific data is needed, delete it here.  */
+  void (*delete_thread) (struct arch_lwp_info *);
+
   /* Hook to call, if any, when a new fork is attached.  */
   void (*new_fork) (struct process_info *parent, struct process_info *child);
 
diff --git a/gdb/gdbserver/linux-m32r-low.c b/gdb/gdbserver/linux-m32r-low.c
index b3ee11a..b947fa0 100644
--- a/gdb/gdbserver/linux-m32r-low.c
+++ b/gdb/gdbserver/linux-m32r-low.c
@@ -135,6 +135,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-mips-low.c b/gdb/gdbserver/linux-mips-low.c
index b4a83b0..ec26c2a 100644
--- a/gdb/gdbserver/linux-mips-low.c
+++ b/gdb/gdbserver/linux-mips-low.c
@@ -341,6 +341,14 @@ mips_linux_new_thread (struct lwp_info *lwp)
   lwp->arch_private = info;
 }
 
+/* Function to call when a thread is being deleted.  */
+
+static void
+mips_linux_delete_thread (struct arch_lwp_info *arch_lwp)
+{
+  xfree (arch_lwp);
+}
+
 /* Create a new mips_watchpoint and add it to the list.  */
 
 static void
@@ -893,6 +901,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   mips_linux_new_process,
   mips_linux_new_thread,
+  mips_linux_delete_thread,
   mips_linux_new_fork,
   mips_linux_prepare_to_resume
 };
diff --git a/gdb/gdbserver/linux-ppc-low.c b/gdb/gdbserver/linux-ppc-low.c
index 33a9feb..f31a47b 100644
--- a/gdb/gdbserver/linux-ppc-low.c
+++ b/gdb/gdbserver/linux-ppc-low.c
@@ -3125,6 +3125,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-s390-low.c b/gdb/gdbserver/linux-s390-low.c
index f02c2d3..db8c990 100644
--- a/gdb/gdbserver/linux-s390-low.c
+++ b/gdb/gdbserver/linux-s390-low.c
@@ -2768,6 +2768,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-sh-low.c b/gdb/gdbserver/linux-sh-low.c
index ac084c9..273062f 100644
--- a/gdb/gdbserver/linux-sh-low.c
+++ b/gdb/gdbserver/linux-sh-low.c
@@ -165,6 +165,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-tic6x-low.c b/gdb/gdbserver/linux-tic6x-low.c
index 8931d69..8b2a6f3 100644
--- a/gdb/gdbserver/linux-tic6x-low.c
+++ b/gdb/gdbserver/linux-tic6x-low.c
@@ -398,6 +398,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-tile-low.c b/gdb/gdbserver/linux-tile-low.c
index ee1f196..c5b344b 100644
--- a/gdb/gdbserver/linux-tile-low.c
+++ b/gdb/gdbserver/linux-tile-low.c
@@ -197,6 +197,7 @@ struct linux_target_ops the_low_target =
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/gdbserver/linux-x86-low.c b/gdb/gdbserver/linux-x86-low.c
index 844a165..52cec25 100644
--- a/gdb/gdbserver/linux-x86-low.c
+++ b/gdb/gdbserver/linux-x86-low.c
@@ -2880,6 +2880,7 @@ struct linux_target_ops the_low_target =
   x86_siginfo_fixup,
   x86_linux_new_process,
   x86_linux_new_thread,
+  x86_linux_delete_thread,
   x86_linux_new_fork,
   x86_linux_prepare_to_resume,
   x86_linux_process_qsupported,
diff --git a/gdb/gdbserver/linux-xtensa-low.c b/gdb/gdbserver/linux-xtensa-low.c
index 214abdc..5f2566c 100644
--- a/gdb/gdbserver/linux-xtensa-low.c
+++ b/gdb/gdbserver/linux-xtensa-low.c
@@ -289,6 +289,7 @@ struct linux_target_ops the_low_target = {
   NULL, /* siginfo_fixup */
   NULL, /* new_process */
   NULL, /* new_thread */
+  NULL, /* delete_thread */
   NULL, /* new_fork */
   NULL, /* prepare_to_resume */
   NULL, /* process_qsupported */
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 89e0c62..223703d 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -197,6 +197,9 @@ static struct target_ops linux_ops_saved;
 /* The method to call, if any, when a new thread is attached.  */
 static void (*linux_nat_new_thread) (struct lwp_info *);
 
+/* The method to call, if any, when a thread is destroyed.  */
+static void (*linux_nat_delete_thread) (struct arch_lwp_info *);
+
 /* The method to call, if any, when a new fork is attached.  */
 static linux_nat_new_fork_ftype *linux_nat_new_fork;
 
@@ -836,7 +839,12 @@ static int check_ptrace_stopped_lwp_gone (struct lwp_info *lp);
 static void
 lwp_free (struct lwp_info *lp)
 {
-  xfree (lp->arch_private);
+  /* Let the arch specific bits release arch_lwp_info.  */
+  if (linux_nat_delete_thread != NULL)
+    linux_nat_delete_thread (lp->arch_private);
+  else
+    gdb_assert (lp->arch_private == NULL);
+
   xfree (lp);
 }
 
@@ -4870,6 +4878,17 @@ linux_nat_set_new_thread (struct target_ops *t,
   linux_nat_new_thread = new_thread;
 }
 
+/* Register a method to call whenever a new thread is attached.  */
+void
+linux_nat_set_delete_thread (struct target_ops *t,
+			     void (*delete_thread) (struct arch_lwp_info *))
+{
+  /* Save the pointer.  We only support a single registered instance
+     of the GNU/Linux native target, so we do not need to map this to
+     T.  */
+  linux_nat_delete_thread = delete_thread;
+}
+
 /* See declaration in linux-nat.h.  */
 
 void
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index 3378bd6..c002679 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -165,6 +165,9 @@ void linux_nat_add_target (struct target_ops *);
 /* Register a method to call whenever a new thread is attached.  */
 void linux_nat_set_new_thread (struct target_ops *, void (*) (struct lwp_info *));
 
+/* Register a method to call whenever a new thread is deleted.  */
+void linux_nat_set_delete_thread (struct target_ops *,
+				  void (*) (struct arch_lwp_info *));
 
 /* Register a method to call whenever a new fork is attached.  */
 typedef void (linux_nat_new_fork_ftype) (struct lwp_info *parent,
diff --git a/gdb/nat/aarch64-linux.c b/gdb/nat/aarch64-linux.c
index 388eee8..d7abee8 100644
--- a/gdb/nat/aarch64-linux.c
+++ b/gdb/nat/aarch64-linux.c
@@ -84,6 +84,14 @@ aarch64_linux_new_thread (struct lwp_info *lwp)
   lwp_set_arch_private_info (lwp, info);
 }
 
+/* See nat/aarch64-linux.h.  */
+
+void
+aarch64_linux_delete_thread (struct arch_lwp_info *arch_lwp)
+{
+  xfree (arch_lwp);
+}
+
 /* Convert native siginfo FROM to the siginfo in the layout of the
    inferior's architecture TO.  */
 
diff --git a/gdb/nat/aarch64-linux.h b/gdb/nat/aarch64-linux.h
index 191e1c6..db98df4 100644
--- a/gdb/nat/aarch64-linux.h
+++ b/gdb/nat/aarch64-linux.h
@@ -122,6 +122,9 @@ void aarch64_linux_prepare_to_resume (struct lwp_info *lwp);
 
 void aarch64_linux_new_thread (struct lwp_info *lwp);
 
+/* Function to call when a thread is being deleted.  */
+void aarch64_linux_delete_thread (struct arch_lwp_info *arch_lwp);
+
 ps_err_e aarch64_ps_get_thread_area (struct ps_prochandle *ph,
 				       lwpid_t lwpid, int idx, void **base,
 				       int is_64bit_p);
diff --git a/gdb/nat/x86-linux.c b/gdb/nat/x86-linux.c
index b499e74..fc68106 100644
--- a/gdb/nat/x86-linux.c
+++ b/gdb/nat/x86-linux.c
@@ -68,6 +68,14 @@ x86_linux_new_thread (struct lwp_info *lwp)
 /* See nat/x86-linux.h.  */
 
 void
+x86_linux_delete_thread (struct arch_lwp_info *arch_lwp)
+{
+  xfree (arch_lwp);
+}
+
+/* See nat/x86-linux.h.  */
+
+void
 x86_linux_prepare_to_resume (struct lwp_info *lwp)
 {
   x86_linux_update_debug_registers (lwp);
diff --git a/gdb/nat/x86-linux.h b/gdb/nat/x86-linux.h
index 1b7fee4..493c722 100644
--- a/gdb/nat/x86-linux.h
+++ b/gdb/nat/x86-linux.h
@@ -39,6 +39,10 @@ extern int lwp_debug_registers_changed (struct lwp_info *lwp);
 
 extern void x86_linux_new_thread (struct lwp_info *lwp);
 
+/* Function to call when a thread is being deleted.  */
+
+extern void x86_linux_delete_thread (struct arch_lwp_info *arch_lwp);
+
 /* Function to call prior to resuming a thread.  */
 
 extern void x86_linux_prepare_to_resume (struct lwp_info *lwp);
diff --git a/gdb/s390-linux-nat.c b/gdb/s390-linux-nat.c
index b395529..22c0232 100644
--- a/gdb/s390-linux-nat.c
+++ b/gdb/s390-linux-nat.c
@@ -776,6 +776,14 @@ s390_new_thread (struct lwp_info *lp)
   s390_mark_per_info_changed (lp);
 }
 
+/* Function to call when a thread is being deleted.  */
+
+static void
+s390_delete_thread (struct arch_lwp_info *arch_lwp)
+{
+  xfree (arch_lwp);
+}
+
 /* Iterator callback for s390_refresh_per_info.  */
 
 static int
@@ -1031,6 +1039,7 @@ _initialize_s390_nat (void)
   /* Register the target.  */
   linux_nat_add_target (t);
   linux_nat_set_new_thread (t, s390_new_thread);
+  linux_nat_set_delete_thread (t, s390_delete_thread);
   linux_nat_set_prepare_to_resume (t, s390_prepare_to_resume);
   linux_nat_set_forget_process (t, s390_forget_process);
   linux_nat_set_new_fork (t, s390_linux_new_fork);
diff --git a/gdb/x86-linux-nat.c b/gdb/x86-linux-nat.c
index 4611527..ce56c2e 100644
--- a/gdb/x86-linux-nat.c
+++ b/gdb/x86-linux-nat.c
@@ -354,6 +354,7 @@ x86_linux_add_target (struct target_ops *t)
 {
   linux_nat_add_target (t);
   linux_nat_set_new_thread (t, x86_linux_new_thread);
+  linux_nat_set_delete_thread (t, x86_linux_delete_thread);
   linux_nat_set_new_fork (t, x86_linux_new_fork);
   linux_nat_set_forget_process (t, x86_forget_process);
   linux_nat_set_prepare_to_resume (t, x86_linux_prepare_to_resume);
-- 
2.7.4