_Chain_Is_first/last overshoot

[Sébastien Bourdeauducq]

-------- Original Message --------
Subject: [Milkymist-devel] [PATCH, tentative] RTEMS: 
_Chain_Is_first/last overshoot
Date: Wed, 9 Nov 2011 16:53:53 -0300
From: Werner Almesberger <werner at almesberger.net>
Reply-To: Milkymist One, Milkymist SoC and Flickernoise developers' list 
<devel at lists.milkymist.org>
To: Milkymist One, Milkymist SoC and Flickernoise developers' list 
<devel at lists.milkymist.org>

Doubly-linked lists ("chains") in RTEMS have a "control" block that
looks like the next/prev link pair in an element. The list elements
link both ways to this control block.

_Chain_Is_first and _Chain_Is_last only probed if the link to the
next element - which would be the control block - is non-NULL.
Telling by the function description and given that there are already
functions called _Chain_Is_head and _Chain_Is_tail (which could be
simplified), this is probably not the intended behaviour.

This also affects the aliases rtems_chain_is_first and
rtems_chain_is_last.

These functions are not used a lot and I haven't seen any immediate
effect on M1 after changing them, so I can't say whether this patch
may unearth other problems.

- Werner

Index: cpukit/score/inline/rtems/score/chain.inl
===================================================================
RCS file: /usr1/CVS/rtems/cpukit/score/inline/rtems/score/chain.inl,v
retrieving revision 1.23
diff -U 4 -r1.23 chain.inl
--- cpukit/score/inline/rtems/score/chain.inl	25 Nov 2010 11:48:11 
-0000	1.23
+++ cpukit/score/inline/rtems/score/chain.inl	9 Nov 2011 19:42:13 -0000
@@ -296,9 +296,9 @@
  RTEMS_INLINE_ROUTINE bool _Chain_Is_first(
    const Chain_Node *the_node
  )
  {
-  return (the_node->previous == NULL);
+  return the_node->previous->previous == NULL;
  }

  /** @brief Is this the Last Node on the Chain
   *
@@ -313,9 +313,9 @@
  RTEMS_INLINE_ROUTINE bool _Chain_Is_last(
    const Chain_Node *the_node
  )
  {
-  return (the_node->next == NULL);
+  return the_node->next->next == NULL;
  }

  /** @brief Does this Chain have only One Node
   *
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