[PATCH] jffs, clang: avoid some warnings of used uninitialized ptr

[Sebastian Huber]

On 05/10/2018 09:25, Daniel Hellstrom wrote:
> On 2018-10-05 09:12, Sebastian Huber wrote:
>> On 05/10/2018 08:57, Daniel Hellstrom wrote:
>>> This fixes the following test failures on LEON3 UP/SMP when
>>> built using clang compiler:
>>>   * fsjffs2gc01
>>>   * jffs2_fserror
>>>   * jffs2_fspermission
>>>   * jffs2_fsrdwr
>>>   * jffs2_fstime
>>
>> The problem is probably in the 
>> rbtree_postorder_for_each_entry_safe(). Coverity Scan has also an 
>> issue with this macro. It is on my todo list. Please do not check in 
>> this patch.
> Ok I will not push it. Yes I was also thinking so. To use offsetof() 
> macro could be an option maybe, however the node type input is not 
> known to the rbtree_postorder_for_each_entry_safe() function even 
> though it only used from jffs2 code. 

The Linux code uses typeof. We could do this also:

diff --git a/cpukit/include/linux/rbtree.h b/cpukit/include/linux/rbtree.h
index 53c777e8c1..8fc575240f 100644
--- a/cpukit/include/linux/rbtree.h
+++ b/cpukit/include/linux/rbtree.h
@@ -126,12 +126,12 @@ static inline struct rb_node *rb_parent( struct 
rb_node *node )
    for ( \
      node = _RBTree_Postorder_first( \
        (RBTree_Control *) root, \
-      (size_t) ( (char *) &node->field - (char *) node ) \
+      offsetof( __typeof__( *node ), field ) \
      ); \
      node != NULL && ( \
        next = _RBTree_Postorder_next( \
          &node->field, \
-        (size_t) ( (char *) &node->field - (char *) node ) \
+        offsetof( __typeof__( *node ), field ) \
        ), \
        node != NULL \
      ); \

It shouldn't be a big problem since at least GCC and clang supports it. 
It is also a standard C++ operator. It is already used in

cpukit/libfs/src/jffs2/include/linux/list.h

-- 
Sebastian Huber, embedded brains GmbH

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