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Re: [PATCH] -Warray-bounds TLC


On Apr 17, 2015, at 1:52 PM, Steve Ellcey <sellcey@imgtec.com> wrote:
>  struct link_namespaces *ns = &_dl_ns[nsid];
>  (nsid != 0) ? (void) (0) : bad ("nsid != 0”);

Without disagreeing with the fact this looks like a bug, ideally, the two lines above would be switched:

c++98:
  If both the pointer operand and the result point to  elements
  of  the  same  array object, or one past the last element of the array
  object, the evaluation shall not produce an overflow;  otherwise,  the
  behavior is undefined.

and c99 tc3:
8   When an expression that has integer type is added to or subtracted from a pointer, the
    result has the type of the pointer operand. If the pointer operand points to an element of
    an array object, and the array is large enough, the result points to an element offset from
    the original element such that the difference of the subscripts of the resulting and original
    array elements equals the integer expression. In other words, if the expression P points to
    the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and
    (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of
    the array object, provided they exist. Moreover, if the expression P points to the last
    element of an array object, the expression (P)+1 points one past the last element of the
    array object, and if the expression Q points one past the last element of an array object,
    the expression (Q)-1 points to the last element of the array object. If both the pointer
    operand and the result point to elements of the same array object, or one past the last
    element of the array object, the evaluation shall not produce an overflow; otherwise, the
    behavior is undefined.

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