On 05/10/2018 01:26 PM, Martin Sebor wrote:
GCC 8.1 warns for unbounded (and some bounded) string comparisons
involving arrays declared attribute nonstring (i.e., char arrays
that need not be nul-terminated).  For instance:

  extern __attribute__((nonstring)) char a[4];

  int f (void)
    return strncmp (a, "123", sizeof a);

  warning: ‘strcmp’ argument 1 declared attribute ‘nonstring’

Note that the warning refers to strcmp even though the call in
the source is to strncmp, because prior passes transform one to
the other.

The warning above is unnecessary (for strcmp) and incorrect for
strncmp because the call reads exactly four bytes from the non-
string array a regardless of the bound and so there is no risk
that it will read past the end of the array.

The attached change enhances the warning to use the length of
the string argument to suppress some of these needless warnings
for both bounded and unbounded string comparison functions.
When the length of the string is unknown, the warning uses its
size (when possible) as the upper bound on the number of accessed
bytes.  The change adds no new warnings.

I'm looking for approval to commit it to both trunk and 8-branch.


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