On Jul 14, 2011, at 10:39 AM, Joerg Sonnenberger wrote:
> On Thu, Jul 14, 2011 at 10:28:52AM -0700, Ted Kremenek wrote:
>> Hi Kaelyn,
>>
>> I was reviewing this patch (which I think is a great step), and I had a
>> high-level comment about the following test case:
>>
>> +void swallow (const char *x) { (void)x; }
>> +void test_pointer_arithmetic() {
>> + const char hello[] = "Hello world!"; // expected-note 2 {{declared here}}
>> + const char *helloptr = hello;
>> +
>> + swallow("Hello world!" + 6); // no-warning
>> + swallow("Hello world!" - 6); // expected-warning {{refers before the
>> beginning of the array}}
>> + swallow("Hello world!" + 14); // expected-warning {{refers past the end
>> of the array}}
>>
>> Do we really want this to be a warning? There are plenty of examples where
>> an out-of-bounds pointer is computed for legit reasons. As long as that
>> address is not dereferenced, there isn't necessarily a problem. I'm fearful
>> this may generate a fair amount of noise on codebases that do elaborate
>> tricks with pointer offsets. Indeed this very example doesn't actually
>> exhibit a "bug".
>
> I'm not sure yet, but I think this is something that really should be
> investigated on real code bases first (and it should be a separate
> option for that reason).
Years ago one example I saw was the "Numerical Recipes" library, which tried to
turn all C one-dimensional arrays into arrays with a "base index" of 1 (to be
amendable for scientists previously coding with Fortran). I'm not arguing that
this is a good idea, but on that example this warning would likely fire
thousands of times.
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