strnlen_s with const string not working with smax > string size + 1

[INgoRah]

When we use the strnlen_s() function it calls _strnlen_s_chk(str,smax,BOS(str)).
BOS(str) will result in the length of the buffer if the compiler can estimate it:
# define BOS(dest) __builtin_object_size((dest),1)

In _strnlen_s_chk() there is a this check:

	if (unlikely(smax > strbos)) {
		......
		return 0;
	}

If the given buffer length (smax) is bigger than the buffer size calculated by the compiler (strbos) it returns 0 and gives a warning.
The test suite does not include some standard cases to cover this, so it passes.
But a simple test like this would fail (would be nice in tests\test_strnlen_s.c:9

    max_len = 9;
    len = strnlen_s ("testing", max_len);

    if (len != 7) {
        printf("%s %u   len=%u  \n",
                     __FUNCTION__, __LINE__, (unsigned)len);
        errs++;
    }

That means: you need to know the string size to get the string size!

[rurban]

Uh, that's awfully wrong logic indeed. strnlen_s should not fail when the actual length is smaller than the maxlen. smax should only limit scanning on overlong strings, when there's still no 0. I have to check the specs on this. Does not make sense at all like this.