Re: (ITS#8988) Undefined Behavior in slapadd

[hyc@symas.com]

hyc@symas.com wrote:
> Jeffrey Walton wrote:
>> On Fri, Jun 7, 2019 at 10:08 AM Howard Chu <hyc@symas.com> wrote:
>>>
>>> Jeffrey Walton wrote:
>>>> On Fri, Jun 7, 2019 at 9:59 AM Howard Chu <hyc@symas.com> wrote:
>>>>>
>>>>> noloader@gmail.com wrote:
>>>>>> On Fri, Jun 7, 2019 at 9:32 AM Howard Chu <hyc@symas.com> wrote:
>>>>>>>
>>>>>>> noloader@gmail.com wrote:
>>>>>>> ...
>>>>>>>> I encourage OpenLDAP to fix the undefined behavior. OpenLDAP is an
>>>>>>>> important project, and the undefined behavior is causing too many
>>>>>>>> tangential problems.
>>>>>>>
>>>>>>> Undefined behavior is not a bug, nor is it prohibited by the C spec. It is a necessary
>>>>>>> part of the language for its intended use as a system programming language, writing
>>>>>>> machine-specific programs. Anyone who says it is prohibited by the spec is wrong.
>>>>>>
>>>>>> I don't believe this is correct.
>>>>>>
>>>>>> Maybe you are thinking of implementation defined behavior?
>>>>>
>>>>> That would apply to how a particular compiler implementation treats some piece of code.
>>>>> Whether a CPU supports unaligned access is machine-defined. Since our code is already
>>>>> properly ifdef'd for the machines which do or don't support it, the fact that this is
>>>>> "non-portable" is not an issue.
>>>>
>>>> The undefined behavior is causing OpenLDAP to fail testing.
>>>>
>>>> Worse, it is causing test failures in programs and libraries which use
>>>> OpenLDAP. The OpenLDAP bugs have cross-pollinated into other programs
>>>> and libraries. It is not simply contained or limited to OpenLDAP.
>>>>
>>>> That's a big problem for testing a QA folks.
>>>
>>> Then the tests are broken, because these are not bugs.
>>
>> They are absolutely OpenLDAP bugs. The unaligned accesses are
>> Undefined Behavior.
> 
> Simply because the C standard doesn't specify what the behavior is doesn't make it a bug.
> It would be unreasonable to expect the standards body to exhaustively list all of the
> possible behaviors on all of the possible hardware architectures that the language is
> implemented for. Leaving it undefined in the spec only means they chose not to specify
> a behavior. That means the actual behavior depends on the underlying machine. On the
> x86 family the behavior is well defined.

Also note: Behaviors are left undefined when they are non-portable. But being non-portable
isn't illegal in C. The entire purpose of conditional compilation is to support non-portable
code.

-- 
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/