Re: (ITS#8988) Undefined Behavior in slapadd

[hyc@symas.com]

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.

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