cppcheck sept 18 redux

[Mike Kaplinskiy]

On Tue, Sep 22, 2009 at 3:06 AM, Ben Klein <shacklein at gmail.com> wrote:
> 2009/9/22 Mike Kaplinskiy <mike.kaplinskiy at gmail.com>:
>> On Tue, Sep 22, 2009 at 1:09 AM, Vitaliy Margolen
>> <wine-devel at kievinfo.com> wrote:
>>>> [/home/cahrendt/wine-git/dlls/wineps.drv/init.c:270]: (error) Possible
>>>> null pointer dereference: dmW - otherwise it is redundant to check if
>>>> dmW is null at line 272
>>>
>>> This is a real bug and should be fixed:
>>>>     ptrdiff_t off_formname = (const char *)dmW->dmFormName - (const char *)dmW;
>>> Does indeed dereference dmW to get the value of dmFormName.
>>
>> It actually doesn't, it's a tricky case where dmW->dwFormName ==
>> &dmW->dwFormName, because dwFormName is an array allocated as part of
>> the struct. I made that mistake too the previous cppcheck round.
>
> I thought I'd covered this before. It's complaining about dmW not
> being validated before dmW->dmFormName (which de-references dmW to get
> at its dmFormName member). In current code, it's not a problem because
> dmW is validated before it's run in both cases (lines 369 and 403). It
> is right about the redundant test NULL check on 272 though; if dmW is
> NULL, the function will segfault.
>

It actually does not dereference anything. Try passing null into the
function - it will work just fine. This is a special case because the
array isn't dynamically allocated but is part of the struct, which
means that dmW->dmFormName == (dmW+__offset of dmFormName) and not
*(dmW+__offset of dmFormName). You can try writing a test program
yourself - it will run just fine.

Mike.