Sept 11 with tools and tests removed

[Henri Verbeet]

2009/9/13 Ben Klein <shacklein at gmail.com>:
> 2009/9/13 Nicolas Le Cam <niko.lecam at gmail.com>:
>> Last one is also a false positive, it's just two pointers being
>> subtracted to retrieve an offset.
>
> That's not the reason why it's a false positive. Without context that
> line does look like a NULL-dereference (dmW is dereferenced to get the
> first pointer before any NULL checking). However it's in a static
> function that is called in two places, both of which already check the
> pointer being dereferenced.
>
No, that's not how it works. The expression "dmW->dmFormName" by
itself doesn't dereference anything, it's just an address. Only once
you read or write something from/to that address does dmW being NULL
(or otherwise invalid) become a problem. Here we just subtract "dmW"
from that address to get the field offset of "dmFormName" in the
DEVMODEW structure. Note that the value of "off_formname" doesn't
depend on the value of "dmW", just on its type. The compiler will
probably recognize that and optimize it away. Arguably the code in
question should just use the FIELD_OFFSET macro though.