Hmm. It depends on your interpretation of "representation".
On memory a null pointer can have some bit set.
No, see a very recent discussion on austin group list
(which list also few machines that don't have all 0-bits null pointer)
To clarify, from Rationale of C99, section 6.7.8 "Initialization":
: An implementation might conceivably have codes for floating zero
: and/or null pointer other than all bits zero. In such a case,
: the implementation must fill out an incomplete initializer with
: the various appropriate representations of zero; it may not just
: fill the area with zero bytes. As far as the committee knows,
: all machines treat all bits zero as a representation of
: floating-point zero. But, all bits zero might not be the
: canonical representation of zero.
Anyway, I think for kernel it is safe to assume all-zero bit
null pointer.
ciao
cate
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