Re: C programming on ARM


"Hans-Bernhard Bröker" <HBBroeker@xxxxxxxxxxx> wrote in message news:fnr0vs$mp6$00$1@xxxxxxxxxxxxxxxxxxxx
Wilco Dijkstra wrote:

With any byte addressable architecture, a pointer is just a pointer.

But there are quite a few non-byte addressable architectures out there.
Including ARM, last I checked.

Actually most architectures are byte addressable, including ARM,

Depends on what exactly you mean by the term.

AFAIK ARM7 is byte-addressable only for bytes, but not for larger objects. Well, may be it's just me, but I wouldn't
call what happens when an ARM7 accesses a 32-bit integer without 4-byte alignment "addressing".

Obviously not all possible pointer values are valid for all types. This doesn't
affect byte addressability as casting between char* and int* doesn't lose
information. Accessing a misaligned pointer will result in an exception
(which is a good way to detect corrupted pointers). However if you use
the correct type (eg. __packed int *p rather than int *p), the compiler will
generate an unaligned access.

Similarly a 32-bit CPU with less than 4GB of memory doesn't have
(say) a 18.25-bit address space - it still has a 32-bit address space of
which only a small proportion is valid.

Wilco



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