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Re: 64 bit addressing (fixed)

On Saturday, June 28, 2003, at 03:10 PM, Chris Kane wrote:

> On Saturday, June 28, 2003, at 11:08, Mike Vannorsdel wrote:
>
>> Then it sounds like most of Mac OS X will remain 32-bit except for
>> special cases (apps which need the large allocations). It seems like
>> making the libraries 64-bit will cause huge backwards compatibility
>> problems. Unless there are 32 and 64-bit versions of each.
>
> I assume there will need to be an entire stack of libraries for 32 and
> another for 64 bit, with no mix-n-matching.
>
>> What would happen if your 32-bit code linked with a 64-bit lib?
>
> I assume that the upper 32 bits in the general purpose registers in a
> 32-bit task would always be zeros, since the task wouldn't be putting
> anything in there itself. However, if the library tried to return
> something > 32 bits, the 32 bit task won't see the value properly in
> some way or other. Or, if a pointer to a pointer was being passed in,
> the 64-bit library might put a 64-bit pointer in the space for a
> 32-bit pointer that the app is passing a reference to. It's all just
> trouble waiting to happen.

i had the opportunity to talk about this issue with jim magee at the
campus beer bash :-) so i've been thinking about this for a couple
days. having an entire stack of libraries for both 32 and 64 bit code
seems ineffiecient. a good solution might be:

a) provide new 64 bit allocators vm_allocate64(), malloc64()...etc,
this way any buffers created by the old allocators can be guaranteed to
be in the 32 bit space; and would fail if 32 bit space was full.

b) provide one set of 64bit clean system libraries across the board for
jaguar64; however, the libraries only use the 32 bit allocators
internally. this way 32 bit pointers going into a library will
obviously work, libraries will only create, copy and return to 32 bit
space, and a 64 bit pointer passed into a library will either round
trip cleanly, or get copied and returned into 32 bit space for any api
that copies the data.

my initial response was somehow cutoff here:

the basic idea was that as long as all addresses were passed into the
libraries in 64 bit registers (and the libs are 64 clean), then even
corner cases like passing in a pointer to a pointer should still work,
because that should simply pass through. and as long as the libraries
are only allocating data in the 32 bit space (or passing through).
returning pointers to pointers would work fine as well, as it will
either be 32 bit values in 64 registers, or something that passed
through.
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References: 
 >Re: 64 bit addressing (From: Chris Kane <email@hidden>)



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