Re: [Libvir] Windows sizeof(long) != Linux sizeof(long)
On Wed, Jan 23, 2008 at 12:33:47AM +0000, Daniel P. Berrange wrote:
Just discovered that on x86_64, Windows and Linux differ in what
they
think sizeof(long) to be.
http://lists.xensource.com/archives/html/xen-devel/2008-01/msg00736.html
http://www.winehq.org/pipermail/wine-devel/2005-July/038602.html
Windows i686: sizeof(long) == 4, sizeof(void*) == 4
Windows x86_64: sizeof(long) == 4, sizeof(void*) == 8
Linux i686: sizeof(long) == 4, sizeof(void*) == 4
Linux x86_64: sizeof(long) == 8, sizeof(void*) == 8
Unfortunately we have a number of APIs which use 'long' in the public header
file for dealing with VM memory. Fortunately they are all using memory in
size of KB, so we are not totally doomed until people start wanting to
manage VMs with > 2 TB of RAM. Also fortunately, the wire-encoding for
these APIs all uses hyper, so on the wire everything is 64-bit guarenteed.
Eventually though we might want to consider adding
struct virDomainInfo64
struct virNodeInfo64
virDomainGetMemory64
virDomainSetMemory64
virDomainSetMaxMemory64
Another option is totry to fix things in the current API.
Can we define a type which is an integer guaranteed to be of the expected
type on the existing platforms (basically Linux/BSD/Solaris) and for which
we can make sure the exact same size will be used on new platforms when
added ?
....simply replacing 'long' with 'long long' in these
5 APIs so we have
public APIs whose precision matches the wire encoding.
This may be cleaner than adding 2 new data structures and 3 new entry points
just for compatibility with 32 bits.
If we actually duplicate, then as Rich suggested let's go for fixed size
integer definitions like uint64 and the likes, to not get into more troubles
later. Oh and mark the old structures and entry points as deprecated in the
documentation, make sure the python/perl/java/etc. bindings use the new ones,
and that all existing examples/virsh and docs are updated to the new ones.
More immediately though, we need to be careful that there is no code
that
assumes sizeof(long) == sizeof(void*) - eg any places we cast pointers
to integers and back again will break on Windows 64. Again fortunately, so
far I can only find places going from int -> pointer -> int which is OK
because we're not loosing precision.
I don't think we would do this conciously in any C code but we should
check the protocol and bindings generators (I think it is okay but better
check again).
Damn ...
Daniel
--
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Daniel Veillard | virtualization library http://libvirt.org/
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