Problems with VirtualAlloc/Lock

Michael Ost most at
Tue Mar 15 15:12:42 CST 2005

On Tue, 2005-03-15 at 11:12, Alexandre Julliard wrote:
> Michael Ost <most at> writes:
> > On Tue, 2005-03-15 at 01:09, Alexandre Julliard wrote:
> > > That's a kernel limitation. If you hack the kernel to start allocating
> > > from lower addresses (or implement the syscall we discussed to let us
> > > specify the mmap range) you can get the full 2GB.
> > 
> > Could you point me to the kernel limitation? I can mmap() 2GB on an
> > unhacked 2.4.19 kernel with this loop:
> That's because you can mmap above 0x8000000, but that's not allowed
> under Windows. You'll note that on a standard kernel you can only mmap
> 2GB even though you have a 3GB address space.  If you set the large
> address flag when building your application you will get a 3GB address
> space on Wine too, which will then let you allocate 2GB; but the
> resulting high addresses may break your plugins. The real problem is
> that the kernel starts allocations at 0x40000000.

What's involved in doing such a hack/syscall? Are there any patches that
make this change lying around somewhere that I could look at?

Wine reports that apps have 2GB of VM in GlobalMemoryStatus, but they
actually only have 1GB. Isn't that a Wine bug?

To summarize and make sure I understand: the problem is that Linux and
Windows allocate VM from different address ranges. While both can alloc
2GB, the intersection of addresses is only 1GB --- between 0x40000000
and 0x80000000. 

On Windows (based on the MSDN docs) VM is allocated from 0x00000010 to
0x80000000. On Linux (unhacked 2.4 kernel), mmap runs from 0x40000000 to

Thanks... mo

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