Hi Andre,

Well,  there is no bug here.
You try to mmap some memory and request the kernel to provide a specific 
virtual address. Unfortunately, the virtual address you request is not 
available in your process address space. So fortunately, the kernel provides 
you a replacement address that is valid. Requesting a specific virtual address 
through mmap is a 'best effort' tentative that may fail if the address is not 
available, in which case another valid address is returned. You can ask mmap to 
fail in case the virtual address you request is not available if you prefer.
But from a general perspective, it is not advised to request a specific virtual 
address, or at least a user space shall no rely on fixed virtual address.

As you could notice, depending on the user-space implementation and
architecture, the mmapping of libraries can be done at various virtual
addresses by default. It appears that with the Ubuntu FS, the address
your script tries to access is not free because used by some libraries
or other mmaped files.

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https://bugs.launchpad.net/bugs/697004

Title:
  mmap for fixed address fails for higher addresses

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