[Qemu-arm] AArch64 memory layout

[Yury Usishchev]

Hello!

I found that address space for AArch64 is considered to be 64bit:

target-arm/cpu.h:1776:
#if defined(TARGET_AARCH64)
#  define TARGET_PHYS_ADDR_SPACE_BITS 48
#  define TARGET_VIRT_ADDR_SPACE_BITS 64
#else
#  define TARGET_PHYS_ADDR_SPACE_BITS 40
#  define TARGET_VIRT_ADDR_SPACE_BITS 32
#endif

But from kernel side it is either 39 or 42 or 48 bit:
https://www.kernel.org/doc/Documentation/arm64/memory.txt

This causes problems with address sanitizer usage under qemu. ASAN under qemu 
detects address space as 39 bits. When
host mmap returns value over 1<<39 (this can happen on x86_64) ASAN causes 
segmentation fault.

If TARGET_VIRT_ADDR_SPACE_BITS is changed to 39, runtime checks prevents 
mapping from bigger addresses and everything is
fine. But this is not a correct solution as mappings can be also 42 or 48.

So the question is should TARGET_VIRT_ADDR_SPACE_BITS be changed and how?

BR,
Yury Usishchev