[Bug sanitizer/64435] [5 Regression] Bootstrap failure in libsanitizer on AArch64 with Linux kernel <= 3.15

["clyon at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64435

--- Comment #20 from clyon at gcc dot gnu.org ---
(In reply to Jakub Jelinek from comment #14)
> 
> https://github.com/torvalds/linux/blob/master/arch/arm64/include/asm/memory.h
> https://github.com/torvalds/linux/blob/master/arch/arm64/Kconfig
> reveals that aarch64 can be on Linux configured to support 39, 42 or 48 bits
> virtual address space.  The current libsanitizer/asan/ and
> gcc/config/aarch64/aarch64.c (aarch64_asan_shadow_offset) seems to be okay
> only for the 39 bits virtual address space, while Fedora/RHEL apparently use
> 42 bits VA.  Wonder if aarch64 couldn't use a layout closer to what x86_64
> uses for asan, with shadow offset low 0x7fff8000, which is flexible to
> different sizes of the virtual address space.

Thanks for pointing that, I wasn't aware of it when I worked on the initial
port. My platform had 39 bits virtual address space, and I didn't notice there
were other possibilities.