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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug sanitizer/64435] [5 Regression] Bootstrap failure in libsanitizer on AArch64 with Linux kernel <= 3.15
Date: Mon, 19 Jan 2015 18:01:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64435

--- Comment #17 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
PPC64 actually supports both 44 and 46 bit address space:

uptr GetMaxVirtualAddress() {
#if SANITIZER_WORDSIZE == 64
# if defined(__powerpc64__)
  // On PowerPC64 we have two different address space layouts: 44- and 46-bit.
  // We somehow need to figure out which one we are using now and choose
  // one of 0x00000fffffffffffUL and 0x00003fffffffffffUL.
  // Note that with 'ulimit -s unlimited' the stack is moved away from the top
  // of the address space, so simply checking the stack address is not enough.
  // This should (does) work for both PowerPC64 Endian modes.
  return (1ULL << (MostSignificantSetBitIndex(GET_CURRENT_FRAME()) + 1)) - 1;
# elif defined(__aarch64__)
  return (1ULL << 39) - 1;
# elif defined(__mips64)
  return (1ULL << 40) - 1;
# else
  return (1ULL << 47) - 1;  // 0x00007fffffffffffUL;
# endif
#else  // SANITIZER_WORDSIZE == 32
  uptr res = (1ULL << 32) - 1;  // 0xffffffff;
  if (!common_flags()->full_address_space)
    res -= GetKernelAreaSize();
  CHECK_LT(reinterpret_cast<uptr>(&res), res);
  return res;
#endif  // SANITIZER_WORDSIZE
}

it is just that aarch64 hardcodes this right now.  Suppose doing something like
ppc64 does could work.