[sanitizer] Add GetMaxVirtualAddress() support for LoongArch

[tangyouling]

Summary

Add support for getting the maximum virtual address, LoongArch has multiple
address space layouts, the default maximum virtual address of the current
user space is 47 bits. (from TASK_SIZE in the kernel for loongarch64).

[xen0n]

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

1118

I believe you could just add defined(__loongarch__) to the case above and adjust the comments. LoongArch is also an architecture with multiple address space layouts possible.

[tangyouling]

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

1118

I believe you could just add defined(__loongarch__) to the case above and adjust the comments. LoongArch is also an architecture with multiple address space layouts possible.

Yes, of course, I will adjust it. Initially just wanted to be consistent with asan_mapping.h (asan only supports 47 bit in loongarch64 for now).

[tangyouling]

Address @xen0n's comments.

[SixWeining]

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

1118

Can this approach applies to
https://reviews.llvm.org/D129418#inline-1243719
https://reviews.llvm.org/D137013#inline-1321523
to support multiple layouts?

[tangyouling]

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

1118

Can this approach applies to
https://reviews.llvm.org/D129418#inline-1243719
https://reviews.llvm.org/D137013#inline-1321523
to support multiple layouts?

Current asan only supports 47-bit address space layout.

[SixWeining]

LGTM. But better to wait for others.

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

# if defined(__powerpc64__) || defined(__aarch64__)
   // 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.
   // Similarly, aarch64 has multiple address space layouts: 39, 42 and 47-bit.
   return (1ULL << (MostSignificantSetBitIndex(GET_CURRENT_FRAME()) + 1)) - 1;
+#elif SANITIZER_LOONGARCH64
+  return (1ULL << 47) - 1;  // 0x00007fffffffffffUL
 #elif SANITIZER_RISCV64
   return (1ULL << 38) - 1;
 # elif SANITIZER_MIPS64
   return (1ULL << 40) - 1;  // 0x000000ffffffffffUL;
 # elif defined(__s390x__)
   return (1ULL << 53) - 1;  // 0x001fffffffffffffUL;
 #elif defined(__sparc__)
   return ~(uptr)0;