[sanitizer] Warn if allocator size exceeds max user virtual address (llvm#152428)

This warns the user of incompatible configurations, such as 39-bit and
42-bit VMAs for AArch64 non-Android Linux ASan
(llvm#145259).

Author: thurstond

compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary64.h

@@ -113,6 +113,24 @@ class SizeClassAllocator64 {
   // ~(uptr)0.
   void Init(s32 release_to_os_interval_ms, uptr heap_start = 0) {
     uptr TotalSpaceSize = kSpaceSize + AdditionalSize();
+
+    uptr MaxAddr = GetMaxUserVirtualAddress();
+    // VReport does not call the sanitizer allocator.
+    VReport(3, "Max user virtual address: 0x%zx\n", MaxAddr);
+    VReport(3, "Total space size for primary allocator: 0x%zx\n",
+            TotalSpaceSize);
+    // TODO: revise the check if we ever configure sanitizers to deliberately
+    //       map beyond the 2**48 barrier (note that Linux pretends the VMA is
+    //       limited to 48-bit for backwards compatibility, but allows apps to
+    //       explicitly specify an address beyond that).
+    if (heap_start + TotalSpaceSize >= MaxAddr) {
+      // We can't easily adjust the requested heap size, because kSpaceSize is
+      // const (for optimization) and used throughout the code.
+      VReport(0, "Error: heap size %zx exceeds max user virtual address %zx\n",
+              TotalSpaceSize, MaxAddr);
+      VReport(
+          0, "Try using a kernel that allows a larger virtual address space\n");
+    }
     PremappedHeap = heap_start != 0;
     if (PremappedHeap) {
       CHECK(!kUsingConstantSpaceBeg);