Index: clang/lib/AST/ASTContext.cpp
===================================================================
--- clang/lib/AST/ASTContext.cpp
+++ clang/lib/AST/ASTContext.cpp
@@ -72,6 +72,7 @@
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -81,6 +82,7 @@
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>
@@ -826,13 +828,27 @@
   llvm_unreachable("getAddressSpaceMapMangling() doesn't cover anything.");
 }
 
+static std::vector<std::string>
+getRealPaths(llvm::vfs::FileSystem &VFS, llvm::ArrayRef<std::string> Paths) {
+  std::vector<std::string> Result;
+  llvm::SmallString<128> Buffer;
+  for (const auto &File : Paths) {
+    VFS.getRealPath(File, Buffer);
+    Result.push_back(Buffer.str());
+  }
+  return Result;
+}
+
 ASTContext::ASTContext(LangOptions &LOpts, SourceManager &SM,
                        IdentifierTable &idents, SelectorTable &sels,
                        Builtin::Context &builtins)
     : FunctionProtoTypes(this_()), TemplateSpecializationTypes(this_()),
       DependentTemplateSpecializationTypes(this_()),
       SubstTemplateTemplateParmPacks(this_()), SourceMgr(SM), LangOpts(LOpts),
-      SanitizerBL(new SanitizerBlacklist(LangOpts.SanitizerBlacklistFiles, SM)),
+      SanitizerBL(new SanitizerBlacklist(
+          getRealPaths(SM.getFileManager().getVirtualFileSystem(),
+                       LangOpts.SanitizerBlacklistFiles),
+          SM)),
       XRayFilter(new XRayFunctionFilter(LangOpts.XRayAlwaysInstrumentFiles,
                                         LangOpts.XRayNeverInstrumentFiles,
                                         LangOpts.XRayAttrListFiles, SM)),
Index: clang/test/CodeGen/Inputs/sanitizer-blacklist-vfsoverlay.yaml
===================================================================
--- /dev/null
+++ clang/test/CodeGen/Inputs/sanitizer-blacklist-vfsoverlay.yaml
@@ -0,0 +1,12 @@
+{
+  'version': 0,
+  'roots': [
+    { 'name': 'DIR', 'type': 'directory',
+      'contents': [
+        { 'name': 'only-virtual-file.blacklist', 'type': 'file',
+          'external-contents': 'REAL_FILE'
+        }
+      ]
+    }
+  ]
+}
Index: clang/test/CodeGen/ubsan-blacklist.c
===================================================================
--- clang/test/CodeGen/ubsan-blacklist.c
+++ clang/test/CodeGen/ubsan-blacklist.c
@@ -5,6 +5,10 @@
 // RUN: %clang_cc1 -fsanitize=unsigned-integer-overflow -fsanitize-blacklist=%t-func.blacklist -emit-llvm %s -o - | FileCheck %s --check-prefix=FUNC
 // RUN: %clang_cc1 -fsanitize=unsigned-integer-overflow -fsanitize-blacklist=%t-file.blacklist -emit-llvm %s -o - | FileCheck %s --check-prefix=FILE
 
+// RUN: rm -f %t-vfsoverlay.yaml
+// RUN: sed -e "s|DIR|%T|g" %S/Inputs/sanitizer-blacklist-vfsoverlay.yaml | sed -e "s|REAL_FILE|%t-func.blacklist|g" > %t-vfsoverlay.yaml
+// RUN: %clang_cc1 -fsanitize=unsigned-integer-overflow -fsanitize-blacklist=/Users/jankorous/src/llvm-monorepo-master/omegabuild/tools/clang/test/CodeGen/Output/only-virtual-file.blacklist -ivfsoverlay %t-vfsoverlay.yaml -emit-llvm %s -o - | FileCheck %s --check-prefix=FUNC
+
 unsigned i;
 
 // DEFAULT: @hash