Index: lldb/include/lldb/Core/Module.h
===================================================================
--- lldb/include/lldb/Core/Module.h
+++ lldb/include/lldb/Core/Module.h
@@ -20,6 +20,7 @@
 #include "lldb/Utility/ConstString.h"
 #include "lldb/Utility/FileSpec.h"
 #include "lldb/Utility/Status.h"
+#include "lldb/Utility/SDK.h"
 #include "lldb/Utility/UUID.h"
 #include "lldb/lldb-defines.h"
 #include "lldb/lldb-enumerations.h"
@@ -509,6 +510,12 @@
     m_mod_time = mod_time;
   }
 
+  /// This callback will be called by SymbolFile implementations when
+  /// parsing a compile unit that contains SDK information.
+  /// \param sdk will be merged with \p m_sdk.
+  /// \param sysroot will be added to the path remapping dictionary.
+  void RegisterSDK(SDK sdk, ConstString sysroot);
+
   /// Tells whether this module is capable of being the main executable for a
   /// process.
   ///
@@ -971,6 +978,10 @@
   /// module that doesn't match where the sources currently are.
   PathMappingList m_source_mappings =
       ModuleList::GetGlobalModuleListProperties().GetSymlinkMappings();
+
+  /// The SDK this module was compiled with.
+  SDK m_sdk;
+  
   lldb::SectionListUP m_sections_up; ///< Unified section list for module that
                                      /// is used by the ObjectFile and and
                                      /// ObjectFile instances for the debug info
Index: lldb/include/lldb/Target/Platform.h
===================================================================
--- lldb/include/lldb/Target/Platform.h
+++ lldb/include/lldb/Target/Platform.h
@@ -434,6 +434,8 @@
     return lldb_private::ConstString();
   }
 
+  virtual ConstString GetSDKPath(int type) { return {}; }
+
   const std::string &GetRemoteURL() const { return m_remote_url; }
 
   bool IsHost() const {
Index: lldb/include/lldb/Utility/SDK.h
===================================================================
--- /dev/null
+++ lldb/include/lldb/Utility/SDK.h
@@ -0,0 +1,43 @@
+//===-- SDK.h ---------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_UTILITY_SDK_H
+#define LLDB_UTILITY_SDK_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/VersionTuple.h"
+#include <tuple>
+
+namespace lldb_private {
+
+/// An abstraction for Apple SDKs that works like \p llvm::Triple.
+class SDK {
+  ConstString m_name;
+
+public:
+  SDK() = default;
+  SDK(const char *name) : m_name(name, true) {}
+  SDK(ConstString name) : m_name(name) {}
+
+  /// The merge function follows a strict order:
+  /// 1. SDK with the higher SDKType wins.
+  /// 2. The newer SDK wins.
+  void Merge(SDK other);
+
+  SDK &operator=(SDK other);
+  bool operator==(SDK other);
+
+  /// Return parsed SDK number, and SDK version number.
+  std::tuple<int, llvm::VersionTuple> Parse() const;
+  llvm::VersionTuple GetVersion() const;
+  int GetSDKType() const;
+};
+
+} // namespace lldb_private
+
+#endif
Index: lldb/source/Core/Module.cpp
===================================================================
--- lldb/source/Core/Module.cpp
+++ lldb/source/Core/Module.cpp
@@ -1596,6 +1596,21 @@
   return m_source_mappings.RemapPath(path, new_path);
 }
 
+void Module::RegisterSDK(SDK sdk, ConstString sysroot) {
+  if (m_sdk == sdk)
+    return;
+  m_sdk.Merge(sdk);
+  PlatformSP host_platform = Platform::GetHostPlatform();
+  ConstString host_sdk_path = host_platform->GetSDKPath(sdk.GetSDKType());
+  if (!host_sdk_path)
+    return;
+  // If merged SDK changed for a previously registered source path, update it.
+  // This could happend with -fdebug-prefix-map, otherwise it's unlikely.
+  if (!m_source_mappings.Replace(sysroot, host_sdk_path, true))
+    // In the general case, however, append it to the list.
+    m_source_mappings.Append(sysroot, host_sdk_path, false);
+}
+
 bool Module::MergeArchitecture(const ArchSpec &arch_spec) {
   if (!arch_spec.IsValid())
     return false;
Index: lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.h
===================================================================
--- lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.h
+++ lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.h
@@ -11,6 +11,7 @@
 
 #include "Plugins/Platform/POSIX/PlatformPOSIX.h"
 #include "lldb/Host/FileSystem.h"
+#include "lldb/Utility/ConstString.h"
 #include "lldb/Utility/FileSpec.h"
 #include "lldb/Utility/StructuredData.h"
 #include "llvm/ADT/StringRef.h"
@@ -96,6 +97,8 @@
   llvm::Expected<lldb_private::StructuredData::DictionarySP>
   FetchExtendedCrashInformation(lldb_private::Process &process) override;
 
+  lldb_private::ConstString GetSDKPath(int type) override;
+  
   static llvm::StringRef GetSDKNameForType(SDKType type);
   static lldb_private::FileSpec GetXcodeSDK(SDKType type);
   static lldb_private::FileSpec GetXcodeContentsDirectory();
@@ -184,6 +187,7 @@
   static std::string FindXcodeContentsDirectoryInPath(llvm::StringRef path);
 
   std::string m_developer_directory;
+  std::array<lldb_private::ConstString, numSDKTypes> m_sdk_path;
 
 private:
   DISALLOW_COPY_AND_ASSIGN(PlatformDarwin);
Index: lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.cpp
===================================================================
--- lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.cpp
+++ lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.cpp
@@ -1282,6 +1282,81 @@
   return g_command_line_tools_filespec;
 }
 
+SDK &SDK::operator=(SDK other) {
+  m_name = other.m_name;
+  return *this;
+}
+
+bool SDK::operator==(SDK other) {
+  return m_name == other.m_name;
+}
+
+static PlatformDarwin::SDKType ParseSDKName(llvm::StringRef &name) {
+  if (name.consume_front("MacOSX"))
+    return PlatformDarwin::MacOSX;
+  if (name.consume_front("iPhoneSimulator"))
+    return PlatformDarwin::iPhoneSimulator;
+  if (name.consume_front("iPhoneOS"))
+    return PlatformDarwin::iPhoneOS;
+  if (name.consume_front("AppleTVSimulator"))
+    return PlatformDarwin::AppleTVSimulator;
+  if (name.consume_front("AppleTVOS"))
+    return PlatformDarwin::AppleTVOS;
+  if (name.consume_front("WatchSimulator"))
+    return PlatformDarwin::WatchSimulator;
+  if (name.consume_front("WatchOS"))
+    return PlatformDarwin::watchOS;
+  if (name.consume_front("bridgeOS"))
+    return PlatformDarwin::bridgeOS;
+  if (name.consume_front("Linux"))
+    return PlatformDarwin::Linux;
+  static_assert(PlatformDarwin::Linux == PlatformDarwin::numSDKTypes - 1,
+                "New SDK type was added, update this list!");
+  return PlatformDarwin::unknown;
+}
+
+static llvm::VersionTuple ParseSDKVersion(llvm::StringRef &name) {
+  unsigned i = 0;
+  while (i < name.size() && name[i] >= '0' && name[i] <= '9')
+    ++i;
+  if (name[i++] != '.')
+    return {};
+  while (i < name.size() && name[i] >= '0' && name[i] <= '9')
+    ++i;
+  if (name[i++] != '.')
+    return {};
+
+  llvm::VersionTuple version;
+  version.tryParse(name.slice(0, i - 1));
+  name = name.drop_front(i);
+  return {};
+}
+
+
+std::tuple<int, llvm::VersionTuple> SDK::Parse() const {
+  llvm::StringRef input = m_name.GetStringRef();
+  PlatformDarwin::SDKType sdk = ParseSDKName(input);
+  llvm::VersionTuple version = ParseSDKVersion(input);
+  return {sdk, version};
+}
+
+llvm::VersionTuple SDK::GetVersion() const {
+  llvm::StringRef input = m_name.GetStringRef();
+  ParseSDKName(input);
+  return ParseSDKVersion(input);
+}
+
+int SDK::GetSDKType() const {
+  llvm::StringRef input = m_name.GetStringRef();
+  return ParseSDKName(input);
+}
+
+void SDK::Merge(SDK other) {
+  // The "bigger" SDK always wins.
+  if (Parse() < other.Parse())
+    *this = other;
+}
+
 bool PlatformDarwin::SDKSupportsModules(SDKType sdk_type,
                                         llvm::VersionTuple version) {
   switch (sdk_type) {
@@ -1894,6 +1969,14 @@
   llvm_unreachable("unhandled switch case");
 }
 
+ConstString PlatformDarwin::GetSDKPath(int type) {
+  if (type >= numSDKTypes || type <= unknown)
+    return {};
+  if (!m_sdk_path[type])
+    m_sdk_path[type] = GetXcodeSDK((SDKType)type).GetDirectory();
+  return m_sdk_path[type];
+}
+
 FileSpec PlatformDarwin::GetXcodeSDK(SDKType type) {
   std::string xcrun_cmd =
       "xcrun --show-sdk-path --sdk " + GetSDKNameForType(type).str();
Index: lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.h
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.h
+++ lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.h
@@ -12,6 +12,7 @@
 #include "DWARFDIE.h"
 #include "DWARFDebugInfoEntry.h"
 #include "lldb/lldb-enumerations.h"
+#include "lldb/Utility/SDK.h"
 #include "llvm/Support/RWMutex.h"
 #include <atomic>
 
@@ -197,6 +198,10 @@
 
   uint32_t GetProducerVersionUpdate();
 
+  lldb_private::SDK GetSDK();
+
+  llvm::StringRef GetSysroot();
+
   uint64_t GetDWARFLanguageType();
 
   bool GetIsOptimized();
Index: lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
@@ -667,6 +667,18 @@
   return *m_language_type;
 }
 
+SDK DWARFUnit::GetSDK() {
+  if (const DWARFDebugInfoEntry *die = GetUnitDIEPtrOnly())
+    return SDK(die->GetAttributeValueAsString(this, DW_AT_APPLE_sdk, ""));
+  return {};
+}
+
+llvm::StringRef DWARFUnit::GetSysroot() {
+  if (const DWARFDebugInfoEntry *die = GetUnitDIEPtrOnly())
+    return die->GetAttributeValueAsString(this, DW_AT_LLVM_sysroot, "");
+  return {};
+}
+
 bool DWARFUnit::GetIsOptimized() {
   if (m_is_optimized == eLazyBoolCalculate) {
     const DWARFDebugInfoEntry *die = GetUnitDIEPtrOnly();
Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -648,6 +648,7 @@
         const DWARFBaseDIE cu_die =
             dwarf_cu.GetNonSkeletonUnit().GetUnitDIEOnly();
         if (cu_die) {
+          module_sp->RegisterSDK(dwarf_cu.GetSDK(), ConstString(dwarf_cu.GetSysroot()));
           FileSpec cu_file_spec(cu_die.GetName(), dwarf_cu.GetPathStyle());
           if (cu_file_spec) {
             // If we have a full path to the compile unit, we don't need to