[Clang][Driver] Fix include paths for `--sysroot /` on Linux

[egorzhdan]

Summary

Currently if --sysroot / is passed to the Clang driver, the include paths generated by the Clang driver will start with a double slash: //usr/include/....
If VFS is used to inject files into the include paths (for example, the Swift compiler does this), VFS will get confused and the injected files won't be visible.

This change makes sure that the include paths start with a single slash.

Fixes #28283.

[MaskRay]

clang/include/clang/Driver/ToolChain.h

219

This can use llvm::sys::path::append

[egorzhdan]

clang/include/clang/Driver/ToolChain.h

219

The implementation of this already uses llvm::sys::path::append, do you mean replacing the usages of concat with llvm::sys::path::append?
That would produce quite a lot of boilerplate I think, since llvm::sys::path::append modifies the path in-place, so every call to concat would expand into 3 lines of code. Also it would be very easy to forget to pass Style::posix and cause incorrect behavior on Windows (something I've stumbled upon while making this patch).

[MaskRay]

clang/include/clang/Driver/ToolChain.h

219

Ah I missed that. The current concat impl looks good to me.

clang/lib/Driver/ToolChains/Linux.cpp

277–278

Can the trailing / in a path component be removed now? Ditto below.

clang/test/Driver/linux-header-search.cpp

99

add -SAME whenever applicable.

[egorzhdan]

• Remove unnecessary trailing /
• Add -SAME in tests

[MaskRay]

clang/lib/Driver/ToolChain.cpp

945

I think the first argument of concat should be StringRef, then we can avoid changing the signature of getMultiarchTriple

clang/test/Driver/linux-header-search.cpp

76

I suspect this test does not add more coverage than linux-cross.cpp.

To test --sysroot with a trailing /, just modify the previous CHECK-BASIC-LIBCXXV2 by appending a /

88

Remove the otherwise empty //

It adds no value but makes { } in vim-style editors inconvenient.

[egorzhdan]

• Change arg type from std::string to StringRef
• Remove unnecessary //

• Remove unneeded test

[egorzhdan]

clang/lib/Driver/ToolChain.cpp

945

You're right, thanks!

clang/test/Driver/linux-header-search.cpp

76

CHECK-BASIC-LIBCXXV2 is not quite the same: I'd like to test the libstdc++ detection logic (e.g. GCCInstallationDetector) which doesn't get invoked for libc++.

I removed the unnecessary test.

[egorzhdan]

Rebase & fix formatting

clang/include/clang/Driver/ToolChain.h

static void addExternCSystemInclude(const llvm::opt::ArgList &DriverArgs,
                                       const Twine &Path);
   static void
       addExternCSystemIncludeIfExists(const llvm::opt::ArgList &DriverArgs,
                                       llvm::opt::ArgStringList &CC1Args,
                                       const Twine &Path);
   static void addSystemIncludes(const llvm::opt::ArgList &DriverArgs,
                                 llvm::opt::ArgStringList &CC1Args,
                                 ArrayRef<StringRef> Paths);
+
+  static std::string concat(StringRef Path, const Twine &A, const Twine &B = "",
+                            const Twine &C = "", const Twine &D = "");
   ///@}
 
 public:
   virtual ~ToolChain();
 
   // Accessors
 
   const Driver &getDriver() const { return D; }

clang/lib/Driver/ToolChain.cpp

/*static*/ void ToolChain::addSystemIncludes(const ArgList &DriverArgs,
                                              ArgStringList &CC1Args,
                                              ArrayRef<StringRef> Paths) {
   for (const auto &Path : Paths) {
     CC1Args.push_back("-internal-isystem");
     CC1Args.push_back(DriverArgs.MakeArgString(Path));
   }
 }
 
+/*static*/ std::string ToolChain::concat(StringRef Path, const Twine &A,
+                                         const Twine &B, const Twine &C,
+                                         const Twine &D) {
+  SmallString<128> Result(Path);
+  llvm::sys::path::append(Result, llvm::sys::path::Style::posix, A, B, C, D);
+  return std::string(Result);
+}
+
 std::string ToolChain::detectLibcxxVersion(StringRef IncludePath) const {
   std::error_code EC;
   int MaxVersion = 0;
   std::string MaxVersionString;
   SmallString<128> Path(IncludePath);
   llvm::sys::path::append(Path, "c++");
   for (llvm::vfs::directory_iterator LI = getVFS().dir_begin(Path, EC), LE;
        !EC && LI != LE; LI = LI.increment(EC)) {

clang/lib/Driver/ToolChains/Gnu.cpp

void Generic_GCC::GCCInstallationDetector::init(
   // installation available. GCC installs are ranked by version number.
   const GCCVersion VersionZero = GCCVersion::Parse("0.0.0");
   Version = VersionZero;
   for (const std::string &Prefix : Prefixes) {
     auto &VFS = D.getVFS();
     if (!VFS.exists(Prefix))
       continue;
     for (StringRef Suffix : CandidateLibDirs) {
-      const std::string LibDir = Prefix + Suffix.str();
+      const std::string LibDir = concat(Prefix, Suffix);
       if (!VFS.exists(LibDir))
         continue;
       // Maybe filter out <libdir>/gcc and <libdir>/gcc-cross.
       bool GCCDirExists = VFS.exists(LibDir + "/gcc");
       bool GCCCrossDirExists = VFS.exists(LibDir + "/gcc-cross");
       // Try to match the exact target triple first.
       ScanLibDirForGCCTriple(TargetTriple, Args, LibDir, TargetTriple.str(),
                              false, GCCDirExists, GCCCrossDirExists);
void Generic_GCC::GCCInstallationDetector::AddDefaultGCCPrefixes(
     StringRef SysRoot) {
   if (TargetTriple.getOS() == llvm::Triple::Solaris) {
     // Solaris is a special case.
     // The GCC installation is under
     //   /usr/gcc/<major>.<minor>/lib/gcc/<triple>/<major>.<minor>.<patch>/
     // so we need to find those /usr/gcc/*/lib/gcc libdirs and go with
     // /usr/gcc/<version> as a prefix.
 
-    std::string PrefixDir = SysRoot.str() + "/usr/gcc";
+    std::string PrefixDir = concat(SysRoot, "/usr/gcc");
     std::error_code EC;
     for (llvm::vfs::directory_iterator LI = D.getVFS().dir_begin(PrefixDir, EC),
                                        LE;
          !EC && LI != LE; LI = LI.increment(EC)) {
       StringRef VersionText = llvm::sys::path::filename(LI->path());
       GCCVersion CandidateVersion = GCCVersion::Parse(VersionText);
 
       // Filter out obviously bad entries.
if (SysRoot.empty() && TargetTriple.getOS() == llvm::Triple::Linux &&
     Prefixes.push_back("/opt/rh/devtoolset-7/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-6/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-4/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-3/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-2/root/usr");
   }
 
   // Fall back to /usr which is used by most non-Solaris systems.
-  Prefixes.push_back(SysRoot.str() + "/usr");
+  Prefixes.push_back(concat(SysRoot, "/usr"));
 }
 
 /*static*/ void Generic_GCC::GCCInstallationDetector::CollectLibDirsAndTriples(
     const llvm::Triple &TargetTriple, const llvm::Triple &BiarchTriple,
     SmallVectorImpl<StringRef> &LibDirs,
     SmallVectorImpl<StringRef> &TripleAliases,
     SmallVectorImpl<StringRef> &BiarchLibDirs,
     SmallVectorImpl<StringRef> &BiarchTripleAliases) {
for (auto &Suffix : Suffixes) {
     }
   }
 }
 
 bool Generic_GCC::GCCInstallationDetector::ScanGentooConfigs(
     const llvm::Triple &TargetTriple, const ArgList &Args,
     const SmallVectorImpl<StringRef> &CandidateTriples,
     const SmallVectorImpl<StringRef> &CandidateBiarchTriples) {
-  if (!D.getVFS().exists(D.SysRoot + GentooConfigDir))
+  if (!D.getVFS().exists(concat(D.SysRoot, GentooConfigDir)))
     return false;
 
   for (StringRef CandidateTriple : CandidateTriples) {
     if (ScanGentooGccConfig(TargetTriple, Args, CandidateTriple))
       return true;
   }
 
   for (StringRef CandidateTriple : CandidateBiarchTriples) {
     if (ScanGentooGccConfig(TargetTriple, Args, CandidateTriple, true))
       return true;
   }
   return false;
 }
 
 bool Generic_GCC::GCCInstallationDetector::ScanGentooGccConfig(
     const llvm::Triple &TargetTriple, const ArgList &Args,
     StringRef CandidateTriple, bool NeedsBiarchSuffix) {
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> File =
-      D.getVFS().getBufferForFile(D.SysRoot + GentooConfigDir + "/config-" +
-                                  CandidateTriple.str());
+      D.getVFS().getBufferForFile(concat(D.SysRoot, GentooConfigDir,
+                                         "/config-" + CandidateTriple.str()));
   if (File) {
     SmallVector<StringRef, 2> Lines;
     File.get()->getBuffer().split(Lines, "\n");
     for (StringRef Line : Lines) {
       Line = Line.trim();
       // CURRENT=triple-version
       if (!Line.consume_front("CURRENT="))
         continue;
       // Process the config file pointed to by CURRENT.
       llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> ConfigFile =
-          D.getVFS().getBufferForFile(D.SysRoot + GentooConfigDir + "/" +
-                                      Line.str());
+          D.getVFS().getBufferForFile(
+              concat(D.SysRoot, GentooConfigDir, "/" + Line));
       std::pair<StringRef, StringRef> ActiveVersion = Line.rsplit('-');
       // List of paths to scan for libraries.
       SmallVector<StringRef, 4> GentooScanPaths;
       // Scan the Config file to find installed GCC libraries path.
       // Typical content of the GCC config file:
       // LDPATH="/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x:/usr/lib/gcc/
       // (continued from previous line) x86_64-pc-linux-gnu/4.9.x/32"
       // MANPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/4.9.x/man"
for (StringRef Line : Lines) {
       }
       // Test the path based on the version in /etc/env.d/gcc/config-{tuple}.
       std::string basePath = "/usr/lib/gcc/" + ActiveVersion.first.str() + "/"
           + ActiveVersion.second.str();
       GentooScanPaths.push_back(StringRef(basePath));
 
       // Scan all paths for GCC libraries.
       for (const auto &GentooScanPath : GentooScanPaths) {
-        std::string GentooPath = D.SysRoot + std::string(GentooScanPath);
+        std::string GentooPath = concat(D.SysRoot, GentooScanPath);
         if (D.getVFS().exists(GentooPath + "/crtbegin.o")) {
           if (!ScanGCCForMultilibs(TargetTriple, Args, GentooPath,
                                    NeedsBiarchSuffix))
             continue;
 
           Version = GCCVersion::Parse(ActiveVersion.second);
           GCCInstallPath = GentooPath;
           GCCParentLibPath = GentooPath + std::string("/../../..");
Generic_GCC::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
   // Android never uses the libc++ headers installed alongside the toolchain,
   // which are generally incompatible with the NDK libraries anyway.
   if (!getTriple().isAndroid())
     if (AddIncludePath(getDriver().Dir + "/../include"))
       return;
   // If this is a development, non-installed, clang, libcxx will
   // not be found at ../include/c++ but it likely to be found at
   // one of the following two locations:
-  if (AddIncludePath(SysRoot + "/usr/local/include"))
+  if (AddIncludePath(concat(SysRoot, "/usr/local/include")))
     return;
-  if (AddIncludePath(SysRoot + "/usr/include"))
+  if (AddIncludePath(concat(SysRoot, "/usr/include")))
     return;
 }
 
 bool Generic_GCC::addLibStdCXXIncludePaths(Twine IncludeDir, StringRef Triple,
                                            Twine IncludeSuffix,
                                            const llvm::opt::ArgList &DriverArgs,
                                            llvm::opt::ArgStringList &CC1Args,
                                            bool DetectDebian) const {

clang/lib/Driver/ToolChains/Linux.cpp

case llvm::Triple::mips:
     return IsMipsR6 ? "mipsisa32r6-linux-gnu" : "mips-linux-gnu";
   case llvm::Triple::mipsel:
     if (IsAndroid)
       return "mipsel-linux-android";
     return IsMipsR6 ? "mipsisa32r6el-linux-gnu" : "mipsel-linux-gnu";
   case llvm::Triple::mips64: {
     std::string MT = std::string(IsMipsR6 ? "mipsisa64r6" : "mips64") +
                      "-linux-" + (IsMipsN32Abi ? "gnuabin32" : "gnuabi64");
-    if (D.getVFS().exists(SysRoot + "/lib/" + MT))
+    if (D.getVFS().exists(concat(SysRoot, "/lib", MT)))
       return MT;
-    if (D.getVFS().exists(SysRoot + "/lib/mips64-linux-gnu"))
+    if (D.getVFS().exists(concat(SysRoot, "/lib/mips64-linux-gnu")))
       return "mips64-linux-gnu";
     break;
   }
   case llvm::Triple::mips64el: {
     if (IsAndroid)
       return "mips64el-linux-android";
     std::string MT = std::string(IsMipsR6 ? "mipsisa64r6el" : "mips64el") +
                      "-linux-" + (IsMipsN32Abi ? "gnuabin32" : "gnuabi64");
-    if (D.getVFS().exists(SysRoot + "/lib/" + MT))
+    if (D.getVFS().exists(concat(SysRoot, "/lib", MT)))
       return MT;
-    if (D.getVFS().exists(SysRoot + "/lib/mips64el-linux-gnu"))
+    if (D.getVFS().exists(concat(SysRoot, "/lib/mips64el-linux-gnu")))
       return "mips64el-linux-gnu";
     break;
   }
   case llvm::Triple::ppc:
-    if (D.getVFS().exists(SysRoot + "/lib/powerpc-linux-gnuspe"))
+    if (D.getVFS().exists(concat(SysRoot, "/lib/powerpc-linux-gnuspe")))
       return "powerpc-linux-gnuspe";
     return "powerpc-linux-gnu";
   case llvm::Triple::ppcle:
     return "powerpcle-linux-gnu";
   case llvm::Triple::ppc64:
     return "powerpc64-linux-gnu";
   case llvm::Triple::ppc64le:
     return "powerpc64le-linux-gnu";
#endif
 
   const std::string OSLibDir = std::string(getOSLibDir(Triple, Args));
   const std::string MultiarchTriple = getMultiarchTriple(D, Triple, SysRoot);
 
   // mips32: Debian multilib, we use /libo32, while in other case, /lib is
   // used. We need add both libo32 and /lib.
   if (Arch == llvm::Triple::mips || Arch == llvm::Triple::mipsel) {
     Generic_GCC::AddMultilibPaths(D, SysRoot, "libo32", MultiarchTriple, Paths);
-    addPathIfExists(D, SysRoot + "/libo32", Paths);
-    addPathIfExists(D, SysRoot + "/usr/libo32", Paths);
+    addPathIfExists(D, concat(SysRoot, "/libo32"), Paths);
+    addPathIfExists(D, concat(SysRoot, "/usr/libo32"), Paths);
   }
   Generic_GCC::AddMultilibPaths(D, SysRoot, OSLibDir, MultiarchTriple, Paths);
 
-  addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
-  addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
+  addPathIfExists(D, concat(SysRoot, "/lib", MultiarchTriple), Paths);
+  addPathIfExists(D, concat(SysRoot, "/lib/..", OSLibDir), Paths);
 
   if (IsAndroid) {
     // Android sysroots contain a library directory for each supported OS
     // version as well as some unversioned libraries in the usual multiarch
     // directory.
     addPathIfExists(
         D,
-        SysRoot + "/usr/lib/" + MultiarchTriple + "/" +
-            llvm::to_string(Triple.getEnvironmentVersion().getMajor()),
+        concat(SysRoot, "/usr/lib", MultiarchTriple,
+               llvm::to_string(Triple.getEnvironmentVersion().getMajor())),
         Paths);
   }
 
-  addPathIfExists(D, SysRoot + "/usr/lib/" + MultiarchTriple, Paths);
+  addPathIfExists(D, concat(SysRoot, "/usr/lib", MultiarchTriple), Paths);
   // 64-bit OpenEmbedded sysroots may not have a /usr/lib dir. So they cannot
   // find /usr/lib64 as it is referenced as /usr/lib/../lib64. So we handle
   // this here.
   if (Triple.getVendor() == llvm::Triple::OpenEmbedded &&
       Triple.isArch64Bit())
-    addPathIfExists(D, SysRoot + "/usr/" + OSLibDir, Paths);
+    addPathIfExists(D, concat(SysRoot, "/usr", OSLibDir), Paths);
   else
-    addPathIfExists(D, SysRoot + "/usr/lib/../" + OSLibDir, Paths);
+    addPathIfExists(D, concat(SysRoot, "/usr/lib/..", OSLibDir), Paths);
   if (IsRISCV) {
     StringRef ABIName = tools::riscv::getRISCVABI(Args, Triple);
-    addPathIfExists(D, SysRoot + "/" + OSLibDir + "/" + ABIName, Paths);
-    addPathIfExists(D, SysRoot + "/usr/" + OSLibDir + "/" + ABIName, Paths);
+    addPathIfExists(D, concat(SysRoot, "/", OSLibDir, ABIName), Paths);
+    addPathIfExists(D, concat(SysRoot, "/usr", OSLibDir, ABIName), Paths);
   }
 
   Generic_GCC::AddMultiarchPaths(D, SysRoot, OSLibDir, Paths);
 
   // The deprecated -DLLVM_ENABLE_PROJECTS=libcxx configuration installs
   // libc++.so in D.Dir+"/../lib/". Detect this path.
   // TODO Remove once LLVM_ENABLE_PROJECTS=libcxx is unsupported.
   if (StringRef(D.Dir).startswith(SysRoot) &&
       D.getVFS().exists(D.Dir + "/../lib/libc++.so"))
     addPathIfExists(D, D.Dir + "/../lib", Paths);
 
-  addPathIfExists(D, SysRoot + "/lib", Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
+  addPathIfExists(D, concat(SysRoot, "/lib"), Paths);
+  addPathIfExists(D, concat(SysRoot, "/usr/lib"), Paths);
 }
 
 ToolChain::RuntimeLibType Linux::GetDefaultRuntimeLibType() const {
   if (getTriple().isAndroid())
     return ToolChain::RLT_CompilerRT;
   return Generic_ELF::GetDefaultRuntimeLibType();
 }
 
void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc) &&
       (!getTriple().isMusl() || DriverArgs.hasArg(options::OPT_nostdlibinc)))
     addSystemInclude(DriverArgs, CC1Args, ResourceDirInclude);
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // LOCAL_INCLUDE_DIR
-  addSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/local/include");
+  addSystemInclude(DriverArgs, CC1Args, concat(SysRoot, "/usr/local/include"));
   // TOOL_INCLUDE_DIR
   AddMultilibIncludeArgs(DriverArgs, CC1Args);
 
   // Check for configure-time C include directories.
   StringRef CIncludeDirs(C_INCLUDE_DIRS);
   if (CIncludeDirs != "") {
     SmallVector<StringRef, 5> dirs;
     CIncludeDirs.split(dirs, ":");
     for (StringRef dir : dirs) {
       StringRef Prefix =
           llvm::sys::path::is_absolute(dir) ? "" : StringRef(SysRoot);
       addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
     }
     return;
   }
 
   // On systems using multiarch and Android, add /usr/include/$triple before
   // /usr/include.
   std::string MultiarchIncludeDir = getMultiarchTriple(D, getTriple(), SysRoot);
   if (!MultiarchIncludeDir.empty() &&
-      D.getVFS().exists(SysRoot + "/usr/include/" + MultiarchIncludeDir))
-    addExternCSystemInclude(DriverArgs, CC1Args,
-                            SysRoot + "/usr/include/" + MultiarchIncludeDir);
+      D.getVFS().exists(concat(SysRoot, "/usr/include", MultiarchIncludeDir)))
+    addExternCSystemInclude(
+        DriverArgs, CC1Args,
+        concat(SysRoot, "/usr/include", MultiarchIncludeDir));
 
   if (getTriple().getOS() == llvm::Triple::RTEMS)
     return;
 
   // Add an include of '/include' directly. This isn't provided by default by
   // system GCCs, but is often used with cross-compiling GCCs, and harmless to
   // add even when Clang is acting as-if it were a system compiler.
-  addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/include");
+  addExternCSystemInclude(DriverArgs, CC1Args, concat(SysRoot, "/include"));
 
-  addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/include");
+  addExternCSystemInclude(DriverArgs, CC1Args, concat(SysRoot, "/usr/include"));
 
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc) && getTriple().isMusl())
     addSystemInclude(DriverArgs, CC1Args, ResourceDirInclude);
 }
 
 void Linux::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                      llvm::opt::ArgStringList &CC1Args) const {
   // We need a detected GCC installation on Linux to provide libstdc++'s

clang/test/Driver/linux-header-search.cpp

 // RUN:     --sysroot=%S/Inputs/basic_linux_libcxx_tree \
 // RUN:     --gcc-toolchain="" \
 // RUN:   | FileCheck --check-prefix=CHECK-BASIC-LIBCXX-SYSROOT %s
 // CHECK-BASIC-LIBCXX-SYSROOT: "-cc1"
 // CHECK-BASIC-LIBCXX-SYSROOT: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK-BASIC-LIBCXX-SYSROOT: "-internal-isystem" "[[SYSROOT]]/usr/include/x86_64-unknown-linux-gnu/c++/v1"
 // CHECK-BASIC-LIBCXX-SYSROOT: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"
 // CHECK-BASIC-LIBCXX-SYSROOT: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
+
+// Test include paths when the sysroot path ends with `/`.
+// RUN: %clang -### %s -fsyntax-only 2>&1 \
+// RUN:     --target=x86_64-unknown-linux-gnu \
+// RUN:     -stdlib=libc++ \
+// RUN:     -ccc-install-dir %S/Inputs/basic_linux_tree/usr/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir \
+// RUN:     --sysroot=%S/Inputs/basic_linux_libcxx_tree/ \
+// RUN:     --gcc-toolchain="" \
+// RUN:   | FileCheck --check-prefix=CHECK-BASIC-LIBCXX-SYSROOT-SLASH %s
+// CHECK-BASIC-LIBCXX-SYSROOT-SLASH: "-cc1"
+// CHECK-BASIC-LIBCXX-SYSROOT-SLASH-SAME: "-isysroot" "[[SYSROOT:[^"]+/]]"
+// CHECK-BASIC-LIBCXX-SYSROOT-SLASH-SAME: "-internal-isystem" "[[SYSROOT]]usr/include/x86_64-unknown-linux-gnu/c++/v1"
+// CHECK-BASIC-LIBCXX-SYSROOT-SLASH-SAME: "-internal-isystem" "[[SYSROOT]]usr/include/c++/v1"
+// CHECK-BASIC-LIBCXX-SYSROOT-SLASH-SAME: "-internal-isystem" "[[SYSROOT]]usr/local/include"
+
 // RUN: %clang -### %s -fsyntax-only 2>&1 \
 // RUN:     --target=x86_64-unknown-linux-gnu \
 // RUN:     -stdlib=libc++ \
 // RUN:     -ccc-install-dir %S/Inputs/basic_linux_libcxx_tree/usr/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir \
 // RUN:     --sysroot=%S/Inputs/basic_linux_libcxx_tree \
 // RUN:     --gcc-toolchain="" \
 // RUN:   | FileCheck --check-prefix=CHECK-BASIC-LIBCXX-INSTALL %s

 // RUN:     --sysroot=%S/Inputs/basic_linux_libcxxv2_tree \
 // RUN:     --gcc-toolchain="" \
 // RUN:   | FileCheck --check-prefix=CHECK-BASIC-LIBCXXV2-INSTALL %s
 // CHECK-BASIC-LIBCXXV2-INSTALL: "-cc1"
 // CHECK-BASIC-LIBCXXV2-INSTALL: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK-BASIC-LIBCXXV2-INSTALL: "-internal-isystem" "[[SYSROOT]]/usr/bin/../include/x86_64-unknown-linux-gnu/c++/v2"
 // CHECK-BASIC-LIBCXXV2-INSTALL: "-internal-isystem" "[[SYSROOT]]/usr/bin/../include/c++/v2"
 // CHECK-BASIC-LIBCXXV2-INSTALL: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
-//
+
+// Test Linux with libstdc++ when the sysroot path ends with `/`.
+// RUN: %clang -### %s -fsyntax-only 2>&1 \
+// RUN:     --target=x86_64-unknown-linux-gnu \
+// RUN:     -stdlib=libstdc++ \
+// RUN:     -ccc-install-dir %S/Inputs/basic_linux_tree/usr/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir \
+// RUN:     --sysroot=%S/Inputs/basic_linux_libstdcxx_tree/ \
+// RUN:     --gcc-toolchain="" \
+// RUN:   | FileCheck --check-prefix=CHECK-BASIC-LIBSTDCXX-SYSROOT-SLASH %s
+// CHECK-BASIC-LIBSTDCXX-SYSROOT-SLASH: "-cc1"
+// CHECK-BASIC-LIBSTDCXX-SYSROOT-SLASH-SAME: "-isysroot" "[[SYSROOT:[^"]+/]]"
+// CHECK-BASIC-LIBSTDCXX-SYSROOT-SLASH-SAME: "-internal-isystem" "[[SYSROOT]]usr/lib/gcc/x86_64-unknown-linux-gnu/4.8/../../../../x86_64-unknown-linux-gnu/include"
+
 // Test Linux with both libc++ and libstdc++ installed.
 // RUN: %clang -### %s -fsyntax-only 2>&1 \
 // RUN:     --target=x86_64-unknown-linux-gnu \
 // RUN:     -stdlib=libc++ \
 // RUN:     -ccc-install-dir %S/Inputs/basic_linux_tree/usr/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir \
 // RUN:     --sysroot=%S/Inputs/basic_linux_libstdcxx_libcxxv2_tree \
 // RUN:     --gcc-toolchain="" \
 // RUN:   | FileCheck --check-prefix=CHECK-BASIC-LIBSTDCXX-LIBCXXV2-SYSROOT %s
 // CHECK-BASIC-LIBSTDCXX-LIBCXXV2-SYSROOT: "-cc1"
 // CHECK-BASIC-LIBSTDCXX-LIBCXXV2-SYSROOT: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK-BASIC-LIBSTDCXX-LIBCXXV2-SYSROOT: "-internal-isystem" "[[SYSROOT]]/usr/include/x86_64-unknown-linux-gnu/c++/v2"
 // CHECK-BASIC-LIBSTDCXX-LIBCXXV2-SYSROOT: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v2"
 // CHECK-BASIC-LIBSTDCXX-LIBCXXV2-SYSROOT: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
 
 // Test Gentoo's weirdness both before and after they changed it in their GCC
 // 4.6.4 release.
 // RUN: %clang -### %s -fsyntax-only 2>&1 \
 // RUN:     --target=x86_64-unknown-linux-gnu -stdlib=libstdc++ \