[Driver] Update GCC libraries detection logic for Gentoo.

[manojgupta]

Summary

1. Find GCC's LDPATH from the actual GCC config file.
2. Avoid picking libraries from a similar named tuple if the exact tuple is installed.

[manojgupta]

Michał, will appreciate if you can test this on your (multiple?) Gentoo configurations.
Will work on updating the testcases after that.

To test it locally, I used the following :

$ cat test.cpp

#include <iostream>
#include <string>

int main() {
  std::cout << " Hello, World!" << std::endl;
  return 0;
}

Setup cross compilers for x86_64 and aarch64.

$ sudo crossdev -S x86_64-gentoo-linux-gnu
$ sudo crossdev -S aarch64-gentoo-linux-gnu

$ Build and install clang in a location other than /usr/bin e.g. $HOME/clang-testing/bin
Verify that correct gcc libs are picked.
$ /path/to/clang++ --sysroot=/usr/aarch64-gentoo-linux-gnu -B/usr/libexec/gcc/aarch64-gentoo-linux-gnu -target aarch64-gentoo-linux-gnu test.cpp -o main -Wl,-t -v

Further verify that any lib/headers from x86_64-pc-linux-gnu are NOT picked after the patch is applied.
$ /path/to/clang++ --sysroot=/usr/x86_64-gentoo-linux-gnu -B/usr/libexec/gcc/x86_64-gentoo-linux-gnu -target x86_64-gentoo-linux-gnu test.cpp -o main -Wl,-t -v

[manojgupta]

Chandler, I recall that you are also a Gentoo user so please take a look.

[mgorny]

lib/Driver/ToolChains/Gnu.cpp

2287

I'm not sure if there's a point in keeping this if you actually parse the config file. I can't think of a really valid case when GCC would be installed without LDPATH in the config file. Not saying it's wrong. You may want at least to push it after the configfile paths though.

2290

Typo: 'libaries'

2299

Misindent.

2303

This probably doesn't harm but I'd prefer if quotes weren't considered an obligatory part of the string. I'd rather grab it by LDPATH= and strip quotes afterwards if present on both sides. But I won't insist on this.

2306

Here you seem to assume that there would be at most 2 paths. That's a wrong assumption — there are triple-ABI targets (e.g. amd64 with x32 variant), and there is no reason prohibiting more LDPATHs. So please use the 'full' split, and iterate over all paths.

[manojgupta]

Address requested changes.

[manojgupta]

lib/Driver/ToolChains/Gnu.cpp

2306

I had forgotten about x32. Splitting to get all paths is the right thing to do anyway.

[mgorny]

Thanks. Besides that one tiny nit, looks good at a first glance. I'll test it tomorrow or the next day (but only for the most basic use, sorry).

However, I do not feel confident enough with Clang code to ack change this large on my own. So let's wait for @chandlerc to take a second look, or maybe try to add more reviewers.

lib/Driver/ToolChains/Gnu.cpp

2303

Well, I meant stripping them if both are present. However, this is not a biggie.

[manojgupta]

Adding more reviewers.

[rnk]

Thousands of lines of C++ to answer one of life's most simple questions: where are the libraries and where are the headers. =p

lgtm

lib/Driver/ToolChains/Gnu.cpp

2229–2278

Can you break the loop here to reduce indentation of the config parsing logic below?

[manojgupta]

Fix some typos.
Reduced indent in the loop.

[manojgupta]

Fix a bug in passing the actual path when libraries are present in sysroot.

[manojgupta]

Modified an existing gentoo sysroot as the test case. Please let me know if you want me checkin a new sysroot.

[manojgupta]

Avoid double appending of sysroot prefix to base path.

[mgorny]

If that's not a problem, then the more tests, the merrier ;-). Preferably something specific to crossdev would be helpful, given this is a new use case, and/or something that would actually have directory mismatches with CURRENT entry name (i.e. that wouldn't have worked before).

[manojgupta]

Updated tests and added a sysroot to test that LDLIBS are picked by
parsing /etc/env.d/gcc/tuple-version file.

[mgorny]

Ok, I've tried it on top of clang-6.0.0 and I get the following test failures:

Failing Tests (8):
    Clang :: Driver/android-ndk-standalone.cpp
    Clang :: Driver/constructors.c
    Clang :: Driver/cuda-detect.cu
    Clang :: Driver/env.c
    Clang :: Driver/gcc-version-debug.c
    Clang :: Driver/linux-header-search.cpp
    Clang :: Driver/linux-ld.c
    Clang :: Driver/pic.c

Could you check whether the tests pass for you? Me using 6.0.0 may be the culprit here but I don't think it should have such significant effect.

[manojgupta]

My understanding is that some of the tests are failing since we are scanning for Gentoo specific GCC installation first in both sysroot and "/". So, clang succeeds in find the libraries in "/usr/lib/gcc" even when sysroot argument is passed.
Previously, "/usr/lib/gcc" was not scanned when sysroot was passed.

Maybe, it is better to add /usr to list of paths to search instead of scanning in "/"?

Basically, Remove the newly added line 2245: SysRootPrefixes.push_back("");
and instead do Prefixes.push_back("/usr") ?

[mgorny]

Ok, that's a problem. I think we really ought to consider all possibilites of sysroot first, and either do not fall back to main system at all or do that only if sysroot doesn't have any install at all. Basically, it is important that we don't break non-Gentoo sysroots, even when running on top of Gentoo.

I don't really understand what you mean with the prefixes stuff but it doesn't sound like it's going to solve the problem.

[manojgupta]

I think the tests are already broken in Gentoo when clang is installed in /usr/bin even without this patch. The tests only work if clang binary is not installed in /usr/bin.

RootCause is the existing lines in Gnu.cpp:

// Then look for gcc installed alongside clang.
Prefixes.push_back(D.InstalledDir + "/..");

e.g. Specified debian sysroot is not picked as expected for the following command line.

$ clang -v --target=i386-unknown-linux --gcc-toolchain="" --sysroot=test/Driver/Inputs/debian_multiarch_tree 2>&1
clang version 7.0.0
Target: i386-unknown-linux
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-pc-linux-gnu/4.9.x
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-pc-linux-gnu/4.9.x
Found candidate GCC installation: /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x
Found candidate GCC installation: test/Driver/Inputs/debian_multiarch_tree/usr/lib/gcc/i686-linux-gnu/4.5
Found candidate GCC installation: test/Driver/Inputs/debian_multiarch_tree/usr/lib/gcc/x86_64-linux-gnu/4.5
Selected GCC installation: /usr/bin/../lib/gcc/i686-pc-linux-gnu/4.9.x
Candidate multilib: .;@m32
Selected multilib: .;@m32

[mgorny]

To be honest, I don't really know. But since we're not installing it straight to /usr, I suppose that's not a problem we need to solve right now.

However, they do work with clang installed in /usr/lib/llvm/*/bin, and this patch must not regress that. So if your /usr hack solves that, I don't see a problem with it.

[manojgupta]

Can solve crossdev issue by passing -gcc-toolchain=/usr
so just detect gcc libs as an offset to sysroot for now.

[manojgupta]

Michał, can you give the latest change a try? Hopefully it should not break any tests.

[mgorny]

Well, it's better:

Failing Tests (1):
    Clang :: Driver/linux-header-search.cpp

It is apparently the new test failing:

+ /var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/clang -no-canonical-prefixes /var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/linux-header-search.cpp -### -fsyntax-only -target i386-unknown-linux-gnu -stdlib=libstdc++ --sysroot=/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_multi_version_tree --gcc-toolchain=
+ /var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/clang -no-canonical-prefixes /var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/linux-header-search.cpp -### -fsyntax-only -target x86_64-unknown-linux-gnu -stdlib=libstdc++ --sysroot=/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree --gcc-toolchain=
+ /usr/lib64/llvm/6/bin/FileCheck --check-prefix=CHECK-GENTOO-4-9-X /var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/linux-header-search.cpp
/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/linux-header-search.cpp:359:24: error: expected string not found in input
// CHECK-GENTOO-4-9-X: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3"
                       ^
<stdin>:5:752: note: scanning from here
 "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/clang" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-fsyntax-only" "-disable-free" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "linux-header-search.cpp" "-mrelocation-model" "static" "-mthread-model" "posix" "-mdisable-fp-elim" "-fmath-errno" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-fuse-init-array" "-target-cpu" "x86-64" "-dwarf-column-info" "-debugger-tuning=gdb" "-resource-dir" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/../../../../lib/clang/6.0.0" "-isysroot" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree" "-internal-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/usr/local/include" "-internal-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/../../../../lib/clang/6.0.0/include" "-internal-externc-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/include" "-internal-externc-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/usr/include" "-fdeprecated-macro" "-fdebug-compilation-dir" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/test/Driver" "-ferror-limit" "19" "-fmessage-length" "0" "-fobjc-runtime=gcc" "-fcxx-exceptions" "-fexceptions" "-fdiagnostics-show-option" "-x" "c++" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/linux-header-search.cpp"
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               ^
<stdin>:5:752: note: with variable "SYSROOT" equal to "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree"
 "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/clang" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-fsyntax-only" "-disable-free" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "linux-header-search.cpp" "-mrelocation-model" "static" "-mthread-model" "posix" "-mdisable-fp-elim" "-fmath-errno" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-fuse-init-array" "-target-cpu" "x86-64" "-dwarf-column-info" "-debugger-tuning=gdb" "-resource-dir" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/../../../../lib/clang/6.0.0" "-isysroot" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree" "-internal-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/usr/local/include" "-internal-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/bin/../../../../lib/clang/6.0.0/include" "-internal-externc-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/include" "-internal-externc-isystem" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/usr/include" "-fdeprecated-macro" "-fdebug-compilation-dir" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src-abi_x86_32.x86/test/Driver" "-ferror-limit" "19" "-fmessage-length" "0" "-fobjc-runtime=gcc" "-fcxx-exceptions" "-fexceptions" "-fdiagnostics-show-option" "-x" "c++" "/var/tmp/portage/sys-devel/clang-6.0.0-r1/work/x/y/cfe-6.0.0.src/test/Driver/linux-header-search.cpp"
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               ^

--

********************

[manojgupta]

I can't reproduce this using the trunk llvm. Does it pass for you if %clang is replaced by %clang++ in the test case?

[mgorny]

I'm sorry, I see the problem now — the diff generated by Phabricator does not include the empty files x_x (seriously, this thing keeps surprising me in how broken it could be). I'm going to try again with correct file set tonight or tomorrow. If you could send the complete patch (preferably -p1 if you have one) to mgorny AT gentoo.org, that would also be helpful.

[mgorny]

Works fine, thanks a lot! Note that I haven't tested crossdev or anything special, just regular multilib.

lib/Driver/ToolChains/Gnu.h

bool ScanGCCForMultilibs(const llvm::Triple &TargetTriple,
                              bool NeedsBiarchSuffix = false);
 
     void ScanLibDirForGCCTriple(const llvm::Triple &TargetArch,
                                 const llvm::opt::ArgList &Args,
                                 const std::string &LibDir,
                                 StringRef CandidateTriple,
                                 bool NeedsBiarchSuffix = false);
 
+    bool ScanGentooConfigs(const llvm::Triple &TargetTriple,
+                           const llvm::opt::ArgList &Args,
+                           const SmallVectorImpl<StringRef> &CandidateTriples,
+                           const SmallVectorImpl<StringRef> &BiarchTriples);
+
     bool ScanGentooGccConfig(const llvm::Triple &TargetTriple,
                              const llvm::opt::ArgList &Args,
                              StringRef CandidateTriple,
                              bool NeedsBiarchSuffix = false);
   };
 
 protected:
   GCCInstallationDetector GCCInstallation;

lib/Driver/ToolChains/Gnu.cpp

if (GCCToolchainDir != "") {
     }
   }
 
   // Try to respect gcc-config on Gentoo. However, do that only
   // if --gcc-toolchain is not provided or equal to the Gentoo install
   // in /usr. This avoids accidentally enforcing the system GCC version
   // when using a custom toolchain.
   if (GCCToolchainDir == "" || GCCToolchainDir == D.SysRoot + "/usr") {
-    for (StringRef CandidateTriple : ExtraTripleAliases) {
-      if (ScanGentooGccConfig(TargetTriple, Args, CandidateTriple))
-        return;
-    }
-    for (StringRef CandidateTriple : CandidateTripleAliases) {
-      if (ScanGentooGccConfig(TargetTriple, Args, CandidateTriple))
-        return;
-    }
-    for (StringRef CandidateTriple : CandidateBiarchTripleAliases) {
-      if (ScanGentooGccConfig(TargetTriple, Args, CandidateTriple, true))
-        return;
-    }
-  }
+    SmallVector<StringRef, 16> GentooTestTriples;
+    // Try to match an exact triple as target triple first.
+    // e.g. crossdev -S x86_64-gentoo-linux-gnu will install gcc libs for
+    // x86_64-gentoo-linux-gnu. But "clang -target x86_64-gentoo-linux-gnu"
+    // may pick the libraries for x86_64-pc-linux-gnu even when exact matching
+    // triple x86_64-gentoo-linux-gnu is present.
+    GentooTestTriples.push_back(TargetTriple.str());
+    // Check rest of triples.
+    GentooTestTriples.append(ExtraTripleAliases.begin(),
+                             ExtraTripleAliases.end());
+    GentooTestTriples.append(CandidateTripleAliases.begin(),
+                             CandidateTripleAliases.end());
+    if (ScanGentooConfigs(TargetTriple, Args, GentooTestTriples,
+                          CandidateBiarchTripleAliases))
 
   // Loop over the various components which exist and select the best GCC
   // installation available. GCC installs are ranked by version number.
   Version = GCCVersion::Parse("0.0.0");
   for (const std::string &Prefix : Prefixes) {
     if (!D.getVFS().exists(Prefix))
       continue;
     for (StringRef Suffix : CandidateLibDirs) {
       const std::string LibDir = Prefix + Suffix.str();
       if (!D.getVFS().exists(LibDir))
         continue;
+      // Try to match the exact target triple first.
+      ScanLibDirForGCCTriple(TargetTriple, Args, LibDir, TargetTriple.str());
+      // Try rest of possible triples.
       for (StringRef Candidate : ExtraTripleAliases) // Try these first.
         ScanLibDirForGCCTriple(TargetTriple, Args, LibDir, Candidate);
       for (StringRef Candidate : CandidateTripleAliases)
         ScanLibDirForGCCTriple(TargetTriple, Args, LibDir, Candidate);
     }
     for (StringRef Suffix : CandidateBiarchLibDirs) {
       const std::string LibDir = Prefix + Suffix.str();
       if (!D.getVFS().exists(LibDir))
for (vfs::directory_iterator
       // Linux.
       GCCInstallPath = (LibDir + "/" + LibSuffix + "/" + VersionText).str();
       GCCParentLibPath = (GCCInstallPath + "/../" + Suffix.ReversePath).str();
       IsValid = true;
     }
   }
 }
 
+bool Generic_GCC::GCCInstallationDetector::ScanGentooConfigs(
+    const llvm::Triple &TargetTriple, const ArgList &Args,
+    const SmallVectorImpl<StringRef> &CandidateTriples,
+    const SmallVectorImpl<StringRef> &CandidateBiarchTriples) {
+  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 + "/etc/env.d/gcc/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=")) {
-        const std::pair<StringRef, StringRef> ActiveVersion =
-          Line.rsplit('-');
-        // Note: Strictly speaking, we should be reading
-        // /etc/env.d/gcc/${CURRENT} now. However, the file doesn't
-        // contain anything new or especially useful to us.
-        const std::string GentooPath = D.SysRoot + "/usr/lib/gcc/" +
-                                       ActiveVersion.first.str() + "/" +
-                                       ActiveVersion.second.str();
+      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 + "/etc/env.d/gcc/" +
+                                      Line.str());
+      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"
+      // INFOPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/4.9.x/info"
+      // STDCXX_INCDIR="/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4"
+      // We are looking for the paths listed in LDPATH=... .
+      if (ConfigFile) {
+        SmallVector<StringRef, 2> ConfigLines;
+        ConfigFile.get()->getBuffer().split(ConfigLines, "\n");
+        for (StringRef ConfLine : ConfigLines) {
+          ConfLine = ConfLine.trim();
+          if (ConfLine.consume_front("LDPATH=")) {
+            // Drop '"' from front and back if present.
+            ConfLine.consume_back("\"");
+            ConfLine.consume_front("\"");
+            // Get all paths sperated by ':'
+            ConfLine.split(GentooScanPaths, ':', -1, /*AllowEmpty*/ false);
+          }
+        }
+      }
+      // 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);
         if (D.getVFS().exists(GentooPath + "/crtbegin.o")) {
           if (!ScanGCCForMultilibs(TargetTriple, Args, GentooPath,
                                    NeedsBiarchSuffix))
-            return false;
+            continue;
 
           Version = GCCVersion::Parse(ActiveVersion.second);
           GCCInstallPath = GentooPath;
-          GCCParentLibPath = GentooPath + "/../../..";
+          GCCParentLibPath = GentooPath + std::string("/../../..");
           GCCTriple.setTriple(ActiveVersion.first);
           IsValid = true;
           return true;
         }
       }
     }
   }
 
   return false;
 }
 
 Generic_GCC::Generic_GCC(const Driver &D, const llvm::Triple &Triple,
                          const ArgList &Args)
     : ToolChain(D, Triple, Args), GCCInstallation(D),
       CudaInstallation(D, Triple, Args) {
   getProgramPaths().push_back(getDriver().getInstalledDir());
   if (getDriver().getInstalledDir() != getDriver().Dir)
     getProgramPaths().push_back(getDriver().Dir);
 }
 
 Generic_GCC::~Generic_GCC() {}
 
 Tool *Generic_GCC::getTool(Action::ActionClass AC) const {
   switch (AC) {
   case Action::PreprocessJobClass:
     if (!Preprocess)
       Preprocess.reset(new clang::driver::tools::gcc::Preprocessor(*this));
     return Preprocess.get();
   case Action::CompileJobClass:
     if (!Compile)
       Compile.reset(new tools::gcc::Compiler(*this));
     return Compile.get();
   default:
     return ToolChain::getTool(AC);
   }
 }
 
 Tool *Generic_GCC::buildAssembler() const {

test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/etc/env.d/gcc/config-x86_64-pc-linux-gnu

+CURRENT=x86_64-pc-linux-gnu-4.9.3

test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/etc/env.d/gcc/x86_64-pc-linux-gnu-4.9.3

+PATH="/usr/x86_64-pc-linux-gnu/gcc-bin/4.9.x"
+ROOTPATH="/usr/x86_64-pc-linux-gnu/gcc-bin/4.9.x"
+GCC_PATH="/usr/x86_64-pc-linux-gnu/gcc-bin/4.9.x"
+LDPATH="/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/32:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/x32"
+MANPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/4.9.x/man"
+INFOPATH="/usr/share/gcc-data/x86_64-pc-linux-gnu/4.9.x/info"
+STDCXX_INCDIR="g++-v4"
+CTARGET="x86_64-pc-linux-gnu"
+GCC_SPECS=""
+MULTIOSDIRS="../lib64:../lib32"

test/Driver/Inputs/gentoo_linux_gcc_4.9.x_tree/etc/gentoo-release

+Gentoo Base System release 2.3

test/Driver/linux-header-search.cpp

 // CHECK-GENTOO-4-9-3-32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4.9.3"
 // CHECK-GENTOO-4-9-3-32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4.9.3/x86_64-pc-linux-gnu/32"
 // CHECK-GENTOO-4-9-3-32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4.9.3/backward"
 // CHECK-GENTOO-4-9-3-32: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
 // CHECK-GENTOO-4-9-3-32: "-internal-isystem" "[[RESOURCE_DIR]]{{/|\\\\}}include"
 // CHECK-GENTOO-4-9-3-32: "-internal-externc-isystem" "[[SYSROOT]]/include"
 // CHECK-GENTOO-4-9-3-32: "-internal-externc-isystem" "[[SYSROOT]]/usr/include"
 //
+// Test support for parsing Gentoo's gcc-config -- clang should parse the
+// /etc/env.d/gcc/config-x86_64-pc-linux-gnu file to find CURRENT gcc used.
+// Then should pick the multilibs from version 4.9.x specified in
+// /etc/env.d/gcc/x86_64-pc-linux-gnu-4.9.3.
+// RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
+// RUN:     -target x86_64-unknown-linux-gnu -stdlib=libstdc++ \
+// RUN:     --sysroot=%S/Inputs/gentoo_linux_gcc_4.9.x_tree \
+// RUN:     --gcc-toolchain="" \
+// RUN:   | FileCheck --check-prefix=CHECK-GENTOO-4-9-X %s
+//
+// CHECK-GENTOO-4-9-X: "{{.*}}clang{{.*}}" "-cc1"
+// CHECK-GENTOO-4-9-X: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
+// CHECK-GENTOO-4-9-X: "-isysroot" "[[SYSROOT:[^"]+]]"
+// CHECK-GENTOO-4-9-X: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3"
+// CHECK-GENTOO-4-9-X: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3/x86_64-pc-linux-gnu"
+// CHECK-GENTOO-4-9-X: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3/backward"
+// CHECK-GENTOO-4-9-X: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
+// CHECK-GENTOO-4-9-X: "-internal-isystem" "[[RESOURCE_DIR]]{{/|\\\\}}include"
+// CHECK-GENTOO-4-9-X: "-internal-externc-isystem" "[[SYSROOT]]/include"
+// CHECK-GENTOO-4-9-X: "-internal-externc-isystem" "[[SYSROOT]]/usr/include"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
+// RUN:     -target x86_64-unknown-linux-gnux32 -stdlib=libstdc++ \
+// RUN:     --sysroot=%S/Inputs/gentoo_linux_gcc_4.9.x_tree \
+// RUN:     --gcc-toolchain="" \
+// RUN:   | FileCheck --check-prefix=CHECK-GENTOO-4-9-X-X32 %s
+// CHECK-GENTOO-4-9-X-X32: "{{.*}}clang{{.*}}" "-cc1"
+// CHECK-GENTOO-4-9-X-X32: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
+// CHECK-GENTOO-4-9-X-X32: "-isysroot" "[[SYSROOT:[^"]+]]"
+// CHECK-GENTOO-4-9-X-X32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3"
+// CHECK-GENTOO-4-9-X-X32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3/x86_64-pc-linux-gnu/x32"
+// CHECK-GENTOO-4-9-X-X32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3/backward"
+// CHECK-GENTOO-4-9-X-X32: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
+// CHECK-GENTOO-4-9-X-X32: "-internal-isystem" "[[RESOURCE_DIR]]{{/|\\\\}}include"
+// CHECK-GENTOO-4-9-X-X32: "-internal-externc-isystem" "[[SYSROOT]]/include"
+// CHECK-GENTOO-4-9-X-X32: "-internal-externc-isystem" "[[SYSROOT]]/usr/include"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
+// RUN:     -target i386-unknown-linux-gnu -stdlib=libstdc++ \
+// RUN:     --sysroot=%S/Inputs/gentoo_linux_gcc_4.9.x_tree \
+// RUN:     --gcc-toolchain="" \
+// RUN:   | FileCheck --check-prefix=CHECK-GENTOO-4-9-X-32 %s
+// CHECK-GENTOO-4-9-X-32: "{{.*}}clang{{.*}}" "-cc1"
+// CHECK-GENTOO-4-9-X-32: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
+// CHECK-GENTOO-4-9-X-32: "-isysroot" "[[SYSROOT:[^"]+]]"
+// CHECK-GENTOO-4-9-X-32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3"
+// CHECK-GENTOO-4-9-X-32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3/x86_64-pc-linux-gnu/32"
+// CHECK-GENTOO-4-9-X-32: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4.9.3/backward"
+// CHECK-GENTOO-4-9-X-32: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
+// CHECK-GENTOO-4-9-X-32: "-internal-isystem" "[[RESOURCE_DIR]]{{/|\\\\}}include"
+// CHECK-GENTOO-4-9-X-32: "-internal-externc-isystem" "[[SYSROOT]]/include"
+// CHECK-GENTOO-4-9-X-32: "-internal-externc-isystem" "[[SYSROOT]]/usr/include"
+//
 // Check header search on Debian 6 / MIPS64
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN:     -target mips64-unknown-linux-gnuabi64 -stdlib=libstdc++ \
 // RUN:     --sysroot=%S/Inputs/debian_6_mips64_tree \
 // RUN:     --gcc-toolchain="" \
 // RUN:   | FileCheck --check-prefix=CHECK-MIPS64-GNUABI %s
 // CHECK-MIPS64-GNUABI: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 // CHECK-MIPS64-GNUABI: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"