Clang attempts to guess file names based on the OS and distro (yes!),
but unfortunately, that doesn't work for us.

This patch makes it easy to insert libc's $libdir so that Clang passes the
correct absolute file name of crt1.o etc. to 'ld'.  It also disables all
the distro-specific stuff and removes the hard-coded FHS directory names
to make sure Clang also works on foreign distros.

diff --git a/lib/Driver/Distro.cpp b/lib/Driver/Distro.cpp
index 396d0bee..90e06613 100644
--- a/lib/Driver/Distro.cpp
+++ b/lib/Driver/Distro.cpp
@@ -19,6 +19,10 @@ using namespace clang::driver;
 using namespace clang;
 
 static Distro::DistroType DetectDistro(llvm::vfs::FileSystem &VFS) {
+  // The compiler should always behave the same, even when used via Guix on a
+  // foreign distro.
+  return Distro::UnknownDistro;
+
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> File =
       VFS.getBufferForFile("/etc/lsb-release");
   if (File) {
diff --git a/lib/Driver/ToolChains/Cuda.cpp b/lib/Driver/ToolChains/Cuda.cpp
index 57b8d434..57339f1a 100644
--- a/lib/Driver/ToolChains/Cuda.cpp
+++ b/lib/Driver/ToolChains/Cuda.cpp
@@ -68,6 +68,9 @@ CudaInstallationDetector::CudaInstallationDetector(
     const Driver &D, const llvm::Triple &HostTriple,
     const llvm::opt::ArgList &Args)
     : D(D) {
+  // Don't look for CUDA in /usr.
+  return;
+
   struct Candidate {
     std::string Path;
     bool StrictChecking;
diff --git a/lib/Driver/ToolChains/Linux.cpp b/lib/Driver/ToolChains/Linux.cpp
index 65ab9b2d..5ed28e0a 100644
--- a/lib/Driver/ToolChains/Linux.cpp
+++ b/lib/Driver/ToolChains/Linux.cpp
@@ -233,7 +233,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   PPaths.push_back(Twine(GCCInstallation.getParentLibPath() + "/../" +
                          GCCInstallation.getTriple().str() + "/bin")
                        .str());
-
+  // Comment out the distro-specific tweaks so that they don't bite when
+  // using Guix on a foreign distro.
+#if 0
   Distro Distro(D.getVFS());
 
   if (Distro.IsAlpineLinux() || Triple.isAndroid()) {
@@ -304,6 +306,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
 
   if (IsAndroid || Distro.IsOpenSUSE())
     ExtraOpts.push_back("--enable-new-dtags");
+#endif
 
   // The selection of paths to try here is designed to match the patterns which
   // the GCC driver itself uses, as this is part of the GCC-compatible driver.
@@ -366,6 +369,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
     }
   }
 
+#if 0
   // Similar to the logic for GCC above, if we currently running Clang inside
   // of the requested system root, add its parent library paths to
   // those searched.
@@ -411,6 +415,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   // Try walking via the GCC triple path in case of biarch or multiarch GCC
   // installations with strange symlinks.
   if (GCCInstallation.isValid()) {
+    // The following code would end up adding things like
+    // "/usr/lib/x86_64-unknown-linux-gnu/../../lib64" to the search path.
     addPathIfExists(D,
                     SysRoot + "/usr/lib/" + GCCInstallation.getTriple().str() +
                         "/../../" + OSLibDir,
@@ -446,9 +452,14 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   // directory ('Dir' below) or the ResourceDir.
   if (StringRef(D.Dir).startswith(SysRoot))
     addPathIfExists(D, D.Dir + "/../lib", Paths);
+#endif
+
+  // Add libc's lib/ directory to the search path, so that crt1.o, crti.o,
+  // and friends can be found.
+  addPathIfExists(D, "@GLIBC_LIBDIR@", Paths);
 
-  addPathIfExists(D, SysRoot + "/lib", Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
+  // Add GCC's lib/ directory so libstdc++.so can be found.
+  addPathIfExists(D, GCCInstallation.getParentLibPath(), Paths);
 }
 
 ToolChain::CXXStdlibType Linux::GetDefaultCXXStdlibType() const {
st-runner #$output))
          (test-begin #$name)

          ;; XXX: Shepherd reads the config file *before* binding its control
          ;; socket, so /var/run/shepherd/socket might not exist yet when the
          ;; &apos;marionette&apos; service is started.
          (test-assert &quot;shepherd socket ready&quot;
            (marionette-eval
             `(begin
                (use-modules (gnu services herd))
                (let loop ((i 10))
                  (cond ((file-exists? (%shepherd-socket-file))
                         #t)
                        ((&gt; i 0)
                         (sleep 1)
                         (loop (- i 1)))
                        (else
                         &apos;failure))))
             marionette))

          (test-assert &quot;Nix daemon running&quot;
            (marionette-eval
             &apos;(begin
                ;; Wait for nix-daemon to be up and running.
                (start-service &apos;nix-daemon)
                (zero? (system* (string-append #$nix &quot;/bin/nix&quot;)
                                &quot;--experimental-features&quot; &quot;nix-command&quot;
                                &quot;store&quot; &quot;ping&quot; &quot;--store&quot; &quot;daemon&quot;)))
             marionette))

          (test-end))))

  (gexp-&gt;derivation (string-append name &quot;-test&quot;) test))

(define %nix-os
  ;; Return operating system under test.
  (let ((base-os
         (simple-operating-system
          (service nix-service-type)
          (service dhcp-client-service-type))))
    (operating-system
      (inherit base-os)
      (packages (cons nix (operating-system-packages base-os))))))

(define %test-nix
  (system-test
   (name &quot;nix&quot;)
   (description &quot;Connect to a running nix-daemon&quot;)
   (value (run-nix-test name %nix-os))))

;;; package-management.scm ends here
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