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 non-GuixSD systems.

This patch makes slight adjustments over "clang-libc-search-path.patch" for
changes in clang 3.8.

--- cfe-3.8.0.src/lib/Driver/ToolChains.cpp
+++ cfe-3.8.0.src/lib/Driver/ToolChains.cpp
@@ -3661,6 +3661,9 @@
                          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 = DetectDistro(D, Arch);
 
   if (IsOpenSUSE(Distro) || IsUbuntu(Distro)) {
@@ -3702,6 +3705,7 @@
 
   if (IsOpenSUSE(Distro))
     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.
@@ -3771,14 +3775,12 @@
     addPathIfExists(D, D.Dir + "/../" + OSLibDir, Paths);
   }
 
-  addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
-  addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib/" + MultiarchTriple, Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib/../" + OSLibDir, Paths);
-
   // 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.
+#if 0
     addPathIfExists(D,
                     SysRoot + "/usr/lib/" + GCCInstallation.getTriple().str() +
                         "/../../" + OSLibDir,
@@ -3791,6 +3793,7 @@
                              BiarchSibling.gccSuffix(),
                       Paths);
     }
+#endif
 
     // See comments above on the multilib variant for details of why this is
     // included even from outside the sysroot.
@@ -3815,8 +3818,9 @@
   if (StringRef(D.Dir).startswith(SysRoot))
     addPathIfExists(D, D.Dir + "/../lib", Paths);
 
-  addPathIfExists(D, SysRoot + "/lib", Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
+  // 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);
 }
 
 bool Linux::HasNativeLLVMSupport() const { return true; }
 <http://www.gnu.org/licenses/>.

(define-module (gnu compression)
  #:use-module (guix gexp)
  #:use-module (guix ui)
  #:use-module ((gnu packages compression) #:hide (zip))
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (ice-9 match)
  #:export (compressor
            compressor?
            compressor-name
            compressor-extension
            compressor-command
            %compressors
            lookup-compressor))

;; Type of a compression tool.
(define-record-type <compressor>
  (compressor name extension command)
  compressor?
  (name       compressor-name)      ;string (e.g., "gzip")
  (extension  compressor-extension) ;string (e.g., ".lz")
  (command    compressor-command))  ;gexp (e.g., #~(list "/gnu/store/…/gzip"
                                    ;                    "-9n" ))

(define %compressors
  ;; Available compression tools.
  (list (compressor "gzip"  ".gz"
                    #~(list #+(file-append gzip "/bin/gzip") "-9n"))
        (compressor "lzip"  ".lz"
                    #~(list #+(file-append lzip "/bin/lzip") "-9"))
        (compressor "xz"    ".xz"
                    #~(append (list #+(file-append xz "/bin/xz")
                                    "-e")
                              (%xz-parallel-args)))
        (compressor "bzip2" ".bz2"
                    #~(list #+(file-append bzip2 "/bin/bzip2") "-9"))
        (compressor "zstd" ".zst"
                    ;; The default level 3 compresses better than gzip in a
                    ;; fraction of the time, while the highest level 19
                    ;; (de)compresses more slowly and worse than xz.
                    #~(list #+(file-append zstd "/bin/zstd") "-3"
                            (format #f "--threads=~a" (parallel-job-count))))
        (compressor "none" "" #f)))

(define (lookup-compressor name)
  "Return the compressor object called NAME.  Error out if it could not be
found."
  (or (find (match-lambda
              (($ <compressor> name*)
               (string=? name* name)))
            %compressors)
      (leave (G_ "~a: compressor not found~%") name)))
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