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.

--- cfe-6.0.0.src/lib/Driver/ToolChains/Linux.cpp
+++ cfe-6.0.0.src/lib/Driver/ToolChains/Linux.cpp
@@ -207,7 +207,9 @@
   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()) {
@@ -255,6 +257,7 @@
 
   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.
@@ -329,14 +332,12 @@
     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,
@@ -349,6 +350,7 @@
                              BiarchSibling.gccSuffix(),
                       Paths);
     }
+#endif
 
     // See comments above on the multilib variant for details of why this is
     // included even from outside the sysroot.
@@ -373,8 +375,9 @@
   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; }
61501e9e8fe59aac6'>linux-libre</a>/<a href='/guix/log/gnu/packages/aux-files/linux-libre/5.10-x86_64.conf?id=79bd3c685f83239f385727661501e9e8fe59aac6'>5.10-x86_64.conf</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/aux-files/linux-libre/5.10-x86_64.conf?id=79bd3c685f83239f385727661501e9e8fe59aac6&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-02-19 01:00:01 +0100'>2023-02-19</span></td><td><a href='/guix/commit/gnu/packages/aux-files/linux-libre/5.10-x86_64.conf?id=e701f67246680c81dd111cf7136b936bf7d8718b'>gnu: linux-libre: Consistently provide the drop_monitor module.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is needed by, e.g., &lt;https://github.com/nhorman/dropwatch&gt;.
Build it as a module everywhere for consistency.

* gnu/packages/aux-files/linux-libre/4.14-i686.conf:
Set CONFIG_NET_DROP_MONITOR=m.
* gnu/packages/aux-files/linux-libre/4.14-x86_64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/4.19-i686.conf: Likewise.
* gnu/packages/aux-files/linux-libre/4.19-x86_64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.10-arm.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.10-arm64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.10-i686.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.10-x86_64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.15-arm.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.15-arm64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.15-i686.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.15-x86_64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.4-arm.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.4-arm64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.4-i686.conf: Likewise.
* gnu/packages/aux-files/linux-libre/5.4-x86_64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/6.1-arm.conf: Likewise.
* gnu/packages/aux-files/linux-libre/6.1-arm64.conf: Likewise.
* gnu/packages/aux-files/linux-libre/6.1-i686.conf: Likewise.
* gnu/packages/aux-files/linux-libre/6.1-x86_64.conf: Likewise.

Reported by mirai in #guix.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>