gnu: clang@11, clang@12: Do not refer to /lib on foreign distros.

Partly fixes <https://issues.guix.gnu.org/51088>.

* gnu/packages/patches/clang-11.0-libc-search-path.patch: Update.
* gnu/packages/patches/clang-12.0-libc-search-path.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/llvm.scm (clang-12): Use it.

gnu/local.mk

@@ -936,6 +936,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/clang-9.0-libc-search-path.patch		\
   %D%/packages/patches/clang-10.0-libc-search-path.patch	\
   %D%/packages/patches/clang-11.0-libc-search-path.patch	\
+  %D%/packages/patches/clang-12.0-libc-search-path.patch	\
   %D%/packages/patches/clang-runtime-asan-build-fixes.patch	\
   %D%/packages/patches/clang-runtime-esan-build-fixes.patch	\
   %D%/packages/patches/clang-runtime-9-libsanitizer-mode-field.patch	\

gnu/packages/llvm.scm

@@ -547,7 +547,7 @@ of programming tools as well as libraries with equivalent functionality.")
 (define-public clang-12
   (clang-from-llvm llvm-12 clang-runtime-12
                    "0px4gl27az6cdz6adds89qzdwb1cqpjsfvrldbz9qvpmphrj34bf"
-                   #:patches '("clang-11.0-libc-search-path.patch")
+                   #:patches '("clang-12.0-libc-search-path.patch")
                    #:tools-extra
                    (origin
                      (method url-fetch)

gnu/packages/patches/clang-11.0-libc-search-path.patch

@@ -4,48 +4,47 @@ 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-Guix systems.
+to make sure Clang also works on foreign distros.
 
-diff --git a/lib/Driver/ToolChains/Gnu.cpp b/lib/Driver/ToolChains/Gnu.cpp
+diff --git a/lib/Driver/Distro.cpp b/lib/Driver/Distro.cpp
---- a/lib/Driver/ToolChains/Gnu.cpp
+index 4d58ad1a..6f638eca 100644
-+++ b/lib/Driver/ToolChains/Gnu.cpp
+--- a/lib/Driver/Distro.cpp
-@@ -2797,7 +2797,7 @@ void Generic_GCC::AddMultilibPaths(const Driver &D,
++++ b/lib/Driver/Distro.cpp
-     // the cross. Note that GCC does include some of these directories in some
+@@ -21,6 +21,10 @@ using namespace clang;
-     // configurations but this seems somewhere between questionable and simply
-     // a bug.
--    if (StringRef(LibPath).startswith(SysRoot)) {
-+    if (0) {
-       addPathIfExists(D, LibPath + "/" + MultiarchTriple, Paths);
-       addPathIfExists(D, LibPath + "/../" + OSLibDir, Paths);
-     }
-@@ -2811,6 +2811,10 @@ void Generic_GCC::AddMultiarchPaths(const Driver &D,
-   // 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,
-@@ -2823,6 +2827,7 @@ void Generic_GCC::AddMultiarchPaths(const Driver &D,
-           D, GCCInstallation.getInstallPath() + BiarchSibling.gccSuffix(),
-                       Paths);
-     }
-+#endif // Guix
  
-     // See comments above on the multilib variant for details of why this is
+ static Distro::DistroType DetectDistro(llvm::vfs::FileSystem &VFS,
-     // included even from outside the sysroot.
+                                        const llvm::Triple &TargetOrHost) {
++  // The compiler should always behave the same, even when used via Guix on a
++  // foreign distro.
++  return Distro::UnknownDistro;
++
+   // If we don't target Linux, no need to check the distro. This saves a few
+   // OS calls.
+   if (!TargetOrHost.isOSLinux())
+diff --git a/lib/Driver/ToolChains/Cuda.cpp b/lib/Driver/ToolChains/Cuda.cpp
+index 110a0bca..42b9f7b7 100644
+--- a/lib/Driver/ToolChains/Cuda.cpp
++++ b/lib/Driver/ToolChains/Cuda.cpp
+@@ -67,6 +67,9 @@ 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 18035047..ace8f443 100644
 --- a/lib/Driver/ToolChains/Linux.cpp
 +++ b/lib/Driver/ToolChains/Linux.cpp
 @@ -219,6 +219,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
  
    Generic_GCC::PushPPaths(PPaths);
  
-+// Comment out the distro-specific tweaks so that they don't bite when
++  // Comment out the distro-specific tweaks so that they don't bite when
-+// using Guix on a foreign distro.
++  // using Guix on a foreign distro.
 +#if 0
    Distro Distro(D.getVFS(), Triple);
  
@@ -54,36 +53,32 @@ diff --git a/lib/Driver/ToolChains/Linux.cpp b/lib/Driver/ToolChains/Linux.cpp
  
    if (IsAndroid || Distro.IsOpenSUSE())
      ExtraOpts.push_back("--enable-new-dtags");
-+#endif	// Guix
++#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.
-@@ -310,6 +314,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+@@ -297,6 +301,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-   addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
+ 
-   addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
+   Generic_GCC::AddMultilibPaths(D, SysRoot, OSLibDir, MultiarchTriple, Paths);
  
-+// This requires the commented distro tweaks above.
 +#if 0
-   if (IsAndroid) {
+   // Similar to the logic for GCC above, if we currently running Clang inside
-     // Android sysroots contain a library directory for each supported OS
+   // of the requested system root, add its parent library paths to
-     // version as well as some unversioned libraries in the usual multiarch
+   // those searched.
-@@ -338,6 +344,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+@@ -348,9 +353,14 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-     addPathIfExists(D, SysRoot + "/" + OSLibDir + "/" + ABIName, Paths);
+   // directory ('Dir' below) or the ResourceDir.
-     addPathIfExists(D, SysRoot + "/usr/" + OSLibDir + "/" + ABIName, Paths);
-   }
-+#endif // Guix
- 
-   Generic_GCC::AddMultiarchPaths(D, SysRoot, OSLibDir, Paths);
- 
-@@ -349,8 +356,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
    if (StringRef(D.Dir).startswith(SysRoot))
      addPathIfExists(D, D.Dir + "/../lib", Paths);
- 
++#endif
--  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);
+ 
+-  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 {

gnu/packages/patches/clang-12.0-libc-search-path.patch

@@ -0,0 +1,84 @@
+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 ee4fe841..f0313bbe 100644
+--- a/lib/Driver/Distro.cpp
++++ b/lib/Driver/Distro.cpp
+@@ -93,6 +93,10 @@ static Distro::DistroType DetectLsbRelease(llvm::vfs::FileSystem &VFS) {
+ }
+ 
+ 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;
++
+   Distro::DistroType Version = Distro::UnknownDistro;
+ 
+   // Newer freedesktop.org's compilant systemd-based systems
+diff --git a/lib/Driver/ToolChains/Cuda.cpp b/lib/Driver/ToolChains/Cuda.cpp
+index d14776c5..88bc3ccd 100644
+--- a/lib/Driver/ToolChains/Cuda.cpp
++++ b/lib/Driver/ToolChains/Cuda.cpp
+@@ -119,6 +119,9 @@ 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 9663a739..107f96d6 100644
+--- a/lib/Driver/ToolChains/Linux.cpp
++++ b/lib/Driver/ToolChains/Linux.cpp
+@@ -223,6 +223,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+ 
+   Generic_GCC::PushPPaths(PPaths);
+ 
++  // 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(), Triple);
+ 
+   if (Distro.IsAlpineLinux() || Triple.isAndroid()) {
+@@ -288,6 +291,7 @@ 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.
+@@ -301,6 +305,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+ 
+   Generic_GCC::AddMultilibPaths(D, SysRoot, OSLibDir, MultiarchTriple, Paths);
+ 
++#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.
+@@ -352,9 +357,14 @@ 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 {