[Clang] Fix Hurd toolchain class hierarchy

[aganea]

Summary

As noted in PR45061, a two-stage ThinLTO build fails the clang/test/Driver/hurd.c test because of a static_cast here which wrongly converts an instance of clang::driver::toolchains::Hurd into that of clang::driver::toolchains::Linux. ThinLTO will later devirtualize the ToolChain.getDynamicLinker(Args); call and use Linux::getDynamicLinker() instead, causing the test to generate a wrong -dynamic-linker linker flag (/lib/ld-linux.so.2 instead of /lib/ld.so)

Ideally, and because of the static_cast mentioned above, maybe gnutools::Linker should take a const Generic_ELF & instance, not a const ToolChain &. But that causes other issues and could be done later.

[aganea]

@hans, do you think this could be included in 10.0?

[aganea]

Fix clang-formatting.

[aganea]

The patch did not make sense conceptually. Hurd is not Linux. I think now it makes more sense.

[hans]

In D75373#1898620, @aganea wrote:

@hans, do you think this could be included in 10.0?

I think it's too late in the process for this, maybe it can be merged for 10.0.1.

[kristina]

In D75373#1900237, @aganea wrote:

The patch did not make sense conceptually. Hurd is not Linux. I think now it makes more sense.

Yes this seems to make more sense now. LGTM.

clang/lib/Driver/ToolChains/Hurd.h

 //===--- Hurd.h - Hurd ToolChain Implementations ----------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_Hurd_H
 #define LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_Hurd_H
 
 #include "Gnu.h"
+#include "Linux.h"
 #include "clang/Driver/ToolChain.h"
 
 namespace clang {
 namespace driver {
 namespace toolchains {
 
-class LLVM_LIBRARY_VISIBILITY Hurd : public Generic_ELF {
+class LLVM_LIBRARY_VISIBILITY Hurd : public Linux {
 public:
   Hurd(const Driver &D, const llvm::Triple &Triple,
        const llvm::opt::ArgList &Args);
 
   bool HasNativeLLVMSupport() const override;
 
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
 
-  virtual std::string computeSysRoot() const;
+  std::string computeSysRoot() const override;
 
-  virtual std::string getDynamicLinker(const llvm::opt::ArgList &Args) const;
+  std::string getDynamicLinker(const llvm::opt::ArgList &Args) const override;
 
   std::vector<std::string> ExtraOpts;
 
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
 
   std::string getMultiarchTriple(const Driver &D,

clang/lib/Driver/ToolChains/Hurd.cpp

static StringRef getOSLibDir(const llvm::Triple &Triple, const ArgList &Args) {
   // GCCInstallationDetector, but that is a more significant refactoring.
 
   if (Triple.getArch() == llvm::Triple::x86)
     return "lib32";
 
   return Triple.isArch32Bit() ? "lib" : "lib64";
 }
 
 Hurd::Hurd(const Driver &D, const llvm::Triple &Triple,
            const ArgList &Args)
-    : Generic_ELF(D, Triple, Args) {
+    : Linux(D, Triple, Args) {
   std::string SysRoot = computeSysRoot();
   path_list &Paths = getFilePaths();
 
   const std::string OSLibDir = getOSLibDir(Triple, Args);
   const std::string MultiarchTriple = getMultiarchTriple(D, Triple, SysRoot);
 
 #ifdef ENABLE_LINKER_BUILD_ID
   ExtraOpts.push_back("--build-id");