[Driver] Teach Barmetal toolchain about GCC installation

This patch introduces the baretmetal toolchain object about GCC Installation.
Currently, if `--gcc-installation` ot `--gcc-install-dir` options are passed on
commandline, then sysroot will be formed from there if paths will be valid.
Otherwise, it will be fallback to as it already existed in the Baremetal
toolchaibn object. Moreover, support for adding include paths for libstd
C++ library is added as well.

Additionally, the restriction to always use integrated assembler is removed
because with valid gcc installation, gnu assembler can be invoked as well.

This patch currently adds and modifies arm related test only. The riscv specific
test will be added in the last PR when driver code related to calling of
RISCVToolchain object will be removed. Currently in this PR, there is no way to
test riscv target.

RFC:
https://discourse.llvm.org/t/merging-riscvtoolchain-and-baremetal-toolchains/75524

Change-Id: Ibaeb569cf7e2cee03c022aa9ecd1abe29d5c30d4

Author: Garvit Gupta

clang/docs/Toolchain.rst

@@ -347,3 +347,8 @@ workarounds for issues discovered in libstdc++, and these are removed
 as fixed libstdc++ becomes sufficiently old.
 
 You can instruct Clang to use libstdc++ with the ``-stdlib=libstdc++`` flag.
+
+GCC Installation
+=================
+Users can point to their GCC installation by using the ``-gcc-toolchain`` or by
+using ``-gcc-install-dir`` flag.

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -830,6 +830,9 @@ def note_drv_available_multilibs : Note<
   "available multilibs are:%0">;
 def err_drv_multilib_custom_error : Error<
   "multilib configuration error: %0">;
+def warn_drv_multilib_not_available_for_target: Warning<
+  "no multilib structure encoded for Arm, Aarch64 and PPC targets">,
+  InGroup<DiagGroup<"multilib-not-found">>;
 
 def err_drv_experimental_crel : Error<
   "-Wa,--allow-experimental-crel must be specified to use -Wa,--crel. "

clang/lib/Driver/ToolChains/BareMetal.cpp

@@ -33,6 +33,40 @@ using namespace clang::driver;
 using namespace clang::driver::tools;
 using namespace clang::driver::toolchains;
 
+/// Is the triple {aarch64.aarch64_be}-none-elf?
+static bool isAArch64BareMetal(const llvm::Triple &Triple) {
+  if (Triple.getArch() != llvm::Triple::aarch64 &&
+      Triple.getArch() != llvm::Triple::aarch64_be)
+    return false;
+
+  if (Triple.getVendor() != llvm::Triple::UnknownVendor)
+    return false;
+
+  if (Triple.getOS() != llvm::Triple::UnknownOS)
+    return false;
+
+  return Triple.getEnvironmentName() == "elf";
+}
+
+static bool isRISCVBareMetal(const llvm::Triple &Triple) {
+  if (!Triple.isRISCV())
+    return false;
+
+  if (Triple.getVendor() != llvm::Triple::UnknownVendor)
+    return false;
+
+  if (Triple.getOS() != llvm::Triple::UnknownOS)
+    return false;
+
+  return Triple.getEnvironmentName() == "elf";
+}
+
+/// Is the triple powerpc[64][le]-*-none-eabi?
+static bool isPPCBareMetal(const llvm::Triple &Triple) {
+  return Triple.isPPC() && Triple.getOS() == llvm::Triple::UnknownOS &&
+         Triple.getEnvironment() == llvm::Triple::EABI;
+}
+
 static bool findRISCVMultilibs(const Driver &D,
                                const llvm::Triple &TargetTriple,
                                const ArgList &Args, DetectedMultilibs &Result) {
@@ -110,56 +144,99 @@ static std::string computeBaseSysRoot(const Driver &D, bool IncludeTriple) {
   return std::string(SysRootDir);
 }
 
-BareMetal::BareMetal(const Driver &D, const llvm::Triple &Triple,
-                     const ArgList &Args)
-    : ToolChain(D, Triple, Args),
-      SysRoot(computeBaseSysRoot(D, /*IncludeTriple=*/true)) {
-  getProgramPaths().push_back(getDriver().Dir);
-
-  findMultilibs(D, Triple, Args);
-  SmallString<128> SysRoot(computeSysRoot());
-  if (!SysRoot.empty()) {
-    for (const Multilib &M : getOrderedMultilibs()) {
-      SmallString<128> Dir(SysRoot);
-      llvm::sys::path::append(Dir, M.osSuffix(), "lib");
-      getFilePaths().push_back(std::string(Dir));
-      getLibraryPaths().push_back(std::string(Dir));
-    }
-  }
+static bool hasGCCToolChainAlongSideClang(const Driver &D) {
+  SmallString<128> GCCDir;
+  llvm::sys::path::append(GCCDir, D.Dir, "..", D.getTargetTriple(),
+                          "lib/crt0.o");
+  return llvm::sys::fs::exists(GCCDir);
 }
 
-/// Is the triple {aarch64.aarch64_be}-none-elf?
-static bool isAArch64BareMetal(const llvm::Triple &Triple) {
-  if (Triple.getArch() != llvm::Triple::aarch64 &&
-      Triple.getArch() != llvm::Triple::aarch64_be)
-    return false;
+// Users can specify their GCC toolchain using `-gcc-install-dir` or
+// `--gcc-toolchain`. If no sysroot is explicitly provided, the driver will
+// attempt to infer it from the values of the above flags.
+//
+// If neither flag is used, the sysroot defaults to either:
+//    - `bin/../<target-triple>`
+//    - `bin/../lib/clang-runtimes/<target-triple>`
+//
+// To use the `clang-runtimes` path, ensure that `../<target-triple>/lib/crt0.o`
+// does not exist relative to the driver.
+std::string BareMetal::computeSysRoot() const {
+  if (!SysRoot.empty())
+    return SysRoot;
 
-  if (Triple.getVendor() != llvm::Triple::UnknownVendor)
-    return false;
+  const Driver &D = getDriver();
+  if (!D.SysRoot.empty())
+    return D.SysRoot;
 
-  if (Triple.getOS() != llvm::Triple::UnknownOS)
-    return false;
+  // Verify the GCC installation from -gcc-install-dir, --gcc-toolchain, or
+  // alongside clang. If valid, form the sysroot. Otherwise, check
+  // lib/clang-runtimes above the driver.
+  SmallString<128> SysRootDir;
+  if (GCCInstallation.isValid()) {
+    StringRef LibDir = GCCInstallation.getParentLibPath();
+    StringRef TripleStr = GCCInstallation.getTriple().str();
+    llvm::sys::path::append(SysRootDir, LibDir, "..", TripleStr);
+  } else if (hasGCCToolChainAlongSideClang(D)) {
+    // Use the triple as provided to the driver. Unlike the parsed triple
+    // this has not been normalized to always contain every field.
+    llvm::sys::path::append(SysRootDir, D.Dir, "..", D.getTargetTriple());
+  }
 
-  return Triple.getEnvironmentName() == "elf";
+  if (llvm::sys::fs::exists(SysRootDir))
+    return std::string(SysRootDir);
+  return computeBaseSysRoot(D, /*IncludeTriple*/ true);
 }
 
-static bool isRISCVBareMetal(const llvm::Triple &Triple) {
-  if (!Triple.isRISCV())
-    return false;
-
-  if (Triple.getVendor() != llvm::Triple::UnknownVendor)
-    return false;
-
-  if (Triple.getOS() != llvm::Triple::UnknownOS)
-    return false;
-
-  return Triple.getEnvironmentName() == "elf";
+static void addMultilibsFilePaths(const Driver &D, const MultilibSet &Multilibs,
+                                  const Multilib &Multilib,
+                                  StringRef InstallPath,
+                                  ToolChain::path_list &Paths) {
+  if (const auto &PathsCallback = Multilibs.filePathsCallback())
+    for (const auto &Path : PathsCallback(Multilib))
+      addPathIfExists(D, InstallPath + Path, Paths);
 }
 
-/// Is the triple powerpc[64][le]-*-none-eabi?
-static bool isPPCBareMetal(const llvm::Triple &Triple) {
-  return Triple.isPPC() && Triple.getOS() == llvm::Triple::UnknownOS &&
-         Triple.getEnvironment() == llvm::Triple::EABI;
+// GCC mutltilibs will only work for those targets that have their multlib
+// structure encoded into GCCInstallation. Baremetal toolchain support ARM,
+// AArch64, RISCV and PPC and of them only RISCV have GCC multilibs hardcoded
+// in GCCInstallation.
+BareMetal::BareMetal(const Driver &D, const llvm::Triple &Triple,
+                     const ArgList &Args)
+    : Generic_ELF(D, Triple, Args) {
+  GCCInstallation.init(Triple, Args);
+  SysRoot = computeSysRoot();
+  if (GCCInstallation.isValid()) {
+    if (!isRISCVBareMetal(Triple))
+      D.Diag(clang::diag::warn_drv_multilib_not_available_for_target);
+    Multilibs = GCCInstallation.getMultilibs();
+    SelectedMultilibs.assign({GCCInstallation.getMultilib()});
+    path_list &Paths = getFilePaths();
+    // Add toolchain/multilib specific file paths.
+    addMultilibsFilePaths(D, Multilibs, SelectedMultilibs.back(),
+                          GCCInstallation.getInstallPath(), Paths);
+    getFilePaths().push_back(GCCInstallation.getInstallPath().str());
+    ToolChain::path_list &PPaths = getProgramPaths();
+    // Multilib cross-compiler GCC installations put ld in a triple-prefixed
+    // directory off of the parent of the GCC installation.
+    PPaths.push_back(Twine(GCCInstallation.getParentLibPath() + "/../" +
+                           GCCInstallation.getTriple().str() + "/bin")
+                         .str());
+    PPaths.push_back((GCCInstallation.getParentLibPath() + "/../bin").str());
+    getFilePaths().push_back(SysRoot + "/lib");
+  } else {
+    getProgramPaths().push_back(getDriver().Dir);
+    findMultilibs(D, Triple, Args);
+    const SmallString<128> SysRootDir(computeSysRoot());
+    if (!SysRootDir.empty()) {
+      for (const Multilib &M : getOrderedMultilibs()) {
+        SmallString<128> Dir(SysRootDir);
+        llvm::sys::path::append(Dir, M.osSuffix(), "lib");
+        getFilePaths().push_back(std::string(Dir));
+        getLibraryPaths().push_back(std::string(Dir));
+      }
+    }
+  }
 }
 
 static void
@@ -244,7 +321,7 @@ void BareMetal::findMultilibs(const Driver &D, const llvm::Triple &Triple,
     Multilibs = Result.Multilibs;
     MultilibMacroDefines.append(CustomFlagMacroDefines.begin(),
                                 CustomFlagMacroDefines.end());
-  } else if (isRISCVBareMetal(Triple)) {
+  } else if (isRISCVBareMetal(Triple) && !hasGCCToolChainAlongSideClang(D)) {
     if (findRISCVMultilibs(D, Triple, Args, Result)) {
       SelectedMultilibs = Result.SelectedMultilibs;
       Multilibs = Result.Multilibs;
@@ -265,8 +342,6 @@ Tool *BareMetal::buildStaticLibTool() const {
   return new tools::baremetal::StaticLibTool(*this);
 }
 
-std::string BareMetal::computeSysRoot() const { return SysRoot; }
-
 BareMetal::OrderedMultilibs BareMetal::getOrderedMultilibs() const {
   // Get multilibs in reverse order because they're ordered most-specific last.
   if (!SelectedMultilibs.empty())
@@ -294,10 +369,10 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   if (std::optional<std::string> Path = getStdlibIncludePath())
     addSystemInclude(DriverArgs, CC1Args, *Path);
 
-  const SmallString<128> SysRoot(computeSysRoot());
-  if (!SysRoot.empty()) {
+  const SmallString<128> SysRootDir(computeSysRoot());
+  if (!SysRootDir.empty()) {
     for (const Multilib &M : getOrderedMultilibs()) {
-      SmallString<128> Dir(SysRoot);
+      SmallString<128> Dir(SysRootDir);
       llvm::sys::path::append(Dir, M.includeSuffix());
       llvm::sys::path::append(Dir, "include");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());
@@ -311,6 +386,19 @@ void BareMetal::addClangTargetOptions(const ArgList &DriverArgs,
   CC1Args.push_back("-nostdsysteminc");
 }
 
+void BareMetal::addLibStdCxxIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
+  if (!GCCInstallation.isValid())
+    return;
+  const GCCVersion &Version = GCCInstallation.getVersion();
+  StringRef TripleStr = GCCInstallation.getTriple().str();
+  const Multilib &Multilib = GCCInstallation.getMultilib();
+  addLibStdCXXIncludePaths(computeSysRoot() + "/include/c++/" + Version.Text,
+                           TripleStr, Multilib.includeSuffix(), DriverArgs,
+                           CC1Args);
+}
+
 void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                              ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdinc, options::OPT_nostdlibinc,
@@ -341,23 +429,23 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
   };
 
   switch (GetCXXStdlibType(DriverArgs)) {
-    case ToolChain::CST_Libcxx: {
-      SmallString<128> P(D.Dir);
-      llvm::sys::path::append(P, "..", "include");
-      AddCXXIncludePath(P);
-      break;
-    }
-    case ToolChain::CST_Libstdcxx:
-      // We only support libc++ toolchain installation.
-      break;
+  case ToolChain::CST_Libcxx: {
+    SmallString<128> P(D.Dir);
+    llvm::sys::path::append(P, "..", "include");
+    AddCXXIncludePath(P);
+    break;
+  }
+  case ToolChain::CST_Libstdcxx:
+    addLibStdCxxIncludePaths(DriverArgs, CC1Args);
+    break;
   }
 
-  std::string SysRoot(computeSysRoot());
-  if (SysRoot.empty())
+  std::string SysRootDir(computeSysRoot());
+  if (SysRootDir.empty())
     return;
 
   for (const Multilib &M : getOrderedMultilibs()) {
-    SmallString<128> Dir(SysRoot);
+    SmallString<128> Dir(SysRootDir);
     llvm::sys::path::append(Dir, M.gccSuffix());
     switch (GetCXXStdlibType(DriverArgs)) {
     case ToolChain::CST_Libcxx: {

clang/lib/Driver/ToolChains/BareMetal.h

@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_BAREMETAL_H
 #define LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_BAREMETAL_H
 
+#include "ToolChains/Gnu.h"
 #include "clang/Driver/Tool.h"
 #include "clang/Driver/ToolChain.h"
 
@@ -19,7 +20,7 @@ namespace driver {
 
 namespace toolchains {
 
-class LLVM_LIBRARY_VISIBILITY BareMetal : public ToolChain {
+class LLVM_LIBRARY_VISIBILITY BareMetal : public Generic_ELF {
 public:
   BareMetal(const Driver &D, const llvm::Triple &Triple,
             const llvm::opt::ArgList &Args);
@@ -35,7 +36,6 @@ class LLVM_LIBRARY_VISIBILITY BareMetal : public ToolChain {
   Tool *buildStaticLibTool() const override;
 
 public:
-  bool useIntegratedAs() const override { return true; }
   bool isBareMetal() const override { return true; }
   bool isCrossCompiling() const override { return true; }
   bool HasNativeLLVMSupport() const override { return true; }
@@ -48,6 +48,11 @@ class LLVM_LIBRARY_VISIBILITY BareMetal : public ToolChain {
 
   StringRef getOSLibName() const override { return "baremetal"; }
 
+  UnwindTableLevel
+  getDefaultUnwindTableLevel(const llvm::opt::ArgList &Args) const override {
+    return UnwindTableLevel::None;
+  }
+
   RuntimeLibType GetDefaultRuntimeLibType() const override {
     return ToolChain::RLT_CompilerRT;
   }
@@ -67,6 +72,9 @@ class LLVM_LIBRARY_VISIBILITY BareMetal : public ToolChain {
   void AddClangCXXStdlibIncludeArgs(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
+  void
+  addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                           llvm::opt::ArgStringList &CC1Args) const override;
   std::string computeSysRoot() const override;
   SanitizerMask getSupportedSanitizers() const override;
 
@@ -104,7 +112,7 @@ class LLVM_LIBRARY_VISIBILITY StaticLibTool : public Tool {
 
 class LLVM_LIBRARY_VISIBILITY Linker final : public Tool {
 public:
-  Linker(const ToolChain &TC) : Tool("baremetal::Linker", "ld.lld", TC) {}
+  Linker(const ToolChain &TC) : Tool("baremetal::Linker", "linker", TC) {}
   bool isLinkJob() const override { return true; }
   bool hasIntegratedCPP() const override { return false; }
   void ConstructJob(Compilation &C, const JobAction &JA,

clang/test/Driver/Inputs/basic_aarch64_gcc_tree/aarch64-none-elf/include/c++/8.2.1/.keep

@@ -0,0 +1 @@
+#!/bin/true