[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) {
@@ -97,7 +131,8 @@ static bool findRISCVMultilibs(const Driver &D,
   return false;
 }
 
-static std::string computeBaseSysRoot(const Driver &D, bool IncludeTriple) {
+static std::string computeClangRuntimesSysRoot(const Driver &D,
+                                               bool IncludeTriple) {
   if (!D.SysRoot.empty())
     return D.SysRoot;
 
@@ -110,56 +145,123 @@ 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));
-    }
+// Only consider the GCC toolchain based on the values provided through the
+// `--gcc-toolchain` and `--gcc-install-dir` flags. The function below returns
+// whether the GCC toolchain was initialized successfully.
+bool BareMetal::initGCCInstallation(const llvm::Triple &Triple,
+                                    const llvm::opt::ArgList &Args) {
+  if (Args.getLastArg(options::OPT_gcc_toolchain) ||
+      Args.getLastArg(clang::driver::options::OPT_gcc_install_dir_EQ)) {
+    GCCInstallation.init(Triple, Args);
+    return GCCInstallation.isValid();
   }
+  return false;
 }
 
-/// 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";
+// This logic is adapted from RISCVToolChain.cpp as part of the ongoing effort
+// to merge RISCVToolChain into the Baremetal toolchain. It infers the presence
+// of a valid GCC toolchain by checking whether the `crt0.o` file exists in the
+// `bin/../<target-triple>/lib` directory.
+static bool detectGCCToolchainAdjacent(const Driver &D) {
+  SmallString<128> GCCDir;
+  llvm::sys::path::append(GCCDir, D.Dir, "..", D.getTargetTriple(),
+                          "lib/crt0.o");
+  return llvm::sys::fs::exists(GCCDir);
 }
 
-static bool isRISCVBareMetal(const llvm::Triple &Triple) {
-  if (!Triple.isRISCV())
-    return false;
+// If no sysroot is provided the driver will first attempt to infer it from the
+// values of `--gcc-install-dir` or `--gcc-toolchain`, which specify the
+// location of a GCC toolchain.
+// 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 {
+  // Use Baremetal::sysroot if it has already been set.
+  if (!SysRoot.empty())
+    return SysRoot;
+
+  // Use the sysroot specified via the `--sysroot` command-line flag, if
+  // provided.
+  const Driver &D = getDriver();
+  if (!D.SysRoot.empty())
+    return D.SysRoot;
 
-  if (Triple.getVendor() != llvm::Triple::UnknownVendor)
-    return false;
+  // Attempt to infer sysroot from a valid GCC installation.
+  // If no valid GCC installation, check for a GCC toolchain alongside Clang.
+  SmallString<128> inferredSysRoot;
+  if (IsGCCInstallationValid) {
+    llvm::sys::path::append(inferredSysRoot, GCCInstallation.getParentLibPath(),
+                            "..", GCCInstallation.getTriple().str());
+  } else if (detectGCCToolchainAdjacent(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(inferredSysRoot, D.Dir, "..", D.getTargetTriple());
+  }
+  // If a valid sysroot was inferred and exists, use it
+  if (!inferredSysRoot.empty() && llvm::sys::fs::exists(inferredSysRoot))
+    return std::string(inferredSysRoot);
 
-  if (Triple.getOS() != llvm::Triple::UnknownOS)
-    return false;
+  // Use the clang-runtimes path.
+  return computeClangRuntimesSysRoot(D, /*IncludeTriple*/ true);
+}
 
-  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 supports ARM,
+// AArch64, RISCV and PPC and of these 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) {
+  IsGCCInstallationValid = initGCCInstallation(Triple, Args);
+  std::string ComputedSysRoot = computeSysRoot();
+  if (IsGCCInstallationValid) {
+    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);
+    // Adding filepath for locating crt{begin,end}.o files.
+    Paths.push_back(GCCInstallation.getInstallPath().str());
+    // Adding filepath for locating crt0.o file.
+    Paths.push_back(ComputedSysRoot + "/lib");
+
+    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());
+  } 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
@@ -218,7 +320,7 @@ getMultilibConfigPath(const Driver &D, const llvm::Triple &Triple,
       return {};
     }
   } else {
-    MultilibPath = computeBaseSysRoot(D, /*IncludeTriple=*/false);
+    MultilibPath = computeClangRuntimesSysRoot(D, /*IncludeTriple=*/false);
     llvm::sys::path::append(MultilibPath, MultilibFilename);
   }
   return MultilibPath;
@@ -236,15 +338,15 @@ void BareMetal::findMultilibs(const Driver &D, const llvm::Triple &Triple,
   if (D.getVFS().exists(*MultilibPath)) {
     // If multilib.yaml is found, update sysroot so it doesn't use a target
     // specific suffix
-    SysRoot = computeBaseSysRoot(D, /*IncludeTriple=*/false);
+    SysRoot = computeClangRuntimesSysRoot(D, /*IncludeTriple=*/false);
     SmallVector<StringRef> CustomFlagMacroDefines;
     findMultilibsFromYAML(*this, D, *MultilibPath, Args, Result,
                           CustomFlagMacroDefines);
     SelectedMultilibs = Result.SelectedMultilibs;
     Multilibs = Result.Multilibs;
     MultilibMacroDefines.append(CustomFlagMacroDefines.begin(),
                                 CustomFlagMacroDefines.end());
-  } else if (isRISCVBareMetal(Triple)) {
+  } else if (isRISCVBareMetal(Triple) && !detectGCCToolchainAdjacent(D)) {
     if (findRISCVMultilibs(D, Triple, Args, Result)) {
       SelectedMultilibs = Result.SelectedMultilibs;
       Multilibs = Result.Multilibs;
@@ -265,8 +367,6 @@ 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 +394,10 @@ 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 +411,19 @@ void BareMetal::addClangTargetOptions(const ArgList &DriverArgs,
   CC1Args.push_back("-nostdsysteminc");
 }
 
+void BareMetal::addLibStdCxxIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
+  if (!IsGCCInstallationValid)
+    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 +454,23 @@ 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: {