[clang] [Driver] Add support for GCC installation detection in Baremetal toolchain (PR #121829)

[Peter Smith via cfe-commits]

================
@@ -110,56 +145,113 @@ 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));
-    }
-  }
+// 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);
 }
 
-/// 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 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 (GCCInstallation.isValid()) {
+    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 (Triple.getOS() != llvm::Triple::UnknownOS)
-    return false;
+  // If a valid path was inferred and exists, use it
+  if (!inferredSysRoot.empty() && llvm::sys::fs::exists(inferredSysRoot))
+    return std::string(inferredSysRoot);
 
-  return Triple.getEnvironmentName() == "elf";
+  // Use the clang-runtimes path.
+  return computeClangRuntimesSysRoot(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 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) {
+  GCCInstallation.init(Triple, Args);
----------------
smithp35 wrote:

Thanks for the update. I'll rebuild the toolchain to check everything is still working.

https://github.com/llvm/llvm-project/pull/121829