Explicitly Craft a Path to Compiler-RT Builtins on Bare Metal Targets

[CodaFi]

Summary

D33259 hard-coded a linker flag relative to a linker library search path that should have allowed it to find libclang_rt.builtins-$ARCH.a under the resource directory automatically. Unfortunately, both the flag and the search path are incorrect, which leads to workarounds like double-suffixes in linker invocations.

The bare metal toolchain now uses a more standard hook to get the right arch-specific compiler-rt, and constructs a full path relative to the resource directory for the linker input.

[CodaFi]

@mehdi_amini @kristina Ping.

[CodaFi]

+@phosek Who seems to be the last significant contributor to this file.

[phosek]

clang/lib/Driver/ToolChains/BareMetal.cpp

173

Would it be possible to support the per-target runtimes directory layout as well?

[CodaFi]

clang/lib/Driver/ToolChains/BareMetal.cpp

173

Does that make sense in the context of bare metal triples? My understanding of the layout of the resource directory for these targets is hazy, but I was under the impression that each target architecture having its own namespaced copy of compiler-rt in <RESOURCE_DIR>/lib *is* how we do per-target runtimes.

[phosek]

clang/lib/Driver/ToolChains/BareMetal.cpp

173

The per-target runtimes directory layout always expects a triple, i.e. <RESOURCE_DIR>/lib/<triple>. In case of bare metal, the triple would be e.g. armv6m-none-eabi.

clang/lib/Driver/ToolChains/BareMetal.h

public:
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args,
                              Action::OffloadKind DeviceOffloadKind) const override;
   void AddClangCXXStdlibIncludeArgs(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
-  void AddLinkRuntimeLib(const llvm::opt::ArgList &Args,
-                         llvm::opt::ArgStringList &CmdArgs) const;
+
+  std::string getCompilerRT(const llvm::opt::ArgList &Args,
+                            StringRef Component,
+                            FileType Type = ToolChain::FT_Static) const override;
 };
 
 } // namespace toolchains
 
 namespace tools {
 namespace baremetal {
 
 class LLVM_LIBRARY_VISIBILITY Linker : public Tool {

clang/lib/Driver/ToolChains/BareMetal.cpp

void BareMetal::AddCXXStdlibLibArgs(const ArgList &Args,
   case ToolChain::CST_Libstdcxx:
     CmdArgs.push_back("-lstdc++");
     CmdArgs.push_back("-lsupc++");
     break;
   }
   CmdArgs.push_back("-lunwind");
 }
 
-void BareMetal::AddLinkRuntimeLib(const ArgList &Args,
-                                  ArgStringList &CmdArgs) const {
-  CmdArgs.push_back(Args.MakeArgString("-lclang_rt.builtins-" +
-                                       getTriple().getArchName() + ".a"));
+std::string BareMetal::getCompilerRT(const llvm::opt::ArgList &Args,
+                                     StringRef Component,
+                                     FileType Type) const {
+  SmallString<128> Path(getDriver().ResourceDir);
+  const char *Suffix;
+  switch (Type) {
+    case ToolChain::FT_Object:
+      Suffix = ".o";
+      break;
+    case ToolChain::FT_Static:
+      Suffix = ".a";
+      break;
+    case ToolChain::FT_Shared:
+      Suffix = ".so";
+      break;
+  }
+
+  // Builds of compiler-rt on bare-metal targets are specialized by specific
+  // architecture rather than architecture classes.  We grab the triple's
+  // architecture explicitly so we don't just link the generic thumb-mode
+  // versions of these libraries.
+  auto Arch = getTriple().getArchName();
+  llvm::sys::path::append(
+      Path, "lib", Twine("libclang_rt." + Component + "-" + Arch + Suffix));
+  return Path.str();
 }
 
 void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                      const InputInfo &Output,
                                      const InputInfoList &Inputs,
                                      const ArgList &Args,
                                      const char *LinkingOutput) const {
   ArgStringList CmdArgs;
Args.AddAllArgs(CmdArgs, {options::OPT_L, options::OPT_T_Group,
                             options::OPT_Z_Flag, options::OPT_r});
 
   if (TC.ShouldLinkCXXStdlib(Args))
     TC.AddCXXStdlibLibArgs(Args, CmdArgs);
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     CmdArgs.push_back("-lc");
     CmdArgs.push_back("-lm");
 
-    TC.AddLinkRuntimeLib(Args, CmdArgs);
+    CmdArgs.push_back(Args.MakeArgString(
+        TC.getCompilerRT(Args, "builtins")));
   }
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
 
   C.addCommand(llvm::make_unique<Command>(JA, *this,
                                           Args.MakeArgString(TC.GetLinkerPath()),
                                           CmdArgs, Inputs));
 }

clang/test/Driver/baremetal.cpp

 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
 // RUN:     -T semihosted.lds \
 // RUN:     -L some/directory/user/asked/for \
 // RUN:     --sysroot=%S/Inputs/baremetal_arm \
 // RUN:   | FileCheck --check-prefix=CHECK-V6M-C %s
 // CHECK-V6M-C: "[[PREFIX_DIR:.*]]{{[/\\]+}}{{[^/^\\]+}}{{[/\\]+}}clang{{.*}}" "-cc1" "-triple" "thumbv6m-none-unknown-eabi"
 // CHECK-V6M-C-SAME: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK-V6M-C-SAME: "-isysroot" "[[SYSROOT:[^"]*]]"
 // CHECK-V6M-C-SAME: "-internal-isystem" "[[SYSROOT]]{{[/\\]+}}include{{[/\\]+}}c++{{[/\\]+}}v1"
 // CHECk-V6M-C-SAME: "-internal-isystem" "[[SYSROOT]]{{[/\\]+}}include"
 // CHECK-V6M-C-SAME: "-x" "c++" "{{.*}}baremetal.cpp"
 // CHECK-V6M-C-NEXT: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"
 // CHECK-V6M-C-SAME: "-L[[RESOURCE_DIR:[^"]+]]{{[/\\]+}}lib{{[/\\]+}}baremetal"
 // CHECK-V6M-C-SAME: "-T" "semihosted.lds" "-Lsome{{[/\\]+}}directory{{[/\\]+}}user{{[/\\]+}}asked{{[/\\]+}}for"
-// CHECK-V6M-C-SAME: "-lc" "-lm" "-lclang_rt.builtins-armv6m.a"
+// CHECK-V6M-C-SAME: "-lc" "-lm"
+// CHECK-V6M-C-SAME: "{{[^"]*}}{{[/\\]+}}lib{{(64)?}}{{[/\\]+}}clang{{[/\\]+}}{{.*}}{{[/\\]+}}lib{{[/\\]+}}libclang_rt.builtins-armv6m.a"
 // CHECK-V6M-C-SAME: "-o" "{{.*}}.o"
 
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
 // RUN:     -nostdlibinc -nobuiltininc \
 // RUN:     --sysroot=%S/Inputs/baremetal_arm \
 // RUN:   | FileCheck --check-prefix=CHECK-V6M-LIBINC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
 // RUN:     -nostdinc \
 // RUN:     --sysroot=%S/Inputs/baremetal_arm \
 // RUN:   | FileCheck --check-prefix=CHECK-V6M-LIBINC %s
 // CHECK-V6M-LIBINC-NOT: "-internal-isystem"
 
 // RUN: %clangxx -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
 // RUN:     --sysroot=%S/Inputs/baremetal_arm \
 // RUN:   | FileCheck --check-prefix=CHECK-V6M-DEFAULTCXX %s
 // CHECK-V6M-DEFAULTCXX: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"
 // CHECK-V6M-DEFAULTCXX-SAME: "-L{{[^"]*}}{{[/\\]+}}lib{{(64)?}}{{[/\\]+}}clang{{[/\\]+}}{{.*}}{{[/\\]+}}lib{{[/\\]+}}baremetal"
 // CHECK-V6M-DEFAULTCXX-SAME: "-lc++" "-lc++abi" "-lunwind"
-// CHECK-V6M-DEFAULTCXX-SAME: "-lc" "-lm" "-lclang_rt.builtins-armv6m.a"
+// CHECK-V6M-DEFAULTCXX-SAME: "-lc" "-lm"
+// CHECK-V6M-DEFAULTCXX-SAME: "{{[^"]*}}{{[/\\]+}}lib{{(64)?}}{{[/\\]+}}clang{{[/\\]+}}{{.*}}{{[/\\]+}}lib{{[/\\]+}}libclang_rt.builtins-armv6m.a"
 // CHECK-V6M-DEFAULTCXX-SAME: "-o" "{{.*}}.o"
 
 // RUN: %clangxx -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
 // RUN:     --sysroot=%S/Inputs/baremetal_arm \
 // RUN:     -stdlib=libc++ \
 // RUN:   | FileCheck --check-prefix=CHECK-V6M-LIBCXX %s
 // CHECK-V6M-LIBCXX-NOT: "-internal-isystem" "{{[^"]+}}{{[/\\]+}}include{{[/\\]+}}c++{{[/\\]+}}{{[^v].*}}"
 // CHECK-V6M-LIBCXX: "-internal-isystem" "{{[^"]+}}{{[/\\]+}}include{{[/\\]+}}c++{{[/\\]+}}v1"
 // CHECK-V6M-LIBCXX: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"
 // CHECK-V6M-LIBCXX-SAME: "-L{{[^"]*}}{{[/\\]+}}lib{{(64)?}}{{[/\\]+}}clang{{[/\\]+}}{{.*}}{{[/\\]+}}lib{{[/\\]+}}baremetal"
 // CHECK-V6M-LIBCXX-SAME: "-lc++" "-lc++abi" "-lunwind"
-// CHECK-V6M-LIBCXX-SAME: "-lc" "-lm" "-lclang_rt.builtins-armv6m.a"
+// CHECK-V6M-LIBCXX-SAME: "-lc" "-lm"
+// CHECK-V6M-LIBCXX-SAME: "{{[^"]*}}{{[/\\]+}}lib{{(64)?}}{{[/\\]+}}clang{{[/\\]+}}{{.*}}{{[/\\]+}}lib{{[/\\]+}}libclang_rt.builtins-armv6m.a"
 // CHECK-V6M-LIBCXX-SAME: "-o" "{{.*}}.o"
 
 // RUN: %clangxx -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
 // RUN:     --sysroot=%S/Inputs/baremetal_arm \
 // RUN:     -stdlib=libstdc++ \
 // RUN:   | FileCheck --check-prefix=CHECK-V6M-LIBSTDCXX %s
 // CHECK-V6M-LIBSTDCXX-NOT: "-internal-isystem" "{{[^"]+}}{{[/\\]+}}include{{[/\\]+}}c++{{[/\\]+}}v1"
 // CHECK-V6M-LIBSTDCXX: "-internal-isystem" "{{[^"]+}}{{[/\\]+}}include{{[/\\]+}}c++{{[/\\]+}}6.0.0"
 // CHECK-V6M-LIBSTDCXX: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"
 // CHECK-V6M-LIBSTDCXX-SAME: "-L{{[^"]*}}{{[/\\]+}}lib{{(64)?}}{{[/\\]+}}clang{{[/\\]+}}{{.*}}{{[/\\]+}}lib{{[/\\]+}}baremetal"
 // CHECK-V6M-LIBSTDCXX-SAME: "-lstdc++" "-lsupc++" "-lunwind"
-// CHECK-V6M-LIBSTDCXX-SAME: "-lc" "-lm" "-lclang_rt.builtins-armv6m.a"
+// CHECK-V6M-LIBSTDCXX-SAME: "-lc" "-lm"
+// CHECK-V6M-LIBSTDCXX-SAME: "{{[^"]*}}{{[/\\]+}}lib{{(64)?}}{{[/\\]+}}clang{{[/\\]+}}{{.*}}{{[/\\]+}}lib{{[/\\]+}}libclang_rt.builtins-armv6m.a"
 // CHECK-V6M-LIBSTDCXX-SAME: "-o" "{{.*}}.o"
 
 // RUN: %clangxx -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
 // RUN:     --sysroot=%S/Inputs/baremetal_arm \
 // RUN:     -nodefaultlibs \
 // RUN:   | FileCheck --check-prefix=CHECK-V6M-NDL %s
 // CHECK-V6M-NDL: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"