[RISCV] Use compiler-rt if no GCC installation detected

[edward-jones]

Summary

If a GCC installation is not detected, then this attempts to use compiler-rt and the compiler-rt crtbegin/crtend implementations as a fallback.

[edward-jones]

Work in progress because this needs tests (and probably clang-format too).

My assumption is that libgcc should be used in preference if it is available. At the moment this either uses libgcc and libgcc's crtbegin/crtend, or the Clang equivalents. Potentially a user might want to mix compiler-rt builtins with libgcc's crt*.o files, but for now that's not possible.

[edward-jones]

Rebased, updated tests from D68391 to check for existence of compiler-rt crtbegin/crtend and runtime library.

[lenary]

Please can you add a test for riscv32 and riscv64 without libgcc?

I also think you want to be smarter about detecting the need/request for libgcc. Look for AddRunTimeLibs in clang/lib/Driver/ToolChains/CommonArgs.cpp - I think that will get you quite far. I think you can override getCompilerRTArgString for your toolchain, and also GetDefaultRuntimeLibType. For the correct compiler-rt stuff, you want ToolChain::getCompilerRT I think. Using all these methods should make these path additions a lot more robust.

[edward-jones]

I've rebased, and also refactored this to use AddRunTimeLibs and GetDefaultRuntimeLibType. The tests have been updated to reflect the changes. Notable changes compared to the last version of the patch:

• AddRunTimeLibs causes -lgcc_s to also be added to the linker command alongside -lgcc. It seems that this is added as part of AddUnwindLibrary in clang/lib/Driver/ToolChains/CommonArgs.cpp. Based on the comments for that function, I would expect to get either -lgcc_s -lgcc or -lgcc -lgcc_eh on the linker command depending on the type of unwinding supported, but this doesn't match the existing behaviour of the RISC-V driver (hence this patch breaks tests), nor does it match the behaviour of RISC-V gcc.
• The search for compiler-rt no longer looks in <prefix>/<triple>/lib for the runtime libraries. It instead looks in the resource directory <prefix>/lib/clang/<version>/lib. This seems to be more correct; out-of-tree compiler-rt builds just need to make sure to set the install prefix to the result of clang -print-resource-dir.

[edward-jones]

In D68407#1709235, @lenary wrote:

Please can you add a test for riscv32 and riscv64 without libgcc?

I'm not sure what you mean here; I believe the existing tests already cover riscv{32,64} without libgcc.

[lenary]

This patch is looking much better, thanks for updating it.

Please may you clarify what RISC-V gcc does for -lgcc, -lgcc_s, -lgcc_eh? Is it different to what gcc does on other targets? Being closer to matching the linker arguments that gcc provides to ld seems like a good idea, IMO.

In D68407#1732619, @edward-jones wrote:

In D68407#1709235, @lenary wrote:

Please can you add a test for riscv32 and riscv64 without libgcc?

I'm not sure what you mean here; I believe the existing tests already cover riscv{32,64} without libgcc.

I'm not sure what I meant there either, sorry. Do disregard that question

[edward-jones]

In D68407#1732685, @lenary wrote:

This patch is looking much better, thanks for updating it.

Please may you clarify what RISC-V gcc does for -lgcc, -lgcc_s, -lgcc_eh? Is it different to what gcc does on other targets? Being closer to matching the linker arguments that gcc provides to ld seems like a good idea, IMO.

The default behaviour on RISC-V GCC is just -lgcc, however for Clang if I call tools::AddRunTimeLibs then by default I get -lgcc --as-needed -lgcc_s --no-as-needed in the link step.

When libgcc is needed tools::AddRunTimeLibs unconditionally calls AddUnwindLibrary, which in turn calls ToolChain::GetUnwindLibType which always returns ToolChain::UNW_Libgcc for libgcc. The code in AddUnwindLibrary will then always add either -lgcc_eh (for a static libgcc), or -lgcc_s (for a shared libgcc) to the command line. I can override this by reimplementing ToolChain::GetUnwindLibType in the target and making it return ToolChain::UNW_None, but I'm not sure whether that's the desired behavior.

[edward-jones]

I've changed this to always return ToolChain::UNW_None from RISCVToolChain::GetUnwindLibType now. As a consequence we get the original behaviour of only -lgcc being added to the link command.

[lenary]

LGTM.

I looked at what g++ and gcc do (my riscv64-unknown-elf toolchain):

• gcc: Passes -lgcc --start-group -lc -lgloss --end-group -lgcc to the linker
• g++: Passes "-lstdc++" -lm -lgcc --start-group -lc -lgloss --end-group -lgcc to the linker

This patch:

• clang passes "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc" to the linker
• clang++ passes "-lstdc++" "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc" to the linker

I think these are all compatible. I'm not sure where the -lm is coming from in the g++ invocation vs the clang++ invocation, but given we have TODOs in this driver code around C++, I don't think that needs to be fixed in this patch.

[MaskRay]

clang/lib/Driver/ToolChains/RISCVToolchain.cpp

68

Ternary operator?

131

Why?

[leonardchan]

Hi. I think this patch is causing some test failures for us:

FAIL: Clang :: Driver/riscv64-toolchain.c (5479 of 16161)
******************** TEST 'Clang :: Driver/riscv64-toolchain.c' FAILED ********************
Script:
--
: 'RUN: at line 3';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -### -no-canonical-prefixes -target riscv64 2>&1 | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck -check-prefix=CC1 /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
: 'RUN: at line 6';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -### -no-canonical-prefixes    -target riscv64-unknown-elf    --gcc-toolchain=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree    --sysroot=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf 2>&1    | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck -check-prefix=C-RV64-BAREMETAL-LP64 /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
: 'RUN: at line 22';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -### -no-canonical-prefixes    -target riscv64-unknown-elf    --sysroot=    --gcc-toolchain=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree 2>&1    | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck -check-prefix=C-RV64-BAREMETAL-NOSYSROOT-LP64 /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
: 'RUN: at line 37';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang --driver-mode=g++ /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -### -no-canonical-prefixes    -target riscv64-unknown-elf -stdlib=libstdc++    --gcc-toolchain=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree    --sysroot=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf 2>&1    | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck -check-prefix=CXX-RV64-BAREMETAL-LP64 /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
: 'RUN: at line 54';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang --driver-mode=g++ /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -### -no-canonical-prefixes    -target riscv64-unknown-elf -stdlib=libstdc++    --sysroot=    --gcc-toolchain=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree 2>&1    | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck -check-prefix=CXX-RV64-BAREMETAL-NOSYSROOT-LP64 /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
: 'RUN: at line 70';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -### -no-canonical-prefixes -fuse-ld=ld    -target riscv64-unknown-linux-gnu -mabi=lp64    --gcc-toolchain=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/multilib_riscv_linux_sdk    --sysroot=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1    | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck -check-prefix=C-RV64-LINUX-MULTI-LP64 /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
: 'RUN: at line 86';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -### -no-canonical-prefixes -fuse-ld=ld    -target riscv64-unknown-linux-gnu -march=rv64imafd    --gcc-toolchain=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/multilib_riscv_linux_sdk    --sysroot=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1    | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck -check-prefix=C-RV64-LINUX-MULTI-LP64D /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
: 'RUN: at line 102';   /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/clang -target riscv64 /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c -emit-llvm -S -o - | /b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/bin/FileCheck /b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c
--
Exit Code: 1

Command Output (stderr):
--
/b/s/w/ir/k/llvm-project/clang/test/Driver/riscv64-toolchain.c:16:27: error: C-RV64-BAREMETAL-LP64: expected string not found in input
// C-RV64-BAREMETAL-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
                          ^
<stdin>:6:349: note: scanning from here
 "/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../../../bin/riscv64-unknown-elf-ld" "--sysroot=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf" "/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib/crt0.o" "/b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/lib/clang/10.0.0/lib/clang_rt.crtbegin-riscv64.o" "-L/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib" "-L/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1" "/b/s/w/ir/tmp/t/riscv64-toolchain-ae7410.o" "--start-group" "-lc" "-lgloss" "--end-group" "/b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/lib/clang/10.0.0/lib/libclang_rt.builtins-riscv64.a" "/b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/lib/clang/10.0.0/lib/clang_rt.crtend-riscv64.o" "-o" "a.out"
                                                                                                                                                                                                                                                                                                                                                            ^
<stdin>:6:591: note: possible intended match here
 "/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../../../bin/riscv64-unknown-elf-ld" "--sysroot=/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf" "/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib/crt0.o" "/b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/lib/clang/10.0.0/lib/clang_rt.crtbegin-riscv64.o" "-L/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib" "-L/b/s/w/ir/k/llvm-project/clang/test/Driver/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1" "/b/s/w/ir/tmp/t/riscv64-toolchain-ae7410.o" "--start-group" "-lc" "-lgloss" "--end-group" "/b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/lib/clang/10.0.0/lib/libclang_rt.builtins-riscv64.a" "/b/s/w/ir/k/recipe_cleanup/clangeX2xRw/llvm_build_dir/lib/clang/10.0.0/lib/clang_rt.crtend-riscv64.o" "-o" "a.out"
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
... and one more

Could you take a look? Thanks.

Link to error: https://ci.chromium.org/p/fuchsia/builders/ci/clang-linux-x64/b8896884112835419104

[rsmith]

In D68407#1744486, @leonardchan wrote:

Hi. I think this patch is causing some test failures for us:

This is breaking us too, in the same way. The "problem" is that this makes the riscv64 target use the compiler-rt crtbegin / crtend files instead of the libgcc ones when configured with -DCLANG_DEFAULT_RTLIB=compiler-rt. That's probably the right behavior, but someone should check, and additional tests need to be updated to match. (It's not obvious how to even test this change in the presence of CLANG_DEFAULT_RTLIB...)

The following tests fail in the -DCLANG_DEFAULT_RTLIB=compiler-rt build configuration:

• test/Driver/riscv32-toolchain.c
• test/Driver/riscv32-toolchain-extra.c
• test/Driver/riscv64-toolchain.c
• test/Driver/riscv64-toolchain-extra.c

Reverted in aeaddf9 to unbreak things for now.

[edward-jones]

Okay. I'll see if I can find a way to test this when CLANG_DEFAULT_RTLIB is set, and then I'll resubmit

[edward-jones]

It seems that the option --rtlib=platform exists to force the driver to ignore the -DCLANG_DEFAULT_RTLIB for testing purposes, so I've added this option to the tests that were broken.

These tests now seem to pass regardless of whether CLANG_DEFAULT_RTLIB is set to compiler-rt or libgcc.

I'm leaving this WIP as I think it will be prudent to add some tests for --rtlib=compiler and --rtlib=libgcc.

[edward-jones]

If I set -DCLANG_DEFAULT_RTLIB=compiler-rt I see the following failure in clang/test/Driver/cross-linux.c:

/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/cross-linux.c:62:26: error: CHECK-MULTI32-X86-64: expected string not found in input
// CHECK-MULTI32-X86-64: "crti.o" "[[gcc_install:.*/Inputs/multilib_32bit_linux_tree/usr/lib/gcc/i386-unknown-linux/4.6.0]]/64{{/|\\\\}}crtbegin.o"
                         ^
<stdin>:7:327: note: scanning from here
 "/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/multilib_32bit_linux_tree/usr/lib/gcc/i386-unknown-linux/4.6.0/../../../../i386-unknown-linux/bin/ld" "--sysroot=/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/basic_linux_tree" "-z" "relro" "--hash-style=gnu" "--eh-frame-hdr" "-m" "elf_x86_64" "-dynamic-linker" "/lib64/ld-linux-x86-64.so.2" "-o" "/home/ed/work/proj/riscv-testing/build/llvm/tools/clang/test/Driver/Output/cross-linux.c.tmp" "crt1.o" "crti.o" "/home/ed/work/proj/riscv-testing/build/llvm/lib/clang/10.0.0/lib/linux/clang_rt.crtbegin-x86_64.o" "-L/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/multilib_32bit_linux_tree/usr/lib/gcc/i386-unknown-linux/4.6.0/64" "-L/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/multilib_32bit_linux_tree/usr/lib/gcc/i386-unknown-linux/4.6.0/../../../../i386-unknown-linux/lib/../lib64" "-L/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/multilib_32bit_linux_tree/usr/lib/gcc/i386-unknown-linux/4.6.0" "-L/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/multilib_32bit_linux_tree/usr/lib/gcc/i386-unknown-linux/4.6.0/../../../../i386-unknown-linux/lib" "-L/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/basic_linux_tree/lib" "-L/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/Inputs/basic_linux_tree/usr/lib" "/tmp/cross-linux-bb2220.o" "/home/ed/work/proj/riscv-testing/build/llvm/lib/clang/10.0.0/lib/linux/libclang_rt.builtins-x86_64.a" "--as-needed" "-lgcc_s" "--no-as-needed" "-lc" "/home/ed/work/proj/riscv-testing/build/llvm/lib/clang/10.0.0/lib/linux/libclang_rt.builtins-x86_64.a" "--as-needed" "-lgcc_s" "--no-as-needed" "/home/ed/work/proj/riscv-testing/build/llvm/lib/clang/10.0.0/lib/linux/clang_rt.crtend-x86_64.o" "crtn.o"
                                                                                                                                                                                                                                                                                                                                      ^

And if I set -DCLANG_DEFAULT_RTLIB=libgcc then I see the following failure in clang/test/Driver/wasm-toolchain.cpp:

/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/wasm-toolchain.cpp:20:10: error: LINK: expected string not found in input
// LINK: wasm-ld{{.*}}" "-L/foo/lib" "crt1.o" "[[temp]]" "-lc++" "-lc++abi" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"

<stdin>:6:1018: note: scanning from here
 "/home/ed/work/proj/riscv-testing/build/llvm/bin/clang" "-cc1" "-triple" "wasm32-unknown-unknown" "-emit-obj" "-mrelax-all" "-disable-free" "-main-file-name" "wasm-toolchain.cpp" "-mrelocation-model" "static" "-mthread-model" "posix" "-mframe-pointer=none" "-fno-rounding-math" "-masm-verbose" "-mconstructor-aliases" "-fuse-init-array" "-target-cpu" "generic" "-fvisibility" "hidden" "-dwarf-column-info" "-debugger-tuning=gdb" "-resource-dir" "/home/ed/work/proj/riscv-testing/build/llvm/lib/clang/10.0.0" "-isysroot" "/foo" "-internal-isystem" "/foo/include/c++/v1" "-internal-isystem" "/home/ed/work/proj/riscv-testing/build/llvm/lib/clang/10.0.0/include" "-internal-isystem" "/foo/include" "-fdeprecated-macro" "-fdebug-compilation-dir" "/home/ed/work/proj/riscv-testing/build/llvm/tools/clang/test/Driver" "-ferror-limit" "19" "-fmessage-length" "0" "-fgnuc-version=4.2.1" "-fobjc-runtime=gnustep" "-fcxx-exceptions" "-fexceptions" "-fno-common" "-fdiagnostics-show-option" "-o" "/tmp/wasm-toolchain-718d0c.o" "-x" "c++" "/home/ed/work/proj/riscv-testing/llvm/clang/test/Driver/wasm-toolchain.cpp"
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         ^

I don't see how these tests could be affected by this patch, so I'm wondering whether these tests have always been broken?

[edward-jones]

Added tests that a user can specify a specific runtime library through --rtlib. Also rebased on master, and added a comment explaining the use of --rtlib=platform in the tests.

[lenary]

Nice, LGTM! Thanks for fixing this in the presence of CLANG_DEFAULT_RTLIB.

clang/lib/Driver/ToolChains/RISCVToolchain.h

 public:
   RISCVToolChain(const Driver &D, const llvm::Triple &Triple,
                  const llvm::opt::ArgList &Args);
 
   bool IsIntegratedAssemblerDefault() const override { return true; }
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args,
                              Action::OffloadKind) const override;
+  RuntimeLibType GetDefaultRuntimeLibType() const override;
+  UnwindLibType
+  GetUnwindLibType(const llvm::opt::ArgList &Args) const override;
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
   void
   addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const override;
 
 protected:

clang/lib/Driver/ToolChains/RISCVToolchain.cpp

RISCVToolChain::RISCVToolChain(const Driver &D, const llvm::Triple &Triple,
   }
   getFilePaths().push_back(computeSysRoot() + "/lib");
 }
 
 Tool *RISCVToolChain::buildLinker() const {
   return new tools::RISCV::Linker(*this);
 }
 
+ToolChain::RuntimeLibType RISCVToolChain::GetDefaultRuntimeLibType() const {
+  return GCCInstallation.isValid() ?
+    ToolChain::RLT_Libgcc : ToolChain::RLT_CompilerRT;
+}
+
+ToolChain::UnwindLibType
+RISCVToolChain::GetUnwindLibType(const llvm::opt::ArgList &Args) const {
+  return ToolChain::UNW_None;
+}
+
 void RISCVToolChain::addClangTargetOptions(
     const llvm::opt::ArgList &DriverArgs,
     llvm::opt::ArgStringList &CC1Args,
     Action::OffloadKind) const {
   CC1Args.push_back("-nostdsysteminc");
   CC1Args.push_back("-fuse-init-array");
 }
 
std::string RISCVToolChain::computeSysRoot() const {
   return SysRootDir.str();
 }
 
 void RISCV::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                  const InputInfo &Output,
                                  const InputInfoList &Inputs,
                                  const ArgList &Args,
                                  const char *LinkingOutput) const {
   const ToolChain &ToolChain = getToolChain();
   const Driver &D = ToolChain.getDriver();
   ArgStringList CmdArgs;
 
   if (!D.SysRoot.empty())
     CmdArgs.push_back(Args.MakeArgString("--sysroot=" + D.SysRoot));
 
   bool IsRV64 = ToolChain.getArch() == llvm::Triple::riscv64;
   CmdArgs.push_back("-m");
   if (IsRV64) {
     CmdArgs.push_back("elf64lriscv");
   } else {
     CmdArgs.push_back("elf32lriscv");
   }
 
   std::string Linker = getToolChain().GetProgramPath(getShortName());
 
   bool WantCRTs =
       !Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles);
 
+  const char *crtbegin, *crtend;
+  auto RuntimeLib = ToolChain.GetRuntimeLibType(Args);
+  if (RuntimeLib == ToolChain::RLT_Libgcc) {
+    crtbegin = "crtbegin.o";
+    crtend = "crtend.o";
+  } else {
+    assert (RuntimeLib == ToolChain::RLT_CompilerRT);
+    crtbegin = ToolChain.getCompilerRTArgString(Args, "crtbegin",
+                                                ToolChain::FT_Object);
+    crtend = ToolChain.getCompilerRTArgString(Args, "crtend",
+                                              ToolChain::FT_Object);
+  }
+
   if (WantCRTs) {
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crt0.o")));
-    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtbegin.o")));
+    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtbegin)));
   }
 
   Args.AddAllArgs(CmdArgs, options::OPT_L);
   ToolChain.AddFilePathLibArgs(Args, CmdArgs);
   Args.AddAllArgs(CmdArgs,
                   {options::OPT_T_Group, options::OPT_e, options::OPT_s,
                    options::OPT_t, options::OPT_Z_Flag, options::OPT_r});
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   // TODO: add C++ includes and libs if compiling C++.
 
   if (!Args.hasArg(options::OPT_nostdlib) &&
       !Args.hasArg(options::OPT_nodefaultlibs)) {
     if (ToolChain.ShouldLinkCXXStdlib(Args))
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
     CmdArgs.push_back("--start-group");
     CmdArgs.push_back("-lc");
     CmdArgs.push_back("-lgloss");
     CmdArgs.push_back("--end-group");
-    CmdArgs.push_back("-lgcc");
+    AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
   }
 
   if (WantCRTs)
-    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtend.o")));
+    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtend)));
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
   C.addCommand(std::make_unique<Command>(JA, *this, Args.MakeArgString(Linker),
                                           CmdArgs, Inputs));
 }
 // RISCV tools end.

clang/test/Driver/riscv32-toolchain-extra.c

 // RUN: mkdir -p %T/testroot-riscv32-baremetal-nogcc/bin
 // RUN: [ ! -s %T/testroot-riscv32-baremetal-nogcc/bin/clang ] || rm %T/testroot-riscv32-baremetal-nogcc/bin/clang
 // RUN: [ ! -s %T/testroot-riscv32-baremetal-nogcc/bin/riscv32-unknown-elf-ld ] || rm %T/testroot-riscv32-baremetal-nogcc/bin/riscv32-unknown-elf-ld
 // RUN: [ ! -s %T/testroot-riscv32-baremetal-nogcc/riscv32-unknown-elf ] || rm %T/testroot-riscv32-baremetal-nogcc/riscv32-unknown-elf
 // RUN: ln -s %clang %T/testroot-riscv32-baremetal-nogcc/bin/clang
 // RUN: ln -s %S/Inputs/basic_riscv32_nogcc_tree/bin/riscv32-unknown-elf-ld %T/testroot-riscv32-baremetal-nogcc/bin/riscv32-unknown-elf-ld
 // RUN: ln -s %S/Inputs/basic_riscv32_nogcc_tree/riscv32-unknown-elf %T/testroot-riscv32-baremetal-nogcc/riscv32-unknown-elf
 // RUN: %T/testroot-riscv32-baremetal-nogcc/bin/clang %s -### -no-canonical-prefixes \
-// RUN:    -target riscv32-unknown-elf 2>&1 \
+// RUN:    -target riscv32-unknown-elf --rtlib=platform 2>&1 \
 // RUN:    | FileCheck -check-prefix=C-RV32-BAREMETAL-ILP32-NOGCC %s
 
-// C-RV32-BAREMETAL-ILP32-NOGCC: InstalledDir: [[DRIVERDIR:.*]]
 // C-RV32-BAREMETAL-ILP32-NOGCC: "-fuse-init-array"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "-internal-isystem" "[[DRIVERDIR]]/../riscv32-unknown-elf/include"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/riscv32-unknown-elf-ld"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/../riscv32-unknown-elf/lib/crt0.o"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/../riscv32-unknown-elf/lib/crtbegin.o"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "-L[[DRIVERDIR]]/../riscv32-unknown-elf/lib"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/../riscv32-unknown-elf/lib/crtend.o"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/../riscv32-unknown-elf/include"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/riscv32-unknown-elf-ld"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/../riscv32-unknown-elf/lib/crt0.o"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtbegin-riscv32.o"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/../riscv32-unknown-elf/lib"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/libclang_rt.builtins-riscv32.a"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtend-riscv32.o"

clang/test/Driver/riscv32-toolchain.c

 // A basic clang -cc1 command-line, and simple environment check.
 
 // RUN: %clang %s -### -no-canonical-prefixes -target riscv32 2>&1 | FileCheck -check-prefix=CC1 %s
 // CC1: clang{{.*}} "-cc1" "-triple" "riscv32"
 
+// In the below tests, --rtlib=platform is used so that the driver ignores
+// the configure-time CLANG_DEFAULT_RTLIB option when choosing the runtime lib
+
 // RUN: %clang %s -### -no-canonical-prefixes \
-// RUN:   -target riscv32-unknown-elf \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv32_tree \
 // RUN:   --sysroot=%S/Inputs/basic_riscv32_tree/riscv32-unknown-elf 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32-BAREMETAL-ILP32 %s
 
 // C-RV32-BAREMETAL-ILP32: "-fuse-init-array"
 // C-RV32-BAREMETAL-ILP32: "{{.*}}Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv32-unknown-elf-ld"
 // C-RV32-BAREMETAL-ILP32: "--sysroot={{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf"
 // C-RV32-BAREMETAL-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf/lib{{/|\\\\}}crt0.o"
 // C-RV32-BAREMETAL-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // C-RV32-BAREMETAL-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1"
 // C-RV32-BAREMETAL-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf/lib"
 // C-RV32-BAREMETAL-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV32-BAREMETAL-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes \
-// RUN:   -target riscv32-unknown-elf \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform \
 // RUN:   --sysroot= \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv32_tree 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32-BAREMETAL-NOSYSROOT-ILP32 %s
 
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "-fuse-init-array"
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv32-unknown-elf-ld"
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv32-unknown-elf/lib{{/|\\\\}}crt0.o"
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1"
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv32-unknown-elf{{/|\\\\}}lib"
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clangxx %s -### -no-canonical-prefixes \
-// RUN:   -target riscv32-unknown-elf -stdlib=libstdc++ \
+// RUN:   -target riscv32-unknown-elf -stdlib=libstdc++ --rtlib=platform \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv32_tree \
 // RUN:   --sysroot=%S/Inputs/basic_riscv32_tree/riscv32-unknown-elf 2>&1 \
 // RUN:   | FileCheck -check-prefix=CXX-RV32-BAREMETAL-ILP32 %s
 
 // CXX-RV32-BAREMETAL-ILP32: "-fuse-init-array"
 // CXX-RV32-BAREMETAL-ILP32: "-internal-isystem" "{{.*}}Inputs/basic_riscv32_tree/riscv32-unknown-elf/include/c++{{/|\\\\}}8.0.1"
 // CXX-RV32-BAREMETAL-ILP32: "{{.*}}Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv32-unknown-elf-ld"
 // CXX-RV32-BAREMETAL-ILP32: "--sysroot={{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf"
 // CXX-RV32-BAREMETAL-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf/lib{{/|\\\\}}crt0.o"
 // CXX-RV32-BAREMETAL-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // CXX-RV32-BAREMETAL-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1"
 // CXX-RV32-BAREMETAL-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf/lib"
 // CXX-RV32-BAREMETAL-ILP32: "-lstdc++" "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // CXX-RV32-BAREMETAL-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clangxx %s -### -no-canonical-prefixes \
-// RUN:   -target riscv32-unknown-elf -stdlib=libstdc++ \
+// RUN:   -target riscv32-unknown-elf -stdlib=libstdc++ --rtlib=platform \
 // RUN:   --sysroot= \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv32_tree 2>&1 \
 // RUN:   | FileCheck -check-prefix=CXX-RV32-BAREMETAL-NOSYSROOT-ILP32 %s
 
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "-fuse-init-array"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "-internal-isystem" "{{.*}}Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv32-unknown-elf/include/c++{{/|\\\\}}8.0.1"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv32-unknown-elf-ld"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv32-unknown-elf/lib{{/|\\\\}}crt0.o"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "-L{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv32-unknown-elf/lib"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "-lstdc++" "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // CXX-RV32-BAREMETAL-NOSYSROOT-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv32-unknown-linux-gnu -mabi=ilp32 \
+// RUN:   -target riscv32-unknown-linux-gnu --rtlib=platform -mabi=ilp32 \
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
 // RUN:   --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32-LINUX-MULTI-ILP32 %s
 
 // C-RV32-LINUX-MULTI-ILP32: "-fuse-init-array"
 // C-RV32-LINUX-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-linux-gnu/bin{{/|\\\\}}ld"
 // C-RV32-LINUX-MULTI-ILP32: "--sysroot={{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot"
 // C-RV32-LINUX-MULTI-ILP32: "-m" "elf32lriscv"
 // C-RV32-LINUX-MULTI-ILP32: "-dynamic-linker" "/lib/ld-linux-riscv32-ilp32.so.1"
 // C-RV32-LINUX-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib32/ilp32{{/|\\\\}}crtbegin.o"
 // C-RV32-LINUX-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib32/ilp32"
 // C-RV32-LINUX-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/lib32/ilp32"
 // C-RV32-LINUX-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/usr/lib32/ilp32"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv32-unknown-linux-gnu -march=rv32imafd \
+// RUN:   -target riscv32-unknown-linux-gnu --rtlib=platform -march=rv32imafd \
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
 // RUN:   --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32-LINUX-MULTI-ILP32D %s
 
 // C-RV32-LINUX-MULTI-ILP32D: "-fuse-init-array"
 // C-RV32-LINUX-MULTI-ILP32D: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-linux-gnu/bin{{/|\\\\}}ld"
 // C-RV32-LINUX-MULTI-ILP32D: "--sysroot={{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot"
 // C-RV32-LINUX-MULTI-ILP32D: "-m" "elf32lriscv"
 // C-RV32-LINUX-MULTI-ILP32D: "-dynamic-linker" "/lib/ld-linux-riscv32-ilp32d.so.1"
 // C-RV32-LINUX-MULTI-ILP32D: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib32/ilp32d{{/|\\\\}}crtbegin.o"
 // C-RV32-LINUX-MULTI-ILP32D: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib32/ilp32d"
 // C-RV32-LINUX-MULTI-ILP32D: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/lib32/ilp32d"
 // C-RV32-LINUX-MULTI-ILP32D: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/usr/lib32/ilp32d"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv32-unknown-elf --sysroot= \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform --sysroot= \
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_elf_sdk 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32I-BAREMETAL-MULTI-ILP32 %s
 
 // C-RV32I-BAREMETAL-MULTI-ILP32: "-fuse-init-array"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/bin{{/|\\\\}}ld"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "-m" "elf32lriscv"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32imac/ilp32{{/|\\\\}}crt0.o"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32imac/ilp32{{/|\\\\}}crtbegin.o"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV32I-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32imac/ilp32{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv32-unknown-elf --sysroot= -march=rv32im -mabi=ilp32\
+// RUN:   -target riscv32-unknown-elf --rtlib=platform --sysroot= \
+// RUN:   -march=rv32im -mabi=ilp32\
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_elf_sdk 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32IM-BAREMETAL-MULTI-ILP32 %s
 
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "-fuse-init-array"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/bin{{/|\\\\}}ld"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "-m" "elf32lriscv"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32im/ilp32{{/|\\\\}}crt0.o"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32im/ilp32{{/|\\\\}}crtbegin.o"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV32IM-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32im/ilp32{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv32-unknown-elf --sysroot= -march=rv32iac -mabi=ilp32\
+// RUN:   -target riscv32-unknown-elf --rtlib=platform --sysroot= \
+// RUN:   -march=rv32iac -mabi=ilp32\
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_elf_sdk 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32IAC-BAREMETAL-MULTI-ILP32 %s
 
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "-fuse-init-array"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/bin{{/|\\\\}}ld"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "-m" "elf32lriscv"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32iac/ilp32{{/|\\\\}}crt0.o"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32iac/ilp32{{/|\\\\}}crtbegin.o"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV32IAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32iac/ilp32{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv32-unknown-elf --sysroot= -march=rv32imac -mabi=ilp32\
+// RUN:   -target riscv32-unknown-elf --rtlib=platform --sysroot= \
+// RUN:   -march=rv32imac -mabi=ilp32\
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_elf_sdk 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32IMAC-BAREMETAL-MULTI-ILP32 %s
 
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "-fuse-init-array"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/bin{{/|\\\\}}ld"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "-m" "elf32lriscv"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32imac/ilp32{{/|\\\\}}crt0.o"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32imac/ilp32{{/|\\\\}}crtbegin.o"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV32IMAC-BAREMETAL-MULTI-ILP32: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32imac/ilp32{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv32-unknown-elf --sysroot= -march=rv32imafc -mabi=ilp32f \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform --sysroot= \
+// RUN:   -march=rv32imafc -mabi=ilp32f \
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_elf_sdk 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV32IMAFC-BAREMETAL-MULTI-ILP32F %s
 
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "-fuse-init-array"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/bin{{/|\\\\}}ld"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "-m" "elf32lriscv"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32imafc/ilp32f{{/|\\\\}}crt0.o"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32imafc/ilp32f{{/|\\\\}}crtbegin.o"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV32IMAFC-BAREMETAL-MULTI-ILP32F: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv32imafc/ilp32f{{/|\\\\}}crtend.o"
 
+// Check that --rtlib can be used to override the used runtime library
+// RUN: %clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv32-unknown-elf --rtlib=libgcc 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV32-RTLIB-LIBGCC-ILP32 %s
+// C-RV32-RTLIB-LIBGCC-ILP32: "{{.*}}crt0.o"
+// C-RV32-RTLIB-LIBGCC-ILP32: "{{.*}}crtbegin.o"
+// C-RV32-RTLIB-LIBGCC-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
+// C-RV32-RTLIB-LIBGCC-ILP32: "{{.*}}crtend.o"
+
+// RUN: %clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv32-unknown-elf --rtlib=compiler-rt 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV32-RTLIB-COMPILERRT-ILP32 %s
+// C-RV32-RTLIB-COMPILERRT-ILP32: "{{.*}}crt0.o"
+// C-RV32-RTLIB-COMPILERRT-ILP32: "{{.*}}clang_rt.crtbegin-riscv32.o"
+// C-RV32-RTLIB-COMPILERRT-ILP32: "--start-group" "-lc" "-lgloss" "--end-group" "{{.*}}libclang_rt.builtins-riscv32.a"
+// C-RV32-RTLIB-COMPILERRT-ILP32: "{{.*}}clang_rt.crtend-riscv32.o"
+
 // RUN: %clang -target riscv32 %s -emit-llvm -S -o - | FileCheck %s
 
 typedef __builtin_va_list va_list;
 typedef __SIZE_TYPE__ size_t;
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
 typedef __WCHAR_TYPE__ wchar_t;
 typedef __WINT_TYPE__ wint_t;
 

clang/test/Driver/riscv64-toolchain-extra.c

 // RUN: mkdir -p %T/testroot-riscv64-baremetal-nogcc/bin
 // RUN: [ ! -s %T/testroot-riscv64-baremetal-nogcc/bin/clang ] || rm %T/testroot-riscv64-baremetal-nogcc/bin/clang
 // RUN: [ ! -s %T/testroot-riscv64-baremetal-nogcc/bin/riscv64-unknown-elf-ld ] || rm %T/testroot-riscv64-baremetal-nogcc/bin/riscv64-unknown-elf-ld
 // RUN: [ ! -s %T/testroot-riscv64-baremetal-nogcc/riscv64-unknown-elf ] || rm %T/testroot-riscv64-baremetal-nogcc/riscv64-unknown-elf
 // RUN: ln -s %clang %T/testroot-riscv64-baremetal-nogcc/bin/clang
 // RUN: ln -s %S/Inputs/basic_riscv64_nogcc_tree/bin/riscv64-unknown-elf-ld %T/testroot-riscv64-baremetal-nogcc/bin/riscv64-unknown-elf-ld
 // RUN: ln -s %S/Inputs/basic_riscv64_nogcc_tree/riscv64-unknown-elf %T/testroot-riscv64-baremetal-nogcc/riscv64-unknown-elf
 // RUN: %T/testroot-riscv64-baremetal-nogcc/bin/clang %s -### -no-canonical-prefixes \
-// RUN:    -target riscv64-unknown-elf 2>&1 \
+// RUN:    -target riscv64-unknown-elf --rtlib=platform 2>&1 \
 // RUN:    | FileCheck -check-prefix=C-RV64-BAREMETAL-LP64-NOGCC %s
 
-// C-RV64-BAREMETAL-LP64-NOGCC: InstalledDir: [[DRIVERDIR:.*]]
 // C-RV64-BAREMETAL-LP64-NOGCC: "-fuse-init-array"
-// C-RV64-BAREMETAL-LP64-NOGCC: "-internal-isystem" "[[DRIVERDIR]]/../riscv64-unknown-elf/include"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/riscv64-unknown-elf-ld"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/../riscv64-unknown-elf/lib/crt0.o"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/../riscv64-unknown-elf/lib/crtbegin.o"
-// C-RV64-BAREMETAL-LP64-NOGCC: "-L[[DRIVERDIR]]/../riscv64-unknown-elf/lib"
-// C-RV64-BAREMETAL-LP64-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/../riscv64-unknown-elf/lib/crtend.o"
+// C-RV64-BAREMETAL-LP64-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/riscv64-unknown-elf-ld"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/../riscv64-unknown-elf/lib/crt0.o"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtbegin-riscv64.o"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV64-BAREMETAL-LP64-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/libclang_rt.builtins-riscv64.a"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtend-riscv64.o"

clang/test/Driver/riscv64-toolchain.c

 // A basic clang -cc1 command-line, and simple environment check.
 
 // RUN: %clang %s -### -no-canonical-prefixes -target riscv64 2>&1 | FileCheck -check-prefix=CC1 %s
 // CC1: clang{{.*}} "-cc1" "-triple" "riscv64"
 
+// In the below tests, --rtlib=platform is used so that the driver ignores
+// the configure-time CLANG_DEFAULT_RTLIB option when choosing the runtime lib
+
 // RUN: %clang %s -### -no-canonical-prefixes \
-// RUN:   -target riscv64-unknown-elf \
+// RUN:   -target riscv64-unknown-elf --rtlib=platform \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv64_tree \
 // RUN:   --sysroot=%S/Inputs/basic_riscv64_tree/riscv64-unknown-elf 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV64-BAREMETAL-LP64 %s
 
 // C-RV64-BAREMETAL-LP64: "-fuse-init-array"
 // C-RV64-BAREMETAL-LP64: "{{.*}}Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv64-unknown-elf-ld"
 // C-RV64-BAREMETAL-LP64: "--sysroot={{.*}}/Inputs/basic_riscv64_tree/riscv64-unknown-elf"
 // C-RV64-BAREMETAL-LP64: "{{.*}}/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib{{/|\\\\}}crt0.o"
 // C-RV64-BAREMETAL-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // C-RV64-BAREMETAL-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1"
 // C-RV64-BAREMETAL-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib"
 // C-RV64-BAREMETAL-LP64: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV64-BAREMETAL-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes \
-// RUN:   -target riscv64-unknown-elf \
+// RUN:   -target riscv64-unknown-elf --rtlib=platform \
 // RUN:   --sysroot= \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv64_tree 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV64-BAREMETAL-NOSYSROOT-LP64 %s
 
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "-fuse-init-array"
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv64-unknown-elf-ld"
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib{{/|\\\\}}crt0.o"
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1"
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf{{/|\\\\}}lib"
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clangxx %s -### -no-canonical-prefixes \
-// RUN:   -target riscv64-unknown-elf -stdlib=libstdc++ \
+// RUN:   -target riscv64-unknown-elf -stdlib=libstdc++ --rtlib=platform \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv64_tree \
 // RUN:   --sysroot=%S/Inputs/basic_riscv64_tree/riscv64-unknown-elf 2>&1 \
 // RUN:   | FileCheck -check-prefix=CXX-RV64-BAREMETAL-LP64 %s
 
 // CXX-RV64-BAREMETAL-LP64: "-fuse-init-array"
 // CXX-RV64-BAREMETAL-LP64: "-internal-isystem" "{{.*}}Inputs/basic_riscv64_tree/riscv64-unknown-elf/include/c++{{/|\\\\}}8.0.1"
 // CXX-RV64-BAREMETAL-LP64: "{{.*}}Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv64-unknown-elf-ld"
 // CXX-RV64-BAREMETAL-LP64: "--sysroot={{.*}}/Inputs/basic_riscv64_tree/riscv64-unknown-elf"
 // CXX-RV64-BAREMETAL-LP64: "{{.*}}/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib{{/|\\\\}}crt0.o"
 // CXX-RV64-BAREMETAL-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // CXX-RV64-BAREMETAL-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1"
 // CXX-RV64-BAREMETAL-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/riscv64-unknown-elf/lib"
 // CXX-RV64-BAREMETAL-LP64: "-lstdc++" "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // CXX-RV64-BAREMETAL-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clangxx %s -### -no-canonical-prefixes \
-// RUN:   -target riscv64-unknown-elf -stdlib=libstdc++ \
+// RUN:   -target riscv64-unknown-elf -stdlib=libstdc++ --rtlib=platform \
 // RUN:   --sysroot= \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_riscv64_tree 2>&1 \
 // RUN:   | FileCheck -check-prefix=CXX-RV64-BAREMETAL-NOSYSROOT-LP64 %s
 
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "-fuse-init-array"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "-internal-isystem" "{{.*}}Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/include/c++{{/|\\\\}}8.0.1"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}bin{{/|\\\\}}riscv64-unknown-elf-ld"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib{{/|\\\\}}crt0.o"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtbegin.o"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "-L{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "-lstdc++" "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // CXX-RV64-BAREMETAL-NOSYSROOT-LP64: "{{.*}}/Inputs/basic_riscv64_tree/lib/gcc/riscv64-unknown-elf/8.0.1{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv64-unknown-linux-gnu -mabi=lp64 \
+// RUN:   -target riscv64-unknown-linux-gnu --rtlib=platform -mabi=lp64 \
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
 // RUN:   --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV64-LINUX-MULTI-LP64 %s
 
 // C-RV64-LINUX-MULTI-LP64: "-fuse-init-array"
 // C-RV64-LINUX-MULTI-LP64: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-linux-gnu/bin{{/|\\\\}}ld"
 // C-RV64-LINUX-MULTI-LP64: "--sysroot={{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot"
 // C-RV64-LINUX-MULTI-LP64: "-m" "elf64lriscv"
 // C-RV64-LINUX-MULTI-LP64: "-dynamic-linker" "/lib/ld-linux-riscv64-lp64.so.1"
 // C-RV64-LINUX-MULTI-LP64: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib64/lp64{{/|\\\\}}crtbegin.o"
 // C-RV64-LINUX-MULTI-LP64: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib64/lp64"
 // C-RV64-LINUX-MULTI-LP64: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/lib64/lp64"
 // C-RV64-LINUX-MULTI-LP64: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/usr/lib64/lp64"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv64-unknown-linux-gnu -march=rv64imafd \
+// RUN:   -target riscv64-unknown-linux-gnu --rtlib=platform -march=rv64imafd \
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
 // RUN:   --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV64-LINUX-MULTI-LP64D %s
 
 // C-RV64-LINUX-MULTI-LP64D: "-fuse-init-array"
 // C-RV64-LINUX-MULTI-LP64D: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-linux-gnu/bin{{/|\\\\}}ld"
 // C-RV64-LINUX-MULTI-LP64D: "--sysroot={{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot"
 // C-RV64-LINUX-MULTI-LP64D: "-m" "elf64lriscv"
 // C-RV64-LINUX-MULTI-LP64D: "-dynamic-linker" "/lib/ld-linux-riscv64-lp64d.so.1"
 // C-RV64-LINUX-MULTI-LP64D: "{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib64/lp64d{{/|\\\\}}crtbegin.o"
 // C-RV64-LINUX-MULTI-LP64D: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/lib/gcc/riscv64-unknown-linux-gnu/7.2.0/lib64/lp64d"
 // C-RV64-LINUX-MULTI-LP64D: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/lib64/lp64d"
 // C-RV64-LINUX-MULTI-LP64D: "-L{{.*}}/Inputs/multilib_riscv_linux_sdk/sysroot/usr/lib64/lp64d"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv64-unknown-elf --sysroot= -march=rv64imac -mabi=lp64\
+// RUN:   -target riscv64-unknown-elf --rtlib=platform --sysroot= \
+// RUN:   -march=rv64imac -mabi=lp64\
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_elf_sdk 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV64IMAC-BAREMETAL-MULTI-LP64 %s
 
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "-fuse-init-array"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/bin{{/|\\\\}}ld"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "-m" "elf64lriscv"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv64imac/lp64{{/|\\\\}}crt0.o"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv64imac/lp64{{/|\\\\}}crtbegin.o"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV64IMAC-BAREMETAL-MULTI-LP64: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv64imac/lp64{{/|\\\\}}crtend.o"
 
 // RUN: %clang %s -### -no-canonical-prefixes -fuse-ld=ld \
-// RUN:   -target riscv64-unknown-elf --sysroot= -march=rv64imafdc -mabi=lp64d \
+// RUN:   -target riscv64-unknown-elf --rtlib=platform --sysroot= \
+// RUN:   -march=rv64imafdc -mabi=lp64d \
 // RUN:   --gcc-toolchain=%S/Inputs/multilib_riscv_elf_sdk 2>&1 \
 // RUN:   | FileCheck -check-prefix=C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D %s
 
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "-fuse-init-array"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/bin{{/|\\\\}}ld"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "-m" "elf64lriscv"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv64imafdc/lp64d{{/|\\\\}}crt0.o"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv64imafdc/lp64d{{/|\\\\}}crtbegin.o"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "-L{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/../../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
 // C-RV64IMAFDC-BAREMETAL-MULTI-ILP64D: "{{.*}}/Inputs/multilib_riscv_elf_sdk/lib/gcc/riscv64-unknown-elf/8.2.0/rv64imafdc/lp64d{{/|\\\\}}crtend.o"
 
+// Check that --rtlib can be used to override the used runtime library
+// RUN: %clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv64-unknown-elf --rtlib=libgcc 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV64-RTLIB-LIBGCC-LP64 %s
+// C-RV64-RTLIB-LIBGCC-LP64: "{{.*}}crt0.o"
+// C-RV64-RTLIB-LIBGCC-LP64: "{{.*}}crtbegin.o"
+// C-RV64-RTLIB-LIBGCC-LP64: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
+// C-RV64-RTLIB-LIBGCC-LP64: "{{.*}}crtend.o"
+
+// RUN: %clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv64-unknown-elf --rtlib=compiler-rt 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV64-RTLIB-COMPILERRT-LP64 %s
+// C-RV64-RTLIB-COMPILERRT-LP64: "{{.*}}crt0.o"
+// C-RV64-RTLIB-COMPILERRT-LP64: "{{.*}}clang_rt.crtbegin-riscv64.o"
+// C-RV64-RTLIB-COMPILERRT-LP64: "--start-group" "-lc" "-lgloss" "--end-group" "{{.*}}libclang_rt.builtins-riscv64.a"
+// C-RV64-RTLIB-COMPILERRT-LP64: "{{.*}}clang_rt.crtend-riscv64.o"
+
 // RUN: %clang -target riscv64 %s -emit-llvm -S -o - | FileCheck %s
 
 typedef __builtin_va_list va_list;
 typedef __SIZE_TYPE__ size_t;
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
 typedef __WCHAR_TYPE__ wchar_t;
 typedef __WINT_TYPE__ wint_t;