Add LLVM 21

[kammce]

• LLVM 21.1.1 from ARM fork has LLVM
• LLVM 21.1.6 with the broadest set of platforms supported

[kammce]

We are encountering this problem:

[1/4] Scanning /home/runner/work/llvm-toolchain/llvm-toolchain/all/test_package/main.cpp for CXX dependencies
FAILED: [code=1] CMakeFiles/test_package.dir/main.cpp.obj.ddi 
"/home/runner/.conan2/p/b/llvm-9f680d0cf9e21/p/bin/clang-scan-deps" -format=p1689 -- /home/runner/.conan2/p/b/llvm-9f680d0cf9e21/p/bin/clang++ -D_LIBCPP_HAS_NO_THREADS=1  -stdlib=libc++ -flto  -ffunction-sections  -fdata-sections  -target armv6m-none-eabi -mcpu=cortex-m0plus -mfloat-abi=soft -O3 -DNDEBUG -std=c++23 -stdlib=libc++ -x c++ /home/runner/work/llvm-toolchain/llvm-toolchain/all/test_package/main.cpp -c -o CMakeFiles/test_package.dir/main.cpp.obj -resource-dir "/home/runner/.conan2/p/b/llvm-9f680d0cf9e21/p/lib/clang/21" -MT CMakeFiles/test_package.dir/main.cpp.obj.ddi -MD -MF CMakeFiles/test_package.dir/main.cpp.obj.ddi.d > CMakeFiles/test_package.dir/main.cpp.obj.ddi.tmp && mv CMakeFiles/test_package.dir/main.cpp.obj.ddi.tmp CMakeFiles/test_package.dir/main.cpp.obj.ddi
/home/runner/.conan2/p/b/llvm-9f680d0cf9e21/p/bin/../lib/clang-runtimes/multilib.yaml:47:3: error: unknown key 'IncludeDirs'
  IncludeDirs:
  ^~~~~~~~~~~
/home/runner/.conan2/p/b/llvm-9f680d0cf9e21/p/bin/../lib/clang-runtimes/multilib.yaml:21:1: error: multilib "aarch64-none-elf/aarch64a_exn_rtti_unaligned" specifies undefined group name "stdlibs"
MultilibVersion: '1.0'
^
/home/runner/.conan2/p/b/llvm-9f680d0cf9e21/p/bin/../lib/clang-runtimes/multilib.yaml:47:3: error: unknown key 'IncludeDirs'
  IncludeDirs:
  ^~~~~~~~~~~
/home/runner/.conan2/p/b/llvm-9f680d0cf9e21/p/bin/../lib/clang-runtimes/multilib.yaml:21:1: error: multilib "aarch64-none-elf/aarch64a_exn_rtti_unaligned" specifies undefined group name "stdlibs"
MultilibVersion: '1.0'
^
Error while scanning dependencies for /home/runner/work/llvm-toolchain/llvm-toolchain/all/test_package/main.cpp:
/home/runner/work/llvm-toolchain/llvm-toolchain/all/test_package/main.cpp:1:10: fatal error: 'cstdio' file not found
ninja: build stopped: subcommand failed.

ERROR: llvm-toolchain/21 (test package): Error in build() method, line 21
	cmake.build()
	ConanException: Error 1 while executing

Found here https://github.com/libhal/llvm-toolchain/actions/runs/20183711173/job/57971416572

Here is the llvm 21 multilib.yaml file.
And here is the llvm 20 multilib.yaml

This seems to be an issue clang-scan-deps not understanding what the "IncludeDirs" field means within the multilib.yaml file.

[kammce]

I will personally pause working on this until a later time. The purpose of bringing this version in was to see if it could solve a linker bug with cortex m0, m0+ and m1 where coroutines require a tailcall optimization that isn't possible, causing lld to produce a stacktrace like so:

FAILED: [code=1] test_package 
: && /home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/clang++ -stdlib=libc++ -flto  -ffunction-sections  -fdata-sections  -target armv6m-none-eabi -mcpu=cortex-m0 -mfloat-abi=soft -g -fuse-ld=lld -flto -Wl,--gc-sections -Wl,--default-script=picolibcpp.ld -target armv6m-none-eabi -mcpu=cortex-m0 -mfloat-abi=soft -nostartfiles -lcrt0-semihost -lsemihost -Xlinker --dependency-file=CMakeFiles/test_package.dir/link.d CMakeFiles/test_package.dir/main.cpp.obj -o test_package  /home/runner/.conan2/p/b/async7b8b9909f4702/p/lib/libasync_context.a  /home/runner/.conan2/p/stron24ff64b07689d/p/lib/libstrong_ptr.a && :
LLVM ERROR: failed to perform tail call elimination on a call site marked musttail
PLEASE submit a bug report to https://github.com/arm/arm-toolchain/issues and include the crash backtrace.
Stack dump:
0.	Program arguments: /home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld --gc-sections --default-script=picolibcpp.ld -lcrt0-semihost -lsemihost --dependency-file=CMakeFiles/test_package.dir/link.d CMakeFiles/test_package.dir/main.cpp.obj /home/runner/.conan2/p/b/async7b8b9909f4702/p/lib/libasync_context.a /home/runner/.conan2/p/stron24ff64b07689d/p/lib/libstrong_ptr.a -Bstatic -EL -L/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/../lib/clang-runtimes/arm-none-eabi/armv6m_soft_nofp_exn_rtti/lib -L/home/runner/.conan2/p/b/llvm-42b0471356906/p/lib/clang/20/lib/armv6m-unknown-none-eabi -L/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/../lib/clang-runtimes/arm-none-eabi/armv6m_soft_nofp_exn_rtti/lib -lc++ -lm -lc /home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/../lib/clang-runtimes/arm-none-eabi/armv6m_soft_nofp_exn_rtti/lib/libclang_rt.builtins.a -plugin-opt=mcpu=cortex-m0 -plugin-opt=-function-sections=1 -plugin-opt=-data-sections=1 --target2=rel -o test_package
1.	Running pass 'Function Pass Manager' on module 'ld-temp.o'.
2.	Running pass 'ARM Instruction Selection' on function '@_Z17coro_double_delayRN5async2v0W13async_context7contextE.resume'
 #0 0x000055fe826264f7 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x6104f7)
 #1 0x000055fe8262432e llvm::sys::RunSignalHandlers() (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x60e32e)
 #2 0x000055fe82626e7a SignalHandler(int) Signals.cpp:0:0
 #3 0x00007fcd40845330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
 #4 0x00007fcd4089eb2c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9eb2c)
 #5 0x00007fcd4084527e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
 #6 0x00007fcd408288ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
 #7 0x000055fe825d89d3 llvm::report_fatal_error(llvm::Twine const&, bool) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x5c29d3)
 #8 0x000055fe825d8826 (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x5c2826)
 #9 0x000055fe82e04d85 (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0xdeed85)
#10 0x000055fe83119f4f llvm::TargetLowering::LowerCallTo(llvm::TargetLowering::CallLoweringInfo&) const (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x1103f4f)
#11 0x000055fe83139376 llvm::SelectionDAGBuilder::lowerInvokable(llvm::TargetLowering::CallLoweringInfo&, llvm::BasicBlock const*) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x1123376)
#12 0x000055fe83121db7 llvm::SelectionDAGBuilder::LowerCallTo(llvm::CallBase const&, llvm::SDValue, bool, bool, llvm::BasicBlock const*, llvm::TargetLowering::PtrAuthInfo const*) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x110bdb7)
#13 0x000055fe8310c5ba llvm::SelectionDAGBuilder::visitCall(llvm::CallInst const&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x10f65ba)
#14 0x000055fe831007f1 llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x10ea7f1)
#15 0x000055fe831a7998 llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator_w_bits<llvm::ilist_detail::node_options<llvm::Instruction, false, false, void, true, llvm::BasicBlock>, false, true>, llvm::ilist_iterator_w_bits<llvm::ilist_detail::node_options<llvm::Instruction, false, false, void, true, llvm::BasicBlock>, false, true>, bool&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x1191998)
#16 0x000055fe831a75c9 llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x11915c9)
#17 0x000055fe831a52bd llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x118f2bd)
#18 0x000055fe82ddf4b1 (anonymous namespace)::ARMDAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) ARMISelDAGToDAG.cpp:0:0
#19 0x000055fe831a3861 llvm::SelectionDAGISelLegacy::runOnMachineFunction(llvm::MachineFunction&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x118d861)
#20 0x000055fe835e401a llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x15ce01a)
#21 0x000055fe84b35dd6 llvm::FPPassManager::runOnFunction(llvm::Function&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x2b1fdd6)
#22 0x000055fe84b3ccb3 llvm::FPPassManager::runOnModule(llvm::Module&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x2b26cb3)
#23 0x000055fe84b36abc llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x2b20abc)
#24 0x000055fe83344499 codegen(llvm::lto::Config const&, llvm::TargetMachine*, std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>, unsigned int, llvm::Module&, llvm::ModuleSummaryIndex const&) LTOBackend.cpp:0:0
#25 0x000055fe83343712 llvm::lto::backend(llvm::lto::Config const&, std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>, unsigned int, llvm::Module&, llvm::ModuleSummaryIndex&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x132d712)
#26 0x000055fe8332fe61 llvm::lto::LTO::runRegularLTO(std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x1319e61)
#27 0x000055fe8332f627 llvm::lto::LTO::run(std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>, llvm::FileCache) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x1319627)
#28 0x000055fe827df845 lld::elf::BitcodeCompiler::compile() (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x7c9845)
#29 0x000055fe8276158d void lld::elf::LinkerDriver::compileBitcodeFiles<llvm::object::ELFType<(llvm::endianness)1, false>>(bool) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x74b58d)
#30 0x000055fe827487e8 void lld::elf::LinkerDriver::link<llvm::object::ELFType<(llvm::endianness)1, false>>(llvm::opt::InputArgList&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x7327e8)
#31 0x000055fe827364d3 lld::elf::LinkerDriver::linkerMain(llvm::ArrayRef<char const*>) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x7204d3)
#32 0x000055fe82732ba5 lld::elf::link(llvm::ArrayRef<char const*>, llvm::raw_ostream&, llvm::raw_ostream&, bool, bool) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x71cba5)
#33 0x000055fe8265a7f5 lld::unsafeLldMain(llvm::ArrayRef<char const*>, llvm::raw_ostream&, llvm::raw_ostream&, llvm::ArrayRef<lld::DriverDef>, bool) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x6447f5)
#34 0x000055fe825bd929 lld_main(int, char**, llvm::ToolContext const&) (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x5a7929)
#35 0x000055fe825bde37 main (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x5a7e37)
#36 0x00007fcd4082a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
#37 0x00007fcd4082a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
#38 0x000055fe825bd585 _start (/home/runner/.conan2/p/b/llvm-42b0471356906/p/bin/ld.lld+0x5a7585)
clang++: error: unable to execute command: Aborted (core dumped)
clang++: error: ld.lld command failed due to signal (use -v to see invocation)
ninja: build stopped: subcommand failed.

Observed here: https://github.com/libhal/async_context/actions/runs/20182742390/job/57946614876#logs