Invalid usage of the XADD return value

[arieleiz]

When building an eBPF program, I get the final error:

fatal error: error in backend: line 37: Invalid usage of the XADD return value
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: clang -O2 -mcpu=v1 -I./bpftool/src/libbpf/include/ -I./ -D__TARGET_ARCH_x86=1 -target bpfel -c /home/user/ebpf/src2/ebpfcode.c -o /home/user/ebpf/src2/bpf_bpfel.o -fno-ident -fdebug-prefix-map=/home/user/ebpf/src2=. -fdebug-compilation-dir . -g "-D__BPF_TARGET_MISSING=\"GCC error \\\"The eBPF is using target specific macros, please provide -target that is not bpf, bpfel or bpfeb\\\"\"" -MD -MP -MF/tmp/bpf2go1503467571
1.      <eof> parser at end of file
2.      Code generation
3.      Running pass 'Function Pass Manager' on module '/home/user/ebpf/src2/ebpfcode.c'.
4.      Running pass 'BPF PreEmit Checking' on function '@next_event_id'
 #0 0x00007f2f77abbe1a llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/lib64/libLLVM-17.so+0x8bbe1a)
 #1 0x00007f2f77ab97a4 llvm::sys::RunSignalHandlers() (/lib64/libLLVM-17.so+0x8b97a4)
 #2 0x00007f2f779f07e2 (/lib64/libLLVM-17.so+0x7f07e2)
 #3 0x00007f2f779f079f (/lib64/libLLVM-17.so+0x7f079f)
 #4 0x00007f2f77ab5c1d (/lib64/libLLVM-17.so+0x8b5c1d)
 #5 0x0000000000412eb7 (/usr/bin/clang-17+0x412eb7)
 #6 0x00007f2f77a02137 llvm::report_fatal_error(llvm::Twine const&, bool) (/lib64/libLLVM-17.so+0x802137)
 #7 0x00007f2f7a9ea9e7 (/lib64/libLLVM-17.so+0x37ea9e7)
 #8 0x00007f2f77ef568c llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/lib64/libLLVM-17.so+0xcf568c)
 #9 0x00007f2f77c325b5 llvm::FPPassManager::runOnFunction(llvm::Function&) (/lib64/libLLVM-17.so+0xa325b5)
#10 0x00007f2f77c39393 llvm::FPPassManager::runOnModule(llvm::Module&) (/lib64/libLLVM-17.so+0xa39393)
#11 0x00007f2f77c32c6a llvm::legacy::PassManagerImpl::run(llvm::Module&) (/lib64/libLLVM-17.so+0xa32c6a)
#12 0x00007f2f7f36e825 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream>>) (/lib64/libclang-cpp.so.17+0x1b6e825)
#13 0x00007f2f7f76b048 (/lib64/libclang-cpp.so.17+0x1f6b048)
#14 0x00007f2f7e117526 clang::ParseAST(clang::Sema&, bool, bool) (/lib64/libclang-cpp.so.17+0x917526)
#15 0x00007f2f8032dc86 clang::FrontendAction::Execute() (/lib64/libclang-cpp.so.17+0x2b2dc86)
#16 0x00007f2f8029ae40 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/lib64/libclang-cpp.so.17+0x2a9ae40)
#17 0x00007f2f803ae6d4 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/lib64/libclang-cpp.so.17+0x2bae6d4)
#18 0x0000000000412911 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/usr/bin/clang-17+0x412911)
#19 0x000000000040fd25 (/usr/bin/clang-17+0x40fd25)
#20 0x00007f2f7fed4bfd (/lib64/libclang-cpp.so.17+0x26d4bfd)
#21 0x00007f2f779f0774 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/lib64/libLLVM-17.so+0x7f0774)
#22 0x00007f2f7fed4627 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (/lib64/libclang-cpp.so.17+0x26d4627)
#23 0x00007f2f7fe9afee clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/lib64/libclang-cpp.so.17+0x269afee)
#24 0x00007f2f7fe9b257 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/lib64/libclang-cpp.so.17+0x269b257)
#25 0x00007f2f7feb85da clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/lib64/libclang-cpp.so.17+0x26b85da)
#26 0x000000000040f568 clang_main(int, char**, llvm::ToolContext const&) (/usr/bin/clang-17+0x40f568)
#27 0x000000000041c036 main (/usr/bin/clang-17+0x41c036)
#28 0x00007f2f76a3feb0 __libc_start_call_main (/lib64/libc.so.6+0x3feb0)
#29 0x00007f2f76a3ff60 __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x3ff60)
#30 0x000000000040c425 _start (/usr/bin/clang-17+0x40c425)
Error: can't execute clang: exit status 1

[EugeneZelenko]

Could you please try 18 or main branch? https://godbolt.org should be helpful.

[arieleiz]

Yes, it happens with 18 and main.
Code to reproduce in godbolt.org:

typedef unsigned int u32;
volatile u32 GLOBAL_EVENT_ID = 0;

u32 next_event_id()
{
    return __sync_fetch_and_add(&GLOBAL_EVENT_ID, 1);
}

Here is with trunk branch:

fatal error: error in backend: line 6: Invalid usage of the XADD return value
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-trunk/bin/clang++ -g -o /app/output.s -S -target bpf -fcolor-diagnostics -fno-crash-diagnostics -O2 <source>
1.	<eof> parser at end of file
2.	Code generation
3.	Running pass 'Function Pass Manager' on module '<source>'.
4.	Running pass 'BPF PreEmit Checking' on function '@_Z13next_event_idv'
 #0 0x0000000003702088 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3702088)
 #1 0x00000000037001d4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x37001d4)
 #2 0x0000000003655113 llvm::CrashRecoveryContext::HandleExit(int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3655113)
 #3 0x00000000036f77ae llvm::sys::Process::Exit(int, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x36f77ae)
 #4 0x0000000000c5af16 (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc5af16)
 #5 0x000000000365e1c3 llvm::report_fatal_error(llvm::Twine const&, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x365e1c3)
 #6 0x00000000017a670d (anonymous namespace)::BPFMIPreEmitChecking::processAtomicInsts() (.isra.0) BPFMIChecking.cpp:0:0
 #7 0x0000000002b8ea10 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
 #8 0x00000000030b9df2 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x30b9df2)
 #9 0x00000000030b9f71 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x30b9f71)
#10 0x00000000030bbc20 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x30bbc20)
#11 0x0000000003982f1e clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream>>, clang::BackendConsumer*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3982f1e)
#12 0x0000000003f7f625 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f7f625)
#13 0x0000000005e5938c clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5e5938c)
#14 0x0000000003f7fea5 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f7fea5)
#15 0x000000000421ae61 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x421ae61)
#16 0x00000000041a0d3b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x41a0d3b)
#17 0x00000000042ff5c3 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x42ff5c3)
#18 0x0000000000c5cc9c cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc5cc9c)
#19 0x0000000000c56d9d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#20 0x0000000003fc8869 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#21 0x0000000003655013 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3655013)
#22 0x0000000003fc8a89 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#23 0x0000000003f8f097 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f8f097)
#24 0x0000000003f8fa4d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f8fa4d)
#25 0x0000000003f997fc clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f997fc)
#26 0x0000000000c5a141 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc5a141)
#27 0x0000000000b3be64 main (/opt/compiler-explorer/clang-trunk/bin/clang+++0xb3be64)
#28 0x000072553e029d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#29 0x000072553e029e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#30 0x0000000000c5683e _start (/opt/compiler-explorer/clang-trunk/bin/clang+++0xc5683e)
Compiler returned: 1

Here with 18.1:

fatal error: error in backend: line 6: Invalid usage of the XADD return value
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-18.1.0/bin/clang++ -g -o /app/output.s -S -target bpf -fcolor-diagnostics -fno-crash-diagnostics -O2 <source>
1.	<eof> parser at end of file
2.	Code generation
3.	Running pass 'Function Pass Manager' on module '<source>'.
4.	Running pass 'BPF PreEmit Checking' on function '@_Z13next_event_idv'
 #0 0x000000000351ae38 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x351ae38)
 #1 0x0000000003518f84 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3518f84)
 #2 0x0000000003467543 llvm::CrashRecoveryContext::HandleExit(int) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3467543)
 #3 0x000000000351097e llvm::sys::Process::Exit(int, bool) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x351097e)
 #4 0x0000000000c17976 (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0xc17976)
 #5 0x0000000003470593 llvm::report_fatal_error(llvm::Twine const&, bool) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3470593)
 #6 0x0000000001713a85 (anonymous namespace)::BPFMIPreEmitChecking::processAtomicInsts() (.isra.0) BPFMIChecking.cpp:0:0
 #7 0x00000000029bc2f0 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
 #8 0x0000000002ee69e2 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x2ee69e2)
 #9 0x0000000002ee6b61 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x2ee6b61)
#10 0x0000000002ee87e0 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x2ee87e0)
#11 0x000000000378ad99 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream>>, clang::BackendConsumer*) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x378ad99)
#12 0x0000000003d5b2d1 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3d5b2d1)
#13 0x0000000005b965d9 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x5b965d9)
#14 0x0000000003d5a725 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3d5a725)
#15 0x0000000003fe2aa1 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3fe2aa1)
#16 0x0000000003f6010b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3f6010b)
#17 0x00000000040c2473 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x40c2473)
#18 0x0000000000c19746 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0xc19746)
#19 0x0000000000c1211d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#20 0x0000000003da1979 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#21 0x0000000003467443 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3467443)
#22 0x0000000003da1b99 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#23 0x0000000003d69d17 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3d69d17)
#24 0x0000000003d6a6cd clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3d6a6cd)
#25 0x0000000003d7445c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0x3d7445c)
#26 0x0000000000c16a21 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0xc16a21)
#27 0x0000000000b0fa84 main (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0xb0fa84)
#28 0x000077e129429d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#29 0x000077e129429e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#30 0x0000000000c1191e _start (/opt/compiler-explorer/clang-18.1.0/bin/clang+++0xc1191e)
Compiler returned: 1

[arieleiz]

This might be a clue: If I change __sync_fetch_and_add() to __sync_bool_compare_and_swap() ,
I get

/home/user/ebpf/src2/ebpfcode.c:50:12: error: Unsupported atomic operations, please use 64 bit version
   50 |         if(__sync_bool_compare_and_swap(id_ptr, id, id + 1))
      |            ^
fatal error: error in backend: Cannot select: 0x1863040: i64,ch = AtomicCmpSwap<(load store seq_cst seq_cst (s32) on %ir.2)> 0x1862fd0:1, 0x1862f60, 0x1862fd0, 0x1862da0, ./ebpfcode.c:50:12
  0x1862f60: i64,ch = CopyFromReg 0x14cb830, Register:i64 %0, ./ebpfcode.c:49:18
    0x18629b0: i64 = Register %0
  0x1862fd0: i64,ch = load<(volatile load (s32) from %ir.2, !tbaa !155), zext from i32> 0x14cb830, 0x1862f60, undef:i64, ./ebpfcode.c:49:18
    0x1862f60: i64,ch = CopyFromReg 0x14cb830, Register:i64 %0, ./ebpfcode.c:49:18
      0x18629b0: i64 = Register %0
    0x1862e10: i64 = undef
  0x1862da0: i64 = add 0x1862fd0, Constant:i64<1>, ./ebpfcode.c:50:56
    0x1862fd0: i64,ch = load<(volatile load (s32) from %ir.2, !tbaa !155), zext from i32> 0x14cb830, 0x1862f60, undef:i64, ./ebpfcode.c:49:18
      0x1862f60: i64,ch = CopyFromReg 0x14cb830, Register:i64 %0, ./ebpfcode.c:49:18
        0x18629b0: i64 = Register %0
      0x1862e10: i64 = undef
    0x1862d30: i64 = Constant<1>
In function: next_event_id
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: clang -O2 -mcpu=v1 -I./bpftool/src/libbpf/include/ -I./ -D__TARGET_ARCH_x86=1 -target bpfel -c /home/user/ebpf/src2/ebpfcode.c -o /home/user/ebpf/src2/bpf_bpfel.o -fno-ident -fdebug-prefix-map=/home/user/ebpf/src2=. -fdebug-compilation-dir . -g "-D__BPF_TARGET_MISSING=\"GCC error \\\"The eBPF is using target specific macros, please provide -target that is not bpf, bpfel or bpfeb\\\"\"" -MD -MP -MF/tmp/bpf2go530511853
1.      <eof> parser at end of file
2.      Code generation
3.      Running pass 'Function Pass Manager' on module '/home/user/ebpf/src2/ebpfcode.c'.
4.      Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@next_event_id'
 #0 0x00007fbc3d8bbe1a llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/lib64/libLLVM-17.so+0x8bbe1a)
 #1 0x00007fbc3d8b97a4 llvm::sys::RunSignalHandlers() (/lib64/libLLVM-17.so+0x8b97a4)
 #2 0x00007fbc3d7f07e2 (/lib64/libLLVM-17.so+0x7f07e2)
 #3 0x00007fbc3d7f079f (/lib64/libLLVM-17.so+0x7f079f)
 #4 0x00007fbc3d8b5c1d (/lib64/libLLVM-17.so+0x8b5c1d)
 #5 0x0000000000412eb7 (/usr/bin/clang-17+0x412eb7)
 #6 0x00007fbc3d802137 llvm::report_fatal_error(llvm::Twine const&, bool) (/lib64/libLLVM-17.so+0x802137)
 #7 0x00007fbc3e22160d llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*) (/lib64/libLLVM-17.so+0x122160d)
 #8 0x00007fbc3e220ab8 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*, unsigned int) (/lib64/libLLVM-17.so+0x1220ab8)
 #9 0x00007fbc407cf51a (/lib64/libLLVM-17.so+0x37cf51a)
#10 0x00007fbc3e2175df llvm::SelectionDAGISel::DoInstructionSelection() (/lib64/libLLVM-17.so+0x12175df)
#11 0x00007fbc3e216ade llvm::SelectionDAGISel::CodeGenAndEmitDAG() (/lib64/libLLVM-17.so+0x1216ade)
#12 0x00007fbc3e215ba1 llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) (/lib64/libLLVM-17.so+0x1215ba1)
#13 0x00007fbc3e213100 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) (/lib64/libLLVM-17.so+0x1213100)
#14 0x00007fbc3dcf568c llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/lib64/libLLVM-17.so+0xcf568c)
#15 0x00007fbc3da325b5 llvm::FPPassManager::runOnFunction(llvm::Function&) (/lib64/libLLVM-17.so+0xa325b5)
#16 0x00007fbc3da39393 llvm::FPPassManager::runOnModule(llvm::Module&) (/lib64/libLLVM-17.so+0xa39393)
#17 0x00007fbc3da32c6a llvm::legacy::PassManagerImpl::run(llvm::Module&) (/lib64/libLLVM-17.so+0xa32c6a)
#18 0x00007fbc4516e825 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream>>) (/lib64/libclang-cpp.so.17+0x1b6e825)
#19 0x00007fbc4556b048 (/lib64/libclang-cpp.so.17+0x1f6b048)
#20 0x00007fbc43f17526 clang::ParseAST(clang::Sema&, bool, bool) (/lib64/libclang-cpp.so.17+0x917526)
#21 0x00007fbc4612dc86 clang::FrontendAction::Execute() (/lib64/libclang-cpp.so.17+0x2b2dc86)
#22 0x00007fbc4609ae40 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/lib64/libclang-cpp.so.17+0x2a9ae40)
#23 0x00007fbc461ae6d4 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/lib64/libclang-cpp.so.17+0x2bae6d4)
#24 0x0000000000412911 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/usr/bin/clang-17+0x412911)
#25 0x000000000040fd25 (/usr/bin/clang-17+0x40fd25)
#26 0x00007fbc45cd4bfd (/lib64/libclang-cpp.so.17+0x26d4bfd)
#27 0x00007fbc3d7f0774 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/lib64/libLLVM-17.so+0x7f0774)
#28 0x00007fbc45cd4627 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (/lib64/libclang-cpp.so.17+0x26d4627)
#29 0x00007fbc45c9afee clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/lib64/libclang-cpp.so.17+0x269afee)
#30 0x00007fbc45c9b257 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/lib64/libclang-cpp.so.17+0x269b257)
#31 0x00007fbc45cb85da clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/lib64/libclang-cpp.so.17+0x26b85da)
#32 0x000000000040f568 clang_main(int, char**, llvm::ToolContext const&) (/usr/bin/clang-17+0x40f568)
#33 0x000000000041c036 main (/usr/bin/clang-17+0x41c036)
#34 0x00007fbc3c83feb0 __libc_start_call_main (/lib64/libc.so.6+0x3feb0)
#35 0x00007fbc3c83ff60 __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x3ff60)
#36 0x000000000040c425 _start (/usr/bin/clang-17+0x40c425)
clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)
clang version 17.0.6 (RESF 17.0.6-5.el9)
Target: bpfel
Thread model: posix
InstalledDir: /usr/bin
...

[inclyc]

Reduced:

@GLOBAL_EVENT_ID = global i32 0, align 4

define i32 @next_event_id() #0 {
entry:
  %0 = atomicrmw add ptr @GLOBAL_EVENT_ID, i32 1 seq_cst, align 4
  ret i32 %0
}

Currently, BPF has XADD (locked add) insn support and the
asm looks like:

  lock *(u32 *)(r1 + 0) += r2
  lock *(u64 *)(r1 + 0) += r2

The instruction itself does not have a return value.

At the source code level, users often use

  __sync_fetch_and_add()

which eventually translates to XADD. The return value of
__sync_fetch_and_add() is supposed to be the old value
in the xadd memory location. Since BPF::XADD insn does not support such a return value, if such an illegal usage
pattern is detected, a fatal error will be reported like

  line 4: Invalid usage of the XADD return value

if compiled with -g, or

Invalid usage of the XADD return value

if compiled without -g.

fatal error: error in backend: Cannot select: 0x1863040: i64,ch = AtomicCmpSwap<(load store seq_cst seq_cst (s32) on %ir.2)> 0x1862fd0:1, 0x1862f60, 0x1862fd0, 0x1862da0, ./ebpfcode.c:50:12

This is indeed another bug though.