powerpc64-ibm-aix: the .weak assembler directive is not supported

[folkertdev]

the .weak assembler directive is currently not supported by LLVM (although it is documented https://www.ibm.com/docs/en/ssw_aix_71/assembler/assembler_pdf.pdf).

In contrast, the .weak_definition directive is accepted by the assembly parser, but crashes LLVM later on.

Therefore it is currently impossible to define weak symbols using inline assembly.

---

the .weak_definition attribute fails with (https://godbolt.org/z/rderToPx4)

clang version 21.0.0git (https://github.com/llvm/llvm-project.git 5422e2c)
Target: powerpc64-ibm-aix
Thread model: posix
InstalledDir: /opt/compiler-explorer/clang-trunk-20250306/bin
(in-process)
"/opt/compiler-explorer/clang-trunk-20250306/bin/clang-21" -cc1 -triple powerpc64-ibm-aix -emit-obj -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name example.c -mrelocation-model pic -pic-level 2 -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -fno-verbose-asm -mconstructor-aliases -fxl-pragma-pack -fno-sized-deallocation -target-cpu pwr7 -mfloat-abi hard -gstrict-dwarf -gno-column-info -debug-info-kind=constructor -dwarf-version=3 -fdebug-compilation-dir=/app -v -fdata-sections -fcoverage-compilation-dir=/app -resource-dir /opt/compiler-explorer/clang-trunk-20250306/lib/clang/21 -internal-isystem /opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include/ppc_wrappers -internal-isystem /opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include -internal-isystem /usr/include -ferror-limit 19 -fno-signed-char -fno-use-cxa-atexit -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcolor-diagnostics -o /app/output.s -x c
clang -cc1 version 21.0.0git based upon LLVM 21.0.0git default target x86_64-unknown-linux-gnu
#include "..." search starts here:
#include <...> search starts here:
/opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include/ppc_wrappers
/opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include
/usr/include
End of search list.
fatal error: error in backend: Not implemented yet.
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 -fno-verbose-asm -c -target powerpc64 -fcolor-diagnostics -fno-crash-diagnostics -target powerpc64-ibm-aix -v <source>
1.	<eof> parser at end of file
2.	Code generation
 #0 0x0000000003b50668 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3b50668)
 #1 0x0000000003b4e7ac llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3b4e7ac)
 #2 0x0000000003a9e083 llvm::CrashRecoveryContext::HandleExit(int) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3a9e083)
 #3 0x0000000003b4623e llvm::sys::Process::Exit(int, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3b4623e)
 #4 0x0000000000d611db LLVMErrorHandler(void*, char const*, bool) cc1_main.cpp:0:0
 #5 0x0000000003aa8153 llvm::report_fatal_error(llvm::Twine const&, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3aa8153)
 #6 0x0000000003aa82b8 (/opt/compiler-explorer/clang-trunk/bin/clang+0x3aa82b8)
 #7 0x00000000038740e0 llvm::MCXCOFFStreamer::emitXCOFFRefDirective(llvm::MCSymbol const*) (/opt/compiler-explorer/clang-trunk/bin/clang+0x38740e0)
 #8 0x00000000038cb850 bool llvm::function_ref<bool ()>::callback_fn<(anonymous namespace)::AsmParser::parseDirectiveSymbolAttribute(llvm::MCSymbolAttr)::'lambda'()>(long) AsmParser.cpp:0:0
 #9 0x00000000038f0fec llvm::MCAsmParser::parseMany(llvm::function_ref<bool ()>, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x38f0fec)
#10 0x00000000038defb0 (anonymous namespace)::AsmParser::parseStatement((anonymous namespace)::ParseStatementInfo&, llvm::MCAsmParserSemaCallback*) AsmParser.cpp:0:0
#11 0x00000000038d1e62 (anonymous namespace)::AsmParser::Run(bool, bool) AsmParser.cpp:0:0
#12 0x0000000004a7ab6c llvm::AsmPrinter::emitInlineAsm(llvm::StringRef, llvm::MCSubtargetInfo const&, llvm::MCTargetOptions const&, llvm::MDNode const*, llvm::InlineAsm::AsmDialect) const (/opt/compiler-explorer/clang-trunk/bin/clang+0x4a7ab6c)
#13 0x0000000004a6fc39 llvm::AsmPrinter::doInitialization(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/clang+0x4a6fc39)
#14 0x0000000001ef16f9 (anonymous namespace)::PPCAIXAsmPrinter::doInitialization(llvm::Module&) PPCAsmPrinter.cpp:0:0
#15 0x00000000034aec28 llvm::FPPassManager::doInitialization(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/clang+0x34aec28)
#16 0x00000000034ba02e llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/clang+0x34ba02e)
#17 0x0000000003df7c2e clang::emitBackendOutput(clang::CompilerInstance&, clang::CodeGenOptions&, 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+0x3df7c2e)
#18 0x00000000044cbac5 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-trunk/bin/clang+0x44cbac5)
#19 0x000000000603bfcc clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x603bfcc)
#20 0x00000000044cc1e5 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+0x44cc1e5)
#21 0x00000000047a6431 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+0x47a6431)
#22 0x000000000472706b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-trunk/bin/clang+0x472706b)
#23 0x0000000004893423 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+0x4893423)
#24 0x0000000000d63411 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+0xd63411)
#25 0x0000000000d5bc1d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#26 0x0000000004518759 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
#27 0x0000000003a9df83 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3a9df83)
#28 0x0000000004518979 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
#29 0x00000000044dc79d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+0x44dc79d)
#30 0x00000000044dd731 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+0x44dd731)
#31 0x00000000044e7b6c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-trunk/bin/clang+0x44e7b6c)
#32 0x0000000000d600d1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-trunk/bin/clang+0xd600d1)
#33 0x0000000000c21ad4 main (/opt/compiler-explorer/clang-trunk/bin/clang+0xc21ad4)
#34 0x00007e785ce29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#35 0x00007e785ce29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#36 0x0000000000d5b6b5 _start (/opt/compiler-explorer/clang-trunk/bin/clang+0xd5b6b5)

clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)
Compiler returned: 70

this came up here rust-lang/rust#137816
cc @daltenty

[llvmbot]

@llvm/issue-subscribers-backend-powerpc

Author: Folkert de Vries (folkertdev)

the `.weak` assembler directive is currently not supported by LLVM (although it is documented https://www.ibm.com/docs/en/ssw_aix_71/assembler/assembler_pdf.pdf).

In contrast, the .weak_definition directive is accepted by the assembly parser, but crashes LLVM later on.

Therefore it is currently impossible to define weak symbols using inline assembly.

---

the .weak_definition attribute fails with (https://godbolt.org/z/rderToPx4)

clang version 21.0.0git (https://github.com/llvm/llvm-project.git 5422e2c)
Target: powerpc64-ibm-aix
Thread model: posix
InstalledDir: /opt/compiler-explorer/clang-trunk-20250306/bin
(in-process)
"/opt/compiler-explorer/clang-trunk-20250306/bin/clang-21" -cc1 -triple powerpc64-ibm-aix -emit-obj -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name example.c -mrelocation-model pic -pic-level 2 -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -fno-verbose-asm -mconstructor-aliases -fxl-pragma-pack -fno-sized-deallocation -target-cpu pwr7 -mfloat-abi hard -gstrict-dwarf -gno-column-info -debug-info-kind=constructor -dwarf-version=3 -fdebug-compilation-dir=/app -v -fdata-sections -fcoverage-compilation-dir=/app -resource-dir /opt/compiler-explorer/clang-trunk-20250306/lib/clang/21 -internal-isystem /opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include/ppc_wrappers -internal-isystem /opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include -internal-isystem /usr/include -ferror-limit 19 -fno-signed-char -fno-use-cxa-atexit -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcolor-diagnostics -o /app/output.s -x c <source>
clang -cc1 version 21.0.0git based upon LLVM 21.0.0git default target x86_64-unknown-linux-gnu
#include "..." search starts here:
#include <...> search starts here:
/opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include/ppc_wrappers
/opt/compiler-explorer/clang-trunk-20250306/lib/clang/21/include
/usr/include
End of search list.
fatal error: error in backend: Not implemented yet.
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 -fno-verbose-asm -c -target powerpc64 -fcolor-diagnostics -fno-crash-diagnostics -target powerpc64-ibm-aix -v <source>
1.	<eof> parser at end of file
2.	Code generation
 #<!-- -->0 0x0000000003b50668 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3b50668)
 #<!-- -->1 0x0000000003b4e7ac llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3b4e7ac)
 #<!-- -->2 0x0000000003a9e083 llvm::CrashRecoveryContext::HandleExit(int) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3a9e083)
 #<!-- -->3 0x0000000003b4623e llvm::sys::Process::Exit(int, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3b4623e)
 #<!-- -->4 0x0000000000d611db LLVMErrorHandler(void*, char const*, bool) cc1_main.cpp:0:0
 #<!-- -->5 0x0000000003aa8153 llvm::report_fatal_error(llvm::Twine const&amp;, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3aa8153)
 #<!-- -->6 0x0000000003aa82b8 (/opt/compiler-explorer/clang-trunk/bin/clang+0x3aa82b8)
 #<!-- -->7 0x00000000038740e0 llvm::MCXCOFFStreamer::emitXCOFFRefDirective(llvm::MCSymbol const*) (/opt/compiler-explorer/clang-trunk/bin/clang+0x38740e0)
 #<!-- -->8 0x00000000038cb850 bool llvm::function_ref&lt;bool ()&gt;::callback_fn&lt;(anonymous namespace)::AsmParser::parseDirectiveSymbolAttribute(llvm::MCSymbolAttr)::'lambda'()&gt;(long) AsmParser.cpp:0:0
 #<!-- -->9 0x00000000038f0fec llvm::MCAsmParser::parseMany(llvm::function_ref&lt;bool ()&gt;, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x38f0fec)
#<!-- -->10 0x00000000038defb0 (anonymous namespace)::AsmParser::parseStatement((anonymous namespace)::ParseStatementInfo&amp;, llvm::MCAsmParserSemaCallback*) AsmParser.cpp:0:0
#<!-- -->11 0x00000000038d1e62 (anonymous namespace)::AsmParser::Run(bool, bool) AsmParser.cpp:0:0
#<!-- -->12 0x0000000004a7ab6c llvm::AsmPrinter::emitInlineAsm(llvm::StringRef, llvm::MCSubtargetInfo const&amp;, llvm::MCTargetOptions const&amp;, llvm::MDNode const*, llvm::InlineAsm::AsmDialect) const (/opt/compiler-explorer/clang-trunk/bin/clang+0x4a7ab6c)
#<!-- -->13 0x0000000004a6fc39 llvm::AsmPrinter::doInitialization(llvm::Module&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+0x4a6fc39)
#<!-- -->14 0x0000000001ef16f9 (anonymous namespace)::PPCAIXAsmPrinter::doInitialization(llvm::Module&amp;) PPCAsmPrinter.cpp:0:0
#<!-- -->15 0x00000000034aec28 llvm::FPPassManager::doInitialization(llvm::Module&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+0x34aec28)
#<!-- -->16 0x00000000034ba02e llvm::legacy::PassManagerImpl::run(llvm::Module&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+0x34ba02e)
#<!-- -->17 0x0000000003df7c2e clang::emitBackendOutput(clang::CompilerInstance&amp;, clang::CodeGenOptions&amp;, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr&lt;llvm::vfs::FileSystem&gt;, std::unique_ptr&lt;llvm::raw_pwrite_stream, std::default_delete&lt;llvm::raw_pwrite_stream&gt;&gt;, clang::BackendConsumer*) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3df7c2e)
#<!-- -->18 0x00000000044cbac5 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+0x44cbac5)
#<!-- -->19 0x000000000603bfcc clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+0x603bfcc)
#<!-- -->20 0x00000000044cc1e5 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+0x44cc1e5)
#<!-- -->21 0x00000000047a6431 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+0x47a6431)
#<!-- -->22 0x000000000472706b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+0x472706b)
#<!-- -->23 0x0000000004893423 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+0x4893423)
#<!-- -->24 0x0000000000d63411 cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+0xd63411)
#<!-- -->25 0x0000000000d5bc1d ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->26 0x0000000004518759 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::'lambda'()&gt;(long) Job.cpp:0:0
#<!-- -->27 0x0000000003a9df83 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-trunk/bin/clang+0x3a9df83)
#<!-- -->28 0x0000000004518979 clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (.part.0) Job.cpp:0:0
#<!-- -->29 0x00000000044dc79d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+0x44dc79d)
#<!-- -->30 0x00000000044dd731 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+0x44dd731)
#<!-- -->31 0x00000000044e7b6c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+0x44e7b6c)
#<!-- -->32 0x0000000000d600d1 clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-trunk/bin/clang+0xd600d1)
#<!-- -->33 0x0000000000c21ad4 main (/opt/compiler-explorer/clang-trunk/bin/clang+0xc21ad4)
#<!-- -->34 0x00007e785ce29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#<!-- -->35 0x00007e785ce29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#<!-- -->36 0x0000000000d5b6b5 _start (/opt/compiler-explorer/clang-trunk/bin/clang+0xd5b6b5)

clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)
Compiler returned: 70

this came up here rust-lang/rust#137816
cc @daltenty