-Wduplicate-decl-specifier and LLVM "error in backend: Unsupported expression in static initializer" crash trying to enable CONFIG_USE_X86_SEG_SUPPORT

[nathanchance]

On top of current -tip, which has some fixes for CONFIG_USE_X86_SEG_SUPPORT, attempting to enable it for Clang with

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c62db6b853d7..e8eb2e06ad2c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2429,10 +2429,10 @@ source "kernel/livepatch/Kconfig"
 endmenu

 config CC_HAS_NAMED_AS
-       def_bool CC_IS_GCC && GCC_VERSION >= 90100
+       def_bool (CC_IS_GCC && GCC_VERSION >= 90100) || (CC_IS_CLANG && CLANG_VERSION >= 190000)

 config CC_HAS_NAMED_AS_FIXED_SANITIZERS
-       def_bool CC_IS_GCC && GCC_VERSION >= 130300
+       def_bool !CC_IS_GCC || (CC_IS_GCC && GCC_VERSION >= 130300)

 config USE_X86_SEG_SUPPORT
        def_bool y

results in

In file included from arch/x86/kernel/asm-offsets.c:9:
In file included from include/linux/crypto.h:15:
In file included from include/linux/completion.h:12:
In file included from include/linux/swait.h:7:
In file included from include/linux/spinlock.h:56:
In file included from include/linux/preempt.h:79:
In file included from arch/x86/include/asm/preempt.h:7:
arch/x86/include/asm/current.h:47:10: error: multiple identical address spaces specified for type [-Werror,-Wduplicate-decl-specifier]
   47 |                 return this_cpu_read_const(const_pcpu_hot.current_task);
      |                        ^
arch/x86/include/asm/percpu.h:462:34: note: expanded from macro 'this_cpu_read_const'
  462 | #define this_cpu_read_const(pcp)        __raw_cpu_read(, pcp)
      |                                         ^
arch/x86/include/asm/percpu.h:432:30: note: expanded from macro '__raw_cpu_read'
  432 |         *(qual __my_cpu_type(pcp) *)__my_cpu_ptr(&(pcp));               \
      |                                     ^
arch/x86/include/asm/percpu.h:99:28: note: expanded from macro '__my_cpu_ptr'
   99 | #define __my_cpu_ptr(ptr)       (__my_cpu_type(*ptr)*)(__force uintptr_t)(ptr)
      |                                  ^
arch/x86/include/asm/percpu.h:98:40: note: expanded from macro '__my_cpu_type'
   98 | #define __my_cpu_type(var)      typeof(var) __percpu_seg_override
      |                                             ^
arch/x86/include/asm/percpu.h:45:31: note: expanded from macro '__percpu_seg_override'
   45 | #define __percpu_seg_override   __seg_gs
      |                                 ^
<built-in>:343:33: note: expanded from macro '__seg_gs'
  343 | #define __seg_gs __attribute__((address_space(256)))
      |                                 ^

I think this should be resolved with __typeof_unqual__, which was recently added to LLVM by myself in llvm/llvm-project@cc308f6 (hence the 190000 check above) and its use has been talked about on LKML. This diff shuts up the warning above (may or may not be actually correct)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 20696df5d567..fc77c99d2e80 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -95,7 +95,7 @@

 #endif /* CONFIG_SMP */

-#define __my_cpu_type(var)     typeof(var) __percpu_seg_override
+#define __my_cpu_type(var)     __typeof_unqual__(var) __percpu_seg_override
 #define __my_cpu_ptr(ptr)      (__my_cpu_type(*ptr)*)(__force uintptr_t)(ptr)
 #define __my_cpu_var(var)      (*__my_cpu_ptr(&(var)))
 #define __percpu_arg(x)                __percpu_prefix "%" #x

but I get a crash in arch/x86/kernel/cpu/common.c

fatal error: error in backend: Unsupported expression in static initializer: addrspacecast (ptr addrspace(256) @const_pcpu_hot to ptr)
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: /mnt/nvme/tmp/build/llvm-project/final/bin/clang --target=x86_64-linux-gnu -fintegrated-as -Werror=unknown-warning-option -Werror=ignored-optimization-argument -Werror=option-ignored -Werror=unused-command-line-argument -fmacro-prefix-map=/home/nathan/cbl/src/dev/linux-next/= -std=gnu11 -fshort-wchar -funsigned-char -fno-common -fno-PIE -fno-strict-aliasing -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -fcf-protection=branch -fno-jump-tables -m64 -falign-loops=1 -mno-80387 -mno-fp-ret-in-387 -mstack-alignment=8 -mskip-rax-setup -mtune=generic -mno-red-zone -mcmodel=kernel -Wno-sign-compare -fno-asynchronous-unwind-tables -mretpoline-external-thunk -mindirect-branch-cs-prefix -mfunction-return=thunk-extern -fpatchable-function-entry=16,16 -fno-delete-null-pointer-checks -O2 -fstack-protector-strong -fomit-frame-pointer -ftrivial-auto-var-init=zero -fno-stack-clash-protection -falign-functions=16 -fstrict-flex-arrays=3 -fno-strict-overflow -fno-stack-check -Wall -Wundef -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Werror=strict-prototypes -Wno-format-security -Wno-trigraphs -Wno-frame-address -Wno-address-of-packed-member -Wmissing-declarations -Wmissing-prototypes -Wframe-larger-than=2048 -Wno-gnu -Wno-unused-but-set-variable -Wno-unused-const-variable -Wvla -Wno-pointer-sign -Wcast-function-type -Wimplicit-fallthrough -Werror=date-time -Werror=incompatible-pointer-types -Wenum-conversion -Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-format-overflow -Wno-format-truncation -Wno-override-init -Wno-pointer-to-enum-cast -Wno-tautological-constant-out-of-range-compare -Wno-unaligned-access -Wno-cast-function-type-strict -Wno-enum-compare-conditional -Wno-enum-enum-conversion -Wno-missing-field-initializers -Wno-type-limits -Wno-shift-negative-value -Wno-sign-compare -Werror -nostdinc -I/home/nathan/cbl/src/dev/linux-next/arch/x86/include -I./arch/x86/include/generated -I/home/nathan/cbl/src/dev/linux-next/include -I./include -I/home/nathan/cbl/src/dev/linux-next/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/nathan/cbl/src/dev/linux-next/include/uapi -I./include/generated/uapi -include /home/nathan/cbl/src/dev/linux-next/include/linux/compiler-version.h -include /home/nathan/cbl/src/dev/linux-next/include/linux/kconfig.h -include /home/nathan/cbl/src/dev/linux-next/include/linux/compiler_types.h -D__KERNEL__ -I /home/nathan/cbl/src/dev/linux-next/arch/x86/kernel/cpu -I ./arch/x86/kernel/cpu -DKBUILD_MODFILE=\"arch/x86/kernel/cpu/common\" -DKBUILD_BASENAME=\"common\" -DKBUILD_MODNAME=\"common\" -D__KBUILD_MODNAME=kmod_common -c -Wp,-MMD,arch/x86/kernel/cpu/.common.o.d -fcolor-diagnostics -o arch/x86/kernel/cpu/common.o /home/nathan/cbl/src/dev/linux-next/arch/x86/kernel/cpu/common.c
1.	<eof> parser at end of file
2.	Code generation
 #0 0x0000557a7233aa18 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x534aa18)
 #1 0x0000557a7233859e llvm::sys::RunSignalHandlers() (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x534859e)
 #2 0x0000557a722ba2a7 (anonymous namespace)::CrashRecoveryContextImpl::HandleCrash(int, unsigned long) CrashRecoveryContext.cpp:0:0
 #3 0x0000557a722ba23f llvm::CrashRecoveryContext::HandleExit(int) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x52ca23f)
 #4 0x0000557a72334f07 llvm::sys::Process::Exit(int, bool) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5344f07)
 #5 0x0000557a704f85a3 (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x35085a3)
 #6 0x0000557a722bfe42 llvm::report_fatal_error(llvm::Twine const&, bool) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x52cfe42)
 #7 0x0000557a7322e423 llvm::AsmPrinter::lowerConstant(llvm::Constant const*) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x623e423)
 #8 0x0000557a7322e8b0 emitGlobalConstantImpl(llvm::DataLayout const&, llvm::Constant const*, llvm::AsmPrinter&, llvm::Constant const*, unsigned long, llvm::DenseMap<unsigned long, llvm::SmallVector<llvm::GlobalAlias const*, 1u>, llvm::DenseMapInfo<unsigned long, void>, llvm::detail::DenseMapPair<unsigned long, llvm::SmallVector<llvm::GlobalAlias const*, 1u>>>*) AsmPrinter.cpp:0:0
 #9 0x0000557a73220dd0 llvm::AsmPrinter::emitGlobalConstant(llvm::DataLayout const&, llvm::Constant const*, llvm::DenseMap<unsigned long, llvm::SmallVector<llvm::GlobalAlias const*, 1u>, llvm::DenseMapInfo<unsigned long, void>, llvm::detail::DenseMapPair<unsigned long, llvm::SmallVector<llvm::GlobalAlias const*, 1u>>>*) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x6230dd0)
#10 0x0000557a7322032a llvm::AsmPrinter::emitGlobalVariable(llvm::GlobalVariable const*) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x623032a)
#11 0x0000557a73229cfc llvm::AsmPrinter::doFinalization(llvm::Module&) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x6239cfc)
#12 0x0000557a71e7affa llvm::FPPassManager::doFinalization(llvm::Module&) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x4e8affa)
#13 0x0000557a71e73ace llvm::legacy::PassManagerImpl::run(llvm::Module&) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x4e83ace)
#14 0x0000557a72acadc1 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*) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5adadc1)
#15 0x0000557a72af017f clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5b0017f)
#16 0x0000557a73d8f9e9 clang::ParseAST(clang::Sema&, bool, bool) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x6d9f9e9)
#17 0x0000557a72eeb70f clang::FrontendAction::Execute() (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5efb70f)
#18 0x0000557a72e602fd clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5e702fd)
#19 0x0000557a72fa9bea clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5fb9bea)
#20 0x0000557a704f818f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x350818f)
#21 0x0000557a704f4919 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#22 0x0000557a72ce5619 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::$_0>(long) Job.cpp:0:0
#23 0x0000557a722ba1d6 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x52ca1d6)
#24 0x0000557a72ce4d23 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5cf4d23)
#25 0x0000557a72ca3b83 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5cb3b83)
#26 0x0000557a72ca3e37 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5cb3e37)
#27 0x0000557a72cc0da9 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x5cd0da9)
#28 0x0000557a704f40bc clang_main(int, char**, llvm::ToolContext const&) (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x35040bc)
#29 0x0000557a70503ba7 main (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x3513ba7)
#30 0x00007ff40e261cd0 (/usr/lib/libc.so.6+0x25cd0)
#31 0x00007ff40e261d8a __libc_start_main (/usr/lib/libc.so.6+0x25d8a)
#32 0x0000557a704f2365 _start (/mnt/nvme/tmp/build/llvm-project/final/bin/clang+0x3502365)
clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)
ClangBuiltLinux clang version 19.0.0git (https://github.com/llvm/llvm-project 5b702be1e80b8733786ac48ceaf04f2936616d1b)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /mnt/nvme/tmp/build/llvm-project/final/bin
clang: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang: note: diagnostic msg: /tmp/common-b4a03e.c
clang: note: diagnostic msg: /tmp/common-b4a03e.sh
clang: note: diagnostic msg: 

********************

The crash occurs without the __typeof_unqual__ diff if KCFLAGS=-Wno-duplicate-decl-specifier is passed, so it seems like the problems are unrelated.

I'll try to reduce something out for the crash later.

[nathanchance]

The -Wduplicate-decl-specifier instance can be worked around in the kernel: https://lore.kernel.org/lkml/[email protected]/

Uros reported the crash upstream and I reduced something down for the LLVM folks to take a look at: llvm/llvm-project#93449