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[libunwind] Remove MSVC C11 stdalign.h and stdatomic.h fake headers #129246

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[libunwind] Remove MSVC C11 stdalign.h and stdatomic.h fake headers #129246

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95c70c8
[libunwind] Remove MSVC C11 stdalign.h and stdatomic.h fake headers
mdh1418 May 19, 2026
1305dba
[libunwind] Address PR review feedback
mdh1418 Jun 10, 2026
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14 changes: 0 additions & 14 deletions src/native/external/libunwind/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -74,20 +74,6 @@ if ("${CMAKE_GENERATOR}" MATCHES "^Visual Studio.*$")
set(HAVE_ELF_H 1)
set(HAVE_ENDIAN_H 1)

# MSVC compiler is currently missing C11 stdalign.h header
# Fake it until support is added
check_include_files(stdalign.h HAVE_STDALIGN_H)
if (NOT HAVE_STDALIGN_H)
configure_file(include/remote/win/fakestdalign.h.in ${CMAKE_CURRENT_BINARY_DIR}/include/stdalign.h)
endif (NOT HAVE_STDALIGN_H)

# MSVC compiler is currently missing C11 stdatomic.h header
# Fake it until support is added
check_include_files(stdatomic.h HAVE_STDATOMIC_H)
if (NOT HAVE_STDATOMIC_H)
configure_file(include/remote/win/fakestdatomic.h.in ${CMAKE_CURRENT_BINARY_DIR}/include/stdatomic.h)
endif (NOT HAVE_STDATOMIC_H)

# MSVC compiler is currently missing C11 _Thread_local
check_c_source_compiles("void main() { _Thread_local int a; }" HAVE_THREAD_LOCAL)
if (NOT HAVE_THREAD_LOCAL)
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9 changes: 0 additions & 9 deletions src/native/external/libunwind/include/remote/win/fakestdalign.h.in
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36 changes: 0 additions & 36 deletions src/native/external/libunwind/include/remote/win/fakestdatomic.h.in
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12 changes: 12 additions & 0 deletions src/native/external/libunwind_extras/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,18 @@ if(CLR_CMAKE_HOST_WIN32)
# Assume we are using default MSVC compiler
add_compile_options(/permissive-)

# Enable C11 atomics so libunwind's <stdatomic.h> usage
# (e.g. atomic_compare_exchange_strong in Gaddress_validator.c) compiles
# against MSVC's real header instead of a generated fake.
# /std:c11 is already implied by CMAKE_C_STANDARD=11 set in libunwind/CMakeLists.txt.

@github-actions github-actions Bot Jul 19, 2026

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Nit: this comment states /std:c11 is implied by CMAKE_C_STANDARD=11 set in libunwind/CMakeLists.txt, but that upstream file is not part of the cross-DAC build. src/coreclr/CMakeLists.txt adds libunwind_extras via add_subdirectory(...external/libunwind_extras ...), and this libunwind_extras/CMakeLists.txt does not set CMAKE_C_STANDARD. The flag works because current MSVC defaults to a C11/C17 language mode for .c files, not because of that setting. Consider correcting the comment so future readers don't rely on a CMAKE_C_STANDARD value that isn't actually in effect here.

# CMAKE_C_COMPILER_ID is used instead of MSVC so that clang-cl (which sets

@jkotas jkotas Jun 10, 2026 •
edited
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We do not support clang-cl and I expect we would need number of changes to actually support it. This can be simplified to just use /experimental:c11atomics unconditionally.

# MSVC=TRUE but does not accept /experimental:c11atomics) is excluded.
# The COMPILE_LANGUAGE:C generator expression scopes the flag to C sources
# so it is not passed to C++ compilation (e.g. remote-unwind.cpp).
if(CMAKE_C_COMPILER_ID STREQUAL "MSVC")
add_compile_options($<$<COMPILE_LANGUAGE:C>:/experimental:c11atomics>)
endif()

# include paths
include_directories(${CLR_SRC_NATIVE_DIR}/external/libunwind/include/tdep)
include_directories(${CLR_SRC_NATIVE_DIR}/external/libunwind/include)
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13 changes: 0 additions & 13 deletions src/native/external/libunwind_extras/configure.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -7,19 +7,6 @@ if(CLR_CMAKE_HOST_WIN32)
set(HAVE_ELF_H 1)
set(HAVE_ENDIAN_H 1)

# MSVC compiler is currently missing C11 stdalign.h header
# Fake it until support is added
check_include_files(stdalign.h HAVE_STDALIGN_H)
if (NOT HAVE_STDALIGN_H)
configure_file(${CLR_SRC_NATIVE_DIR}/external/libunwind/include/remote/win/fakestdalign.h.in ${CMAKE_CURRENT_BINARY_DIR}/include/stdalign.h COPYONLY)
endif (NOT HAVE_STDALIGN_H)

# MSVC compiler is currently missing C11 stdatomic.h header
check_c_source_compiles("#include <stdatomic.h> void main() { _Atomic int a; }" HAVE_STDATOMIC_H)
if (NOT HAVE_STDATOMIC_H)
configure_file(${CLR_SRC_NATIVE_DIR}/external/libunwind/include/remote/win/fakestdatomic.h.in ${CMAKE_CURRENT_BINARY_DIR}/include/stdatomic.h COPYONLY)
endif (NOT HAVE_STDATOMIC_H)

# MSVC compiler is currently missing C11 _Thread_local
check_c_source_compiles("void main() { _Thread_local int a; }" HAVE_THREAD_LOCAL)
if (NOT HAVE_THREAD_LOCAL)
Expand Down
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