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[libc++] Fix initialization-order-fiasco with iostream.cpp constructors #126995

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Merged
merged 10 commits into from
Feb 16, 2025
Merged

[libc++] Fix initialization-order-fiasco with iostream.cpp constructors #126995

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[𝘀𝗽𝗿] initial version
vitalybuka Feb 13, 2025
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with fix
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constinit
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={}
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CLANG_ONLY
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no {}
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14 changes: 10 additions & 4 deletions libcxx/src/iostream.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD

template <class StreamT, class BufferT>
union stream_data {
stream_data() {}
~stream_data() {}
constexpr stream_data() {}
constexpr ~stream_data() {}
struct {
// The stream has to be the first element, since that's referenced by the stream declarations in <iostream>
StreamT stream;
Expand All @@ -38,13 +38,19 @@ union stream_data {
#define CHAR_MANGLING_wchar_t "_W"
#define CHAR_MANGLING(CharT) CHAR_MANGLING_##CharT

#ifdef _LIBCPP_COMPILER_CLANG_BASED
# define STRING_DATA_CONSTINIT constinit
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can't figure out how to make GCC happy,
all the time: error: ‘constinit’ variable ‘std::__1::cin’ does not have a constant initializer

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Hmm. I'll try to figure something out tomorrow for this. Either a bug against one of the compilers or some code changes should happen here. I guess a CWG issue would also be possible.

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Can we land this one in meantime?

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I'm fine with that.

#else
# define STRING_DATA_CONSTINIT
#endif

#ifdef _LIBCPP_ABI_MICROSOFT
# define STREAM(StreamT, BufferT, CharT, var) \
stream_data<StreamT<CharT>, BufferT<CharT>> var __asm__( \
STRING_DATA_CONSTINIT stream_data<StreamT<CharT>, BufferT<CharT>> var __asm__( \
"?" #var "@" ABI_NAMESPACE_STR "@std@@3V?$" #StreamT \
"@" CHAR_MANGLING(CharT) "U?$char_traits@" CHAR_MANGLING(CharT) "@" ABI_NAMESPACE_STR "@std@@@12@A")
#else
# define STREAM(StreamT, BufferT, CharT, var) stream_data<StreamT<CharT>, BufferT<CharT>> var
# define STREAM(StreamT, BufferT, CharT, var) STRING_DATA_CONSTINIT stream_data<StreamT<CharT>, BufferT<CharT>> var
#endif

// These definitions and the declarations in <iostream> technically cause ODR violations, since they have different
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20 changes: 20 additions & 0 deletions ...test/std/input.output/iostreams.base/ios.base/ios.types/ios_Init/ios_Init.global.pass.cpp
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@@ -0,0 +1,20 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include <iostream>

// FIXME: Remove after issue https://github.com/llvm/llvm-project/issues/127348 resolved.
extern "C" const char* __asan_default_options() { return "check_initialization_order=true:strict_init_order=true"; }

// Test that ios used from globals constructors doesn't trigger Asan initialization-order-fiasco.

struct Global {
Global() { std::cout << "Hello!"; }
} global;

int main(int, char**) { return 0; }