git: 4fc1fdd206c3 - main - Merge commit c1d26c3c2510 from llvm git (by Nikolas Klauser):
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Date: Sat, 25 Apr 2026 14:20:21 UTC
The branch main has been updated by dim:
URL: https://cgit.FreeBSD.org/src/commit/?id=4fc1fdd206c3db60ca521e3966f31044c7711398
commit 4fc1fdd206c3db60ca521e3966f31044c7711398
Author: Dimitry Andric <dim@FreeBSD.org>
AuthorDate: 2026-03-12 13:24:01 +0000
Commit: Dimitry Andric <dim@FreeBSD.org>
CommitDate: 2026-04-25 14:14:22 +0000
Merge commit c1d26c3c2510 from llvm git (by Nikolas Klauser):
[libc++] Fix iostream size ABI break (#185839)
In #124103 we changed the size of various iostream objects, which turns
out to be ABI breaking when compiling non-PIE code.
This ABI break is safe to fix, since for any programs allocating more
memory for the iostream objects, the remaining bytes are simply unused
now.
Fixes #185724
This fixes the ABI break that causes programs that use the standard
streams to terminate in various interesting ways, usually by throwing an
unexpected std::bad_cast exception.
PR: 292067
MFC after: 1 month
---
contrib/llvm-project/libcxx/src/iostream.cpp | 93 +++++++++++++++++-----------
1 file changed, 56 insertions(+), 37 deletions(-)
diff --git a/contrib/llvm-project/libcxx/src/iostream.cpp b/contrib/llvm-project/libcxx/src/iostream.cpp
index 416725235c34..b216c6ad35da 100644
--- a/contrib/llvm-project/libcxx/src/iostream.cpp
+++ b/contrib/llvm-project/libcxx/src/iostream.cpp
@@ -16,24 +16,40 @@
_LIBCPP_BEGIN_NAMESPACE_STD
+// This file implements the various stream objects provided inside <iostream>. We're doing some ODR violations in here,
+// so this quite fragile. Specifically, the size of the stream objects (i.e. cout, cin etc.) needs to stay the same.
+// For that reason, we have `stream` and `stream_data` separated into two objects. The public `stream` objects only
+// contain the actual stream, while the private `stream_data` objects contains the `basic_streambuf` we're using as well
+// as the mbstate_t. `stream_data` objects are only accessible within the library, so they aren't ABI sensitive and we
+// can change them as we want.
+
+template <class StreamT>
+union stream {
+ constexpr stream() {}
+ stream(const stream&) = delete;
+ stream& operator=(const stream&) = delete;
+ constexpr ~stream() {}
+
+ StreamT value;
+};
+
template <class StreamT, class BufferT>
union 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;
BufferT buffer;
mbstate_t mb;
};
-
- void init(FILE* stdstream) {
- mb = {};
- std::construct_at(&buffer, stdstream, &mb);
- std::construct_at(&stream, &buffer);
- }
};
+template <class StreamT, class BufferT>
+void init_stream(FILE* stdstream, stream<StreamT>& stream, stream_data<StreamT, BufferT>& data) {
+ data.mb = {};
+ std::construct_at(&data.buffer, stdstream, &data.mb);
+ std::construct_at(&stream.value, &data.buffer);
+}
+
#define CHAR_MANGLING_char "D"
#define CHAR_MANGLING_wchar_t "_W"
#define CHAR_MANGLING(CharT) CHAR_MANGLING_##CharT
@@ -46,25 +62,28 @@ union stream_data {
#ifdef _LIBCPP_ABI_MICROSOFT
# define STREAM(StreamT, BufferT, CharT, var) \
- STRING_DATA_CONSTINIT stream_data<StreamT<CharT>, BufferT<CharT>> var __asm__( \
+ STRING_DATA_CONSTINIT stream_data<StreamT<CharT>, BufferT<CharT>> var##_data; \
+ _LIBCPP_EXPORTED_FROM_ABI STRING_DATA_CONSTINIT stream<StreamT<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) STRING_DATA_CONSTINIT stream_data<StreamT<CharT>, BufferT<CharT>> var
+# define STREAM(StreamT, BufferT, CharT, var) \
+ STRING_DATA_CONSTINIT stream_data<StreamT<CharT>, BufferT<CharT>> var##_data; \
+ _LIBCPP_EXPORTED_FROM_ABI STRING_DATA_CONSTINIT stream<StreamT<CharT>> var
#endif
// These definitions and the declarations in <iostream> technically cause ODR violations, since they have different
// types (stream_data and {i,o}stream respectively). This means that <iostream> should never be included in this TU.
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_istream, __stdinbuf, char, cin);
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_ostream, __stdoutbuf, char, cout);
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_ostream, __stdoutbuf, char, cerr);
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_ostream, __stdoutbuf, char, clog);
+STREAM(basic_istream, __stdinbuf, char, cin);
+STREAM(basic_ostream, __stdoutbuf, char, cout);
+STREAM(basic_ostream, __stdoutbuf, char, cerr);
+STREAM(basic_ostream, __stdoutbuf, char, clog);
#if _LIBCPP_HAS_WIDE_CHARACTERS
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_istream, __stdinbuf, wchar_t, wcin);
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_ostream, __stdoutbuf, wchar_t, wcout);
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_ostream, __stdoutbuf, wchar_t, wcerr);
-_LIBCPP_EXPORTED_FROM_ABI STREAM(basic_ostream, __stdoutbuf, wchar_t, wclog);
+STREAM(basic_istream, __stdinbuf, wchar_t, wcin);
+STREAM(basic_ostream, __stdoutbuf, wchar_t, wcout);
+STREAM(basic_ostream, __stdoutbuf, wchar_t, wcerr);
+STREAM(basic_ostream, __stdoutbuf, wchar_t, wclog);
#endif // _LIBCPP_HAS_WIDE_CHARACTERS
// Pretend we're inside a system header so the compiler doesn't flag the use of the init_priority
@@ -98,34 +117,34 @@ public:
DoIOSInit::DoIOSInit() {
force_locale_initialization();
- cin.init(stdin);
- cout.init(stdout);
- cerr.init(stderr);
- clog.init(stderr);
+ init_stream(stdin, cin, cin_data);
+ init_stream(stdout, cout, cout_data);
+ init_stream(stderr, cerr, cerr_data);
+ init_stream(stderr, clog, clog_data);
- cin.stream.tie(&cout.stream);
- std::unitbuf(cerr.stream);
- cerr.stream.tie(&cout.stream);
+ cin.value.tie(&cout.value);
+ std::unitbuf(cerr.value);
+ cerr.value.tie(&cout.value);
#if _LIBCPP_HAS_WIDE_CHARACTERS
- wcin.init(stdin);
- wcout.init(stdout);
- wcerr.init(stderr);
- wclog.init(stderr);
-
- wcin.stream.tie(&wcout.stream);
- std::unitbuf(wcerr.stream);
- wcerr.stream.tie(&wcout.stream);
+ init_stream(stdin, wcin, wcin_data);
+ init_stream(stdout, wcout, wcout_data);
+ init_stream(stderr, wcerr, wcerr_data);
+ init_stream(stderr, wclog, wclog_data);
+
+ wcin.value.tie(&wcout.value);
+ std::unitbuf(wcerr.value);
+ wcerr.value.tie(&wcout.value);
#endif
}
DoIOSInit::~DoIOSInit() {
- cout.stream.flush();
- clog.stream.flush();
+ cout.value.flush();
+ clog.value.flush();
#if _LIBCPP_HAS_WIDE_CHARACTERS
- wcout.stream.flush();
- wclog.stream.flush();
+ wcout.value.flush();
+ wclog.value.flush();
#endif
}