[llvm-branch-commits] [libcxx] release/22.x: [libc++] Fix iostream size ABI break (#185839) (PR #186061)

via llvm-branch-commits llvm-branch-commits at lists.llvm.org
Thu Mar 12 02:25:57 PDT 2026


https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/186061

Backport c1d26c3c25106be2bc5b2b5a440faa5b93488de5

Requested by: @philnik777

>From 32d4fe9a0919362cb9d1b1ed1a99685575767f1f Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Thu, 12 Mar 2026 10:18:25 +0100
Subject: [PATCH] [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

(cherry picked from commit c1d26c3c25106be2bc5b2b5a440faa5b93488de5)
---
 ...bcxxabi.v1.stable.exceptions.nonew.abilist | 16 ++--
 ...bcxxabi.v1.stable.exceptions.nonew.abilist | 16 ++--
 ...bcxxabi.v1.stable.exceptions.nonew.abilist | 16 ++--
 ...bcxxabi.v1.stable.exceptions.nonew.abilist | 16 ++--
 ...xxabi.v1.stable.noexceptions.nonew.abilist | 16 ++--
 libcxx/src/iostream.cpp                       | 93 +++++++++++--------
 6 files changed, 96 insertions(+), 77 deletions(-)

diff --git a/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
index abbcc5c14b544..767a3a9d0da06 100644
--- a/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1226,7 +1226,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk133__atomic_wait_native_with_timeoutILj4EEEvPKvS2_y', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk134__construct_barrier_algorithm_baseERi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk139__atomic_wait_global_table_with_timeoutEPKviy', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk13cinE', 'size': 148, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk13cinE', 'size': 88, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk13pmr15memory_resourceD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk13pmr15memory_resourceD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk13pmr15memory_resourceD2Ev', 'type': 'FUNC'}
@@ -1294,9 +1294,9 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk14__fs10filesystem8__removeERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14__fs10filesystem8__renameERKNS1_4pathES4_PNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14__fs10filesystem8__statusERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14cerrE', 'size': 136, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14clogE', 'size': 136, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14coutE', 'size': 136, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14cerrE', 'size': 84, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14clogE', 'size': 84, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14coutE', 'size': 84, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stodERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPj', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stodERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPj', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stofERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPj', 'type': 'FUNC'}
@@ -1305,7 +1305,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk14stoiERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPji', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stolERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPji', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stolERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPji', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14wcinE', 'size': 148, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14wcinE', 'size': 88, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15alignEjjRPvRj', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15ctypeIcE10table_sizeE', 'size': 4, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15ctypeIcE13classic_tableEv', 'type': 'FUNC'}
@@ -1330,9 +1330,9 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk15stollERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPji', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15stoulERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPji', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15stoulERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPji', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk15wcerrE', 'size': 136, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk15wclogE', 'size': 136, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk15wcoutE', 'size': 136, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk15wcerrE', 'size': 84, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk15wclogE', 'size': 84, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk15wcoutE', 'size': 84, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk16__clocEv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk16__itoa8__u32toaEjPc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk16__itoa8__u64toaEyPc', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
index 6c437f9adea48..c3826e77c101f 100644
--- a/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1226,7 +1226,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk133__atomic_wait_native_with_timeoutILm4EEEvPKvS2_m', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk134__construct_barrier_algorithm_baseERl', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk139__atomic_wait_global_table_with_timeoutEPKvim', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk13cinE', 'size': 280, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk13cinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk13pmr15memory_resourceD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk13pmr15memory_resourceD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk13pmr15memory_resourceD2Ev', 'type': 'FUNC'}
@@ -1294,9 +1294,9 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk14__fs10filesystem8__removeERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14__fs10filesystem8__renameERKNS1_4pathES4_PNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14__fs10filesystem8__statusERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14cerrE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14clogE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14coutE', 'size': 264, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14cerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14clogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14coutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stodERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stodERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stofERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
@@ -1305,7 +1305,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk14stoiERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stolERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk14stolERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk14wcinE', 'size': 280, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk14wcinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15alignEmmRPvRm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15ctypeIcE10table_sizeE', 'size': 8, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15ctypeIcE13classic_tableEv', 'type': 'FUNC'}
@@ -1330,9 +1330,9 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk15stollERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15stoulERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk15stoulERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt6__ndk15wcerrE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk15wclogE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt6__ndk15wcoutE', 'size': 264, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk15wcerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk15wclogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt6__ndk15wcoutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk16__clocEv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk16__itoa8__u32toaEjPc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk16__itoa8__u64toaEmPc', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
index 017b6d33c4262..b27dab3d9203e 100644
--- a/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1240,7 +1240,7 @@
 {'is_defined': True, 'name': '_ZNSt3__133__atomic_wait_native_with_timeoutILm8EEEvPKvS2_m', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__134__construct_barrier_algorithm_baseERl', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__139__atomic_wait_global_table_with_timeoutEPKvlm', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__13cinE', 'size': 400, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__13cinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD2Ev', 'type': 'FUNC'}
@@ -1308,9 +1308,9 @@
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__removeERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__renameERKNS1_4pathES4_PNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__statusERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__14cerrE', 'size': 384, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__14clogE', 'size': 384, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__14coutE', 'size': 384, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14cerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14clogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14coutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__14stodERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stodERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stofERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
@@ -1319,7 +1319,7 @@
 {'is_defined': True, 'name': '_ZNSt3__14stoiERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stolERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stolERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__14wcinE', 'size': 400, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14wcinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__15alignEmmRPvRm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15ctypeIcE10table_sizeE', 'size': 8, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__15ctypeIcE13classic_tableEv', 'type': 'FUNC'}
@@ -1344,9 +1344,9 @@
 {'is_defined': True, 'name': '_ZNSt3__15stollERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15stoulERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15stoulERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__15wcerrE', 'size': 384, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__15wclogE', 'size': 384, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__15wcoutE', 'size': 384, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wcerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wclogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wcoutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__16__itoa8__u32toaEjPc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__16__itoa8__u64toaEmPc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__16__sortIRNS_6__lessIaaEEPaEEvT0_S5_T_', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
index 363fa42975b8e..e5372de54c40e 100644
--- a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1238,7 +1238,7 @@
 {'is_defined': True, 'name': '_ZNSt3__133__atomic_wait_native_with_timeoutILm4EEEvPKvS2_m', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__134__construct_barrier_algorithm_baseERl', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__139__atomic_wait_global_table_with_timeoutEPKvim', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__13cinE', 'size': 280, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__13cinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD2Ev', 'type': 'FUNC'}
@@ -1306,9 +1306,9 @@
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__removeERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__renameERKNS1_4pathES4_PNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__statusERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__14cerrE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__14clogE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__14coutE', 'size': 264, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14cerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14clogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14coutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__14stodERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stodERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stofERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
@@ -1317,7 +1317,7 @@
 {'is_defined': True, 'name': '_ZNSt3__14stoiERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stolERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stolERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__14wcinE', 'size': 280, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14wcinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__15alignEmmRPvRm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15ctypeIcE10table_sizeE', 'size': 8, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__15ctypeIcE13classic_tableEv', 'type': 'FUNC'}
@@ -1342,9 +1342,9 @@
 {'is_defined': True, 'name': '_ZNSt3__15stollERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15stoulERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15stoulERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__15wcerrE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__15wclogE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__15wcoutE', 'size': 264, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wcerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wclogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wcoutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__16__clocEv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__16__itoa8__u32toaEjPc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__16__itoa8__u64toaEmPc', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
index cf4668a2dea21..4def06bc737ce 100644
--- a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
@@ -1209,7 +1209,7 @@
 {'is_defined': True, 'name': '_ZNSt3__133__atomic_wait_native_with_timeoutILm4EEEvPKvS2_m', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__134__construct_barrier_algorithm_baseERl', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__139__atomic_wait_global_table_with_timeoutEPKvim', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__13cinE', 'size': 280, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__13cinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__13pmr15memory_resourceD2Ev', 'type': 'FUNC'}
@@ -1277,9 +1277,9 @@
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__removeERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__renameERKNS1_4pathES4_PNS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14__fs10filesystem8__statusERKNS1_4pathEPNS_10error_codeE', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__14cerrE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__14clogE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__14coutE', 'size': 264, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14cerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14clogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14coutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__14stodERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stodERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stofERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPm', 'type': 'FUNC'}
@@ -1288,7 +1288,7 @@
 {'is_defined': True, 'name': '_ZNSt3__14stoiERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stolERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__14stolERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__14wcinE', 'size': 280, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__14wcinE', 'size': 168, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__15alignEmmRPvRm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15ctypeIcE10table_sizeE', 'size': 8, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__15ctypeIcE13classic_tableEv', 'type': 'FUNC'}
@@ -1313,9 +1313,9 @@
 {'is_defined': True, 'name': '_ZNSt3__15stollERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15stoulERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPmi', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__15stoulERKNS_12basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEEEPmi', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__15wcerrE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__15wclogE', 'size': 264, 'type': 'OBJECT'}
-{'is_defined': True, 'name': '_ZNSt3__15wcoutE', 'size': 264, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wcerrE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wclogE', 'size': 160, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZNSt3__15wcoutE', 'size': 160, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__16__clocEv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__16__itoa8__u32toaEjPc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__16__itoa8__u64toaEmPc', 'type': 'FUNC'}
diff --git a/libcxx/src/iostream.cpp b/libcxx/src/iostream.cpp
index 416725235c340..b216c6ad35daf 100644
--- a/libcxx/src/iostream.cpp
+++ b/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 at 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 @@ class DoIOSInit {
 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
 }
 



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