release/19.x: [libc++] Avoid re-exporting a few specific symbols from libc++abi (#109054) #110677

llvmbot · 2024-10-01T13:45:56Z

Backport 677e8cd

Requested by: @ldionne

llvmbot · 2024-10-01T13:46:02Z

@var-const What do you think about merging this PR to the release branch?

llvmbot · 2024-10-01T13:46:33Z

@llvm/pr-subscribers-libcxx

Author: None (llvmbot)

Changes

Backport 677e8cd

Requested by: @ldionne

Full diff: https://github.com/llvm/llvm-project/pull/110677.diff

7 Files Affected:

(modified) libcxx/lib/abi/CHANGELOG.TXT (+30)
(modified) libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist (-7)
(modified) libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist (-7)
(modified) libcxxabi/lib/cxxabiv1.exp (-3)
(modified) libcxxabi/lib/itanium-base.exp (-1)
(added) libcxxabi/lib/symbols-not-reexported.exp (+13)
(modified) libcxxabi/src/CMakeLists.txt (+9-1)

diff --git a/libcxx/lib/abi/CHANGELOG.TXT b/libcxx/lib/abi/CHANGELOG.TXT
index 32526f1786c6d9..68c9d980a016ea 100644
--- a/libcxx/lib/abi/CHANGELOG.TXT
+++ b/libcxx/lib/abi/CHANGELOG.TXT
@@ -16,6 +16,36 @@ New entries should be added directly below the "Version" header.
 Version 19.0
 ------------
 
+* [libc++] Avoid re-exporting a few specific symbols from libc++abi
+
+  In 6a884a9aef39, I synchronized the export list of libc++abi to the
+  export list of libc++. From the linker's perspective, this caused
+  these symbols to be taken from libc++.dylib instead of libc++abi.dylib.
+
+  However, that can be problematic when back-deploying. Indeed, this means
+  that the linker will encode an undefined reference to be fullfilled by
+  libc++.dylib, but when backdeploying against an older system, that symbol
+  might only be available in libc++abi.dylib.
+
+  Most of the symbols that started being re-exported after 6a884a9aef39
+  turn out to be implementation details of libc++abi, so nobody really
+  depends on them and this back-deployment issue is inconsequential.
+
+  However, we ran into issues with a few of these symbols while testing
+  LLVM 19, which led to this patch.
+
+  In the future, a follow-up cleanup would be to stop exporting most of
+  the _cxxabiv1_foo_type_infoE symbols from both libc++abi and libc++
+  since they are implementation details that nobody should be relying
+  on.
+
+  <arch>-apple-darwin
+  -------------------
+  Symbol not reexported anymore: ___cxa_rethrow_primary_exception
+  Symbol not reexported anymore: __ZTIN10__cxxabiv117__class_type_infoE
+  Symbol not reexported anymore: __ZTIN10__cxxabiv120__si_class_type_infoE
+  Symbol not reexported anymore: __ZTIN10__cxxabiv121__vmi_class_type_infoE
+
 * [libc++] Always keep libc++abi re-exports up-to-date
 
   This patch makes sure that the set of libc++abi symbols re-exported from libc++
diff --git a/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
index 917388f86811fe..32acae46e292d7 100644
--- a/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -78,12 +78,9 @@
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIPDh', 'type': 'U'}
@@ -2002,12 +1999,9 @@
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTINSt12experimental15fundamentals_v112bad_any_castE', 'size': 0, 'type': 'OBJECT'}
@@ -2615,7 +2609,6 @@
 {'is_defined': True, 'name': '___cxa_new_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_pure_virtual', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_rethrow', 'type': 'I'}
-{'is_defined': True, 'name': '___cxa_rethrow_primary_exception', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_terminate_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw_bad_array_new_length', 'type': 'I'}
diff --git a/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
index defe235a283c21..7b5d77499d55fa 100644
--- a/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -78,12 +78,9 @@
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIPDh', 'type': 'U'}
@@ -2002,12 +1999,9 @@
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTINSt12experimental15fundamentals_v112bad_any_castE', 'size': 0, 'type': 'OBJECT'}
@@ -2649,7 +2643,6 @@
 {'is_defined': True, 'name': '___cxa_new_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_pure_virtual', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_rethrow', 'type': 'I'}
-{'is_defined': True, 'name': '___cxa_rethrow_primary_exception', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_terminate_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw_bad_array_new_length', 'type': 'I'}
diff --git a/libcxxabi/lib/cxxabiv1.exp b/libcxxabi/lib/cxxabiv1.exp
index b1bab45ef33479..0a22831a63d0bb 100644
--- a/libcxxabi/lib/cxxabiv1.exp
+++ b/libcxxabi/lib/cxxabiv1.exp
@@ -2,12 +2,9 @@
 __ZTIN10__cxxabiv116__enum_type_infoE
 __ZTIN10__cxxabiv116__shim_type_infoE
 __ZTIN10__cxxabiv117__array_type_infoE
-__ZTIN10__cxxabiv117__class_type_infoE
 __ZTIN10__cxxabiv117__pbase_type_infoE
 __ZTIN10__cxxabiv119__pointer_type_infoE
 __ZTIN10__cxxabiv120__function_type_infoE
-__ZTIN10__cxxabiv120__si_class_type_infoE
-__ZTIN10__cxxabiv121__vmi_class_type_infoE
 __ZTIN10__cxxabiv123__fundamental_type_infoE
 __ZTIN10__cxxabiv129__pointer_to_member_type_infoE
 
diff --git a/libcxxabi/lib/itanium-base.exp b/libcxxabi/lib/itanium-base.exp
index 002e062df423e7..0c23a19c94c528 100644
--- a/libcxxabi/lib/itanium-base.exp
+++ b/libcxxabi/lib/itanium-base.exp
@@ -12,7 +12,6 @@ ___cxa_guard_acquire
 ___cxa_guard_release
 ___cxa_increment_exception_refcount
 ___cxa_pure_virtual
-___cxa_rethrow_primary_exception
 ___cxa_throw_bad_array_new_length
 ___cxa_uncaught_exception
 ___cxa_uncaught_exceptions
diff --git a/libcxxabi/lib/symbols-not-reexported.exp b/libcxxabi/lib/symbols-not-reexported.exp
new file mode 100644
index 00000000000000..ea5d0b3fc15d78
--- /dev/null
+++ b/libcxxabi/lib/symbols-not-reexported.exp
@@ -0,0 +1,13 @@
+# These symbols are not re-exported from libc++ because providing a definition in libc++ causes
+# issues with some clients when backdeploying.
+
+# These symbols are implementation details of libc++abi, but they are referenced from UBSan
+# (which is a total hack). We'll need to figure out how to decouple UBSan from these details
+# before we can stop exporting them from libc++abi.
+__ZTIN10__cxxabiv117__class_type_infoE
+__ZTIN10__cxxabiv120__si_class_type_infoE
+__ZTIN10__cxxabiv121__vmi_class_type_infoE
+
+# This symbol is not an implementation detail of libc++abi, but it also causes issues when moving
+# to libc++. This needs further investigation.
+___cxa_rethrow_primary_exception
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index c1a7bcb14eb199..f95a8c471fd39f 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -214,14 +214,22 @@ if (LIBCXXABI_ENABLE_SHARED)
   endif()
 
   add_library(cxxabi-reexports INTERFACE)
-  function(reexport_symbols file)
+  function(export_symbols file)
     # -exported_symbols_list is only available on Apple platforms
     if (APPLE)
       target_link_libraries(cxxabi_shared PRIVATE "-Wl,-exported_symbols_list,${file}")
+    endif()
+  endfunction()
+
+  function(reexport_symbols file)
+    export_symbols("${file}")
+    # -reexported_symbols_list is only available on Apple platforms
+    if (APPLE)
       target_link_libraries(cxxabi-reexports INTERFACE "-Wl,-reexported_symbols_list,${file}")
     endif()
   endfunction()
 
+  export_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/symbols-not-reexported.exp")
   reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/cxxabiv1.exp")
   reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/fundamental-types.exp")
   reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/itanium-base.exp")

llvmbot · 2024-10-01T13:46:34Z

@llvm/pr-subscribers-libcxxabi

Author: None (llvmbot)

Changes

Backport 677e8cd

Requested by: @ldionne

Full diff: https://github.com/llvm/llvm-project/pull/110677.diff

7 Files Affected:

(modified) libcxx/lib/abi/CHANGELOG.TXT (+30)
(modified) libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist (-7)
(modified) libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist (-7)
(modified) libcxxabi/lib/cxxabiv1.exp (-3)
(modified) libcxxabi/lib/itanium-base.exp (-1)
(added) libcxxabi/lib/symbols-not-reexported.exp (+13)
(modified) libcxxabi/src/CMakeLists.txt (+9-1)

diff --git a/libcxx/lib/abi/CHANGELOG.TXT b/libcxx/lib/abi/CHANGELOG.TXT
index 32526f1786c6d9..68c9d980a016ea 100644
--- a/libcxx/lib/abi/CHANGELOG.TXT
+++ b/libcxx/lib/abi/CHANGELOG.TXT
@@ -16,6 +16,36 @@ New entries should be added directly below the "Version" header.
 Version 19.0
 ------------
 
+* [libc++] Avoid re-exporting a few specific symbols from libc++abi
+
+  In 6a884a9aef39, I synchronized the export list of libc++abi to the
+  export list of libc++. From the linker's perspective, this caused
+  these symbols to be taken from libc++.dylib instead of libc++abi.dylib.
+
+  However, that can be problematic when back-deploying. Indeed, this means
+  that the linker will encode an undefined reference to be fullfilled by
+  libc++.dylib, but when backdeploying against an older system, that symbol
+  might only be available in libc++abi.dylib.
+
+  Most of the symbols that started being re-exported after 6a884a9aef39
+  turn out to be implementation details of libc++abi, so nobody really
+  depends on them and this back-deployment issue is inconsequential.
+
+  However, we ran into issues with a few of these symbols while testing
+  LLVM 19, which led to this patch.
+
+  In the future, a follow-up cleanup would be to stop exporting most of
+  the _cxxabiv1_foo_type_infoE symbols from both libc++abi and libc++
+  since they are implementation details that nobody should be relying
+  on.
+
+  <arch>-apple-darwin
+  -------------------
+  Symbol not reexported anymore: ___cxa_rethrow_primary_exception
+  Symbol not reexported anymore: __ZTIN10__cxxabiv117__class_type_infoE
+  Symbol not reexported anymore: __ZTIN10__cxxabiv120__si_class_type_infoE
+  Symbol not reexported anymore: __ZTIN10__cxxabiv121__vmi_class_type_infoE
+
 * [libc++] Always keep libc++abi re-exports up-to-date
 
   This patch makes sure that the set of libc++abi symbols re-exported from libc++
diff --git a/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
index 917388f86811fe..32acae46e292d7 100644
--- a/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -78,12 +78,9 @@
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIPDh', 'type': 'U'}
@@ -2002,12 +1999,9 @@
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTINSt12experimental15fundamentals_v112bad_any_castE', 'size': 0, 'type': 'OBJECT'}
@@ -2615,7 +2609,6 @@
 {'is_defined': True, 'name': '___cxa_new_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_pure_virtual', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_rethrow', 'type': 'I'}
-{'is_defined': True, 'name': '___cxa_rethrow_primary_exception', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_terminate_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw_bad_array_new_length', 'type': 'I'}
diff --git a/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
index defe235a283c21..7b5d77499d55fa 100644
--- a/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -78,12 +78,9 @@
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'U'}
-{'is_defined': False, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'U'}
 {'is_defined': False, 'name': '__ZTIPDh', 'type': 'U'}
@@ -2002,12 +1999,9 @@
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__enum_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv116__shim_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__array_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv117__class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv117__pbase_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv119__pointer_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv120__function_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv120__si_class_type_infoE', 'type': 'I'}
-{'is_defined': True, 'name': '__ZTIN10__cxxabiv121__vmi_class_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv123__fundamental_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTIN10__cxxabiv129__pointer_to_member_type_infoE', 'type': 'I'}
 {'is_defined': True, 'name': '__ZTINSt12experimental15fundamentals_v112bad_any_castE', 'size': 0, 'type': 'OBJECT'}
@@ -2649,7 +2643,6 @@
 {'is_defined': True, 'name': '___cxa_new_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_pure_virtual', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_rethrow', 'type': 'I'}
-{'is_defined': True, 'name': '___cxa_rethrow_primary_exception', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_terminate_handler', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw', 'type': 'I'}
 {'is_defined': True, 'name': '___cxa_throw_bad_array_new_length', 'type': 'I'}
diff --git a/libcxxabi/lib/cxxabiv1.exp b/libcxxabi/lib/cxxabiv1.exp
index b1bab45ef33479..0a22831a63d0bb 100644
--- a/libcxxabi/lib/cxxabiv1.exp
+++ b/libcxxabi/lib/cxxabiv1.exp
@@ -2,12 +2,9 @@
 __ZTIN10__cxxabiv116__enum_type_infoE
 __ZTIN10__cxxabiv116__shim_type_infoE
 __ZTIN10__cxxabiv117__array_type_infoE
-__ZTIN10__cxxabiv117__class_type_infoE
 __ZTIN10__cxxabiv117__pbase_type_infoE
 __ZTIN10__cxxabiv119__pointer_type_infoE
 __ZTIN10__cxxabiv120__function_type_infoE
-__ZTIN10__cxxabiv120__si_class_type_infoE
-__ZTIN10__cxxabiv121__vmi_class_type_infoE
 __ZTIN10__cxxabiv123__fundamental_type_infoE
 __ZTIN10__cxxabiv129__pointer_to_member_type_infoE
 
diff --git a/libcxxabi/lib/itanium-base.exp b/libcxxabi/lib/itanium-base.exp
index 002e062df423e7..0c23a19c94c528 100644
--- a/libcxxabi/lib/itanium-base.exp
+++ b/libcxxabi/lib/itanium-base.exp
@@ -12,7 +12,6 @@ ___cxa_guard_acquire
 ___cxa_guard_release
 ___cxa_increment_exception_refcount
 ___cxa_pure_virtual
-___cxa_rethrow_primary_exception
 ___cxa_throw_bad_array_new_length
 ___cxa_uncaught_exception
 ___cxa_uncaught_exceptions
diff --git a/libcxxabi/lib/symbols-not-reexported.exp b/libcxxabi/lib/symbols-not-reexported.exp
new file mode 100644
index 00000000000000..ea5d0b3fc15d78
--- /dev/null
+++ b/libcxxabi/lib/symbols-not-reexported.exp
@@ -0,0 +1,13 @@
+# These symbols are not re-exported from libc++ because providing a definition in libc++ causes
+# issues with some clients when backdeploying.
+
+# These symbols are implementation details of libc++abi, but they are referenced from UBSan
+# (which is a total hack). We'll need to figure out how to decouple UBSan from these details
+# before we can stop exporting them from libc++abi.
+__ZTIN10__cxxabiv117__class_type_infoE
+__ZTIN10__cxxabiv120__si_class_type_infoE
+__ZTIN10__cxxabiv121__vmi_class_type_infoE
+
+# This symbol is not an implementation detail of libc++abi, but it also causes issues when moving
+# to libc++. This needs further investigation.
+___cxa_rethrow_primary_exception
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index c1a7bcb14eb199..f95a8c471fd39f 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -214,14 +214,22 @@ if (LIBCXXABI_ENABLE_SHARED)
   endif()
 
   add_library(cxxabi-reexports INTERFACE)
-  function(reexport_symbols file)
+  function(export_symbols file)
     # -exported_symbols_list is only available on Apple platforms
     if (APPLE)
       target_link_libraries(cxxabi_shared PRIVATE "-Wl,-exported_symbols_list,${file}")
+    endif()
+  endfunction()
+
+  function(reexport_symbols file)
+    export_symbols("${file}")
+    # -reexported_symbols_list is only available on Apple platforms
+    if (APPLE)
       target_link_libraries(cxxabi-reexports INTERFACE "-Wl,-reexported_symbols_list,${file}")
     endif()
   endfunction()
 
+  export_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/symbols-not-reexported.exp")
   reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/cxxabiv1.exp")
   reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/fundamental-types.exp")
   reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/itanium-base.exp")

ldionne · 2024-10-01T13:52:07Z

As I explained in the original PR, I think this is a fairly important fix since that was an unintentional change in LLVM 19, but this can also potentially break people who compiled with LLVM 19.1. Since we're making the fix on main, it will land in LLVM 20 anyway and I think it's best to land sooner rather than later, but I'll let the release manager decide.

@tru If you need additional context or information about this change, feel free to ping me on Discord and we could even set up a quick chat. I tried explaining the problem in detail in the ABI changelog (see the diff), but sometimes talking in person can be helpful.

var-const · 2024-10-10T17:11:53Z

@tru Thanks a lot for considering the patch! I just wanted to follow up to close the loop here -- would be awesome to either merge or close this patch, so that we can proceed with fixing our downstream issues according to the resolution. Thanks!

tru · 2024-10-11T05:46:36Z

I will merge this. I think we need to maybe have a note in the forums to announce this change.

tru · 2024-10-11T06:43:08Z

There are some CI failures - can someone check and confirm it's ok to merge anyway?

ldionne · 2024-10-11T14:45:31Z

I'm not seeing any CI failure anymore, I think this can be merged?

var-const · 2024-10-12T19:16:30Z

@tru Thank you so much for accepting this! It looks like the CI is clean now.

tru · 2024-10-15T06:49:59Z

Can someone post this as a breaking change to the discourse so that I can link it from the release notes?

…vm#109054) In 6a884a9, I synchronized the export list of libc++abi to the export list of libc++. From the linker's perspective, this caused these symbols to be taken from libc++.dylib instead of libc++abi.dylib. However, that can be problematic when back-deploying. Indeed, this means that the linker will encode an undefined reference to be fullfilled by libc++.dylib, but when backdeploying against an older system, that symbol might only be available in libc++abi.dylib. Most of the symbols that started being re-exported after 6a884a9 turn out to be implementation details of libc++abi, so nobody really depends on them and this back-deployment issue is inconsequential. However, we ran into issues with a few of these symbols while testing LLVM 19, which led to this patch. This slipped between the cracks and that is why the patch is coming so long after the original patch landed. In the future, a follow-up cleanup would be to stop exporting most of the _cxxabiv1_foo_type_infoE symbols from both libc++abi and libc++ since they are implementation details that nobody should be relying on. rdar://131984512 (cherry picked from commit 677e8cd)

github-actions · 2024-10-15T06:51:05Z

@ldionne (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.

ldionne · 2024-10-15T12:52:06Z

Can someone post this as a breaking change to the discourse so that I can link it from the release notes?

https://discourse.llvm.org/t/libc-llvm-19-1-2-removal-of-some-libc-abi-re-exported-symbols-on-apple-platforms/82551

(Still being moderated)

tru · 2024-10-15T14:14:29Z

Thanks, I have accepted it and linked it from the release post.

llvmbot requested review from a team as code owners October 1, 2024 13:45

llvmbot added this to the LLVM 19.X Release milestone Oct 1, 2024

llvmbot requested a review from var-const October 1, 2024 13:46

llvmbot mentioned this pull request Oct 1, 2024

[libc++] Avoid re-exporting a few specific symbols from libc++abi #109054

Merged

llvmbot added libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. libc++abi libc++abi C++ Runtime Library. Not libc++. labels Oct 1, 2024

tru force-pushed the issue109054 branch from c571c9a to 0faf262 Compare October 11, 2024 05:46

var-const approved these changes Oct 12, 2024

View reviewed changes

tru force-pushed the issue109054 branch from 0faf262 to c36d7fd Compare October 15, 2024 06:50

tru merged commit c36d7fd into llvm:release/19.x Oct 15, 2024
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release/19.x: [libc++] Avoid re-exporting a few specific symbols from libc++abi (#109054) #110677

release/19.x: [libc++] Avoid re-exporting a few specific symbols from libc++abi (#109054) #110677

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release/19.x: [libc++] Avoid re-exporting a few specific symbols from libc++abi (#109054) #110677

release/19.x: [libc++] Avoid re-exporting a few specific symbols from libc++abi (#109054) #110677

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