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From 986bd28388df745dd969e7be7c3bda36b2b2cb0e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Caol=C3=A1n=20McNamara?= <caolanm@redhat.com>
Date: Thu, 6 Aug 2020 10:50:47 +0100
Subject: [PATCH] ofz#24641 libc++abi __cxa_exception has grown another member
MIME-Version: 1.0
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https: //github.com/llvm/llvm-project/commit/f2a436058fcbc11291e73badb44e243f61046183
this is the same problem as
commit f4b6f6a8ae60bdec53512728d00853b73fa18500
Author: Stephan Bergmann <sbergman@redhat.com>
Date: Thu Feb 13 08:40:11 2020 +0100
Hack to dynamically adapt to __cxa_exceptiom in LLVM 11 libcxxabi
(where the new change to __cxa_exception effectively reverts the change that
prompted 7a9dd3d482deeeb3ed1d50074e56adbd3f928296 "Hack to dynamically adapt to
__cxa_exceptiom in LLVM 5.0 libcxxabi")
Change-Id: Iec4ef1dc188bea2223d99b1b7eb8adec636c98e7
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/88583
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
so c-n-p that solution here
Change-Id: I4475757a766e3ade7b9fcaf6149e535c9f9a4fa4
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100209
Tested-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
---
.../cpp_uno/gcc3_linux_x86-64/except.cxx | 28 +++++++++++++++++++
.../cpp_uno/gcc3_linux_x86-64/share.hxx | 14 ++++++++++
2 files changed, 42 insertions(+)
diff --git a/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx b/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx
index e9e861f1c210..25931671f7dc 100644
--- a/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx
+++ b/bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx
@@ -150,6 +150,34 @@ void fillUnoException(uno_Any * pUnoExc, uno_Mapping * pCpp2Uno)
return;
}
+#if defined _LIBCPPABI_VERSION // detect libc++abi
+ // Very bad HACK to find out whether we run against a libcxxabi that has a new
+ // __cxa_exception::reserved member at the start, introduced with LLVM 11
+ // <https://github.com/llvm/llvm-project/commit/f2a436058fcbc11291e73badb44e243f61046183>
+ // "[libcxxabi] Insert padding in __cxa_exception struct for compatibility". The layout of the
+ // start of __cxa_exception is
+ //
+ // [8 byte void *reserve]
+ // 8 byte size_t referenceCount
+ //
+ // where the (bad, hacky) assumption is that reserve (if present) is null
+ // (__cxa_allocate_exception in at least LLVM 11 zero-fills the object, and nothing actively
+ // sets reserve) while referenceCount is non-null (__cxa_throw sets it to 1, and
+ // __cxa_decrement_exception_refcount destroys the exception as soon as it drops to 0; for a
+ // __cxa_dependent_exception, the referenceCount member is rather
+ //
+ // 8 byte void* primaryException
+ //
+ // but which also will always be set to a non-null value in __cxa_rethrow_primary_exception).
+ // As described in the definition of __cxa_exception
+ // (bridges/source/cpp_uno/gcc3_linux_x86-64/share.hxx), this hack (together with the "#if 0"
+ // there) can be dropped once we can be sure that we only run against new libcxxabi that has the
+ // reserve member:
+ if (*reinterpret_cast<void **>(header) == nullptr) {
+ header = reinterpret_cast<__cxxabiv1::__cxa_exception*>(reinterpret_cast<void **>(header) + 1);
+ }
+#endif
+
std::type_info *exceptionType = __cxxabiv1::__cxa_current_exception_type();
typelib_TypeDescription * pExcTypeDescr = nullptr;
diff --git a/bridges/source/cpp_uno/gcc3_linux_x86-64/share.hxx b/bridges/source/cpp_uno/gcc3_linux_x86-64/share.hxx
index e8afe35c4f59..53c8841fbbcb 100644
--- a/bridges/source/cpp_uno/gcc3_linux_x86-64/share.hxx
+++ b/bridges/source/cpp_uno/gcc3_linux_x86-64/share.hxx
@@ -108,6 +108,20 @@ namespace __cxxabiv1 {
struct __cxa_exception {
#if defined _LIBCPPABI_VERSION // detect libc++abi
#if defined __LP64__ || LIBCXXABI_ARM_EHABI
+#if 0
+ // This is a new field added with LLVM 11
+ // <https://github.com/llvm/llvm-project/commit/f2a436058fcbc11291e73badb44e243f61046183>
+ // "[libcxxabi] Insert padding in __cxa_exception struct for compatibility". The HACK in
+ // fillUnoException (bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx) tries to find out at
+ // runtime whether a __cxa_exception has this member. Once we can be sure that we only run
+ // against new libcxxabi that has this member, we can drop the "#if 0" here and drop the hack
+ // in fillUnoException.
+
+ // Now _Unwind_Exception is marked with __attribute__((aligned)),
+ // which implies __cxa_exception is also aligned. Insert padding
+ // in the beginning of the struct, rather than before unwindHeader.
+ void *reserve;
+#endif
std::size_t referenceCount;
#endif
#endif
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