From 986bd28388df745dd969e7be7c3bda36b2b2cb0e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Caol=C3=A1n=20McNamara?= 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit https: //github.com/llvm/llvm-project/commit/f2a436058fcbc11291e73badb44e243f61046183 this is the same problem as commit f4b6f6a8ae60bdec53512728d00853b73fa18500 Author: Stephan Bergmann 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 so c-n-p that solution here Change-Id: I4475757a766e3ade7b9fcaf6149e535c9f9a4fa4 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100209 Tested-by: Caolán McNamara Reviewed-by: Caolán McNamara --- .../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 + // + // "[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(header) == nullptr) { + header = reinterpret_cast<__cxxabiv1::__cxa_exception*>(reinterpret_cast(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 + // + // "[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