Author: ahatanak Date: Tue May 16 10:19:08 2017 New Revision: 303175 URL: http://llvm.org/viewvc/llvm-project?rev=303175&view=rev Log: [libcxxabi] Align unwindHeader on a double-word boundary.
r276215 made a change to annotate _Unwind_Exception with attribute "aligned" so that an exception object following field __cxa_exception is sufficiently aligned. This fix hasn't been incorporated to unwind.h on Darwin since it is an ABI breaking change. Instead of annotating struct _Unwind_Exception with the attribute, this commit annotates field unwindHeader of __cxa_exception. This ensures the exception object is sufficiently aligned without breaking the ABI. This recommits r302978 and r302981, which were reverted in r303016 because a libcxx test was failing on an AArch64 bot. I also modified the libcxxabi test case to check the alignment of the pointer returned by __cxa_allocate_exception rather than compiling the test with -O1 and checking whether it segfaults. rdar://problem/25364625 Differential Revision: https://reviews.llvm.org/D33030 Added: libcxxabi/trunk/test/exception_object_alignment.pass.cpp Modified: libcxxabi/trunk/src/cxa_exception.hpp Modified: libcxxabi/trunk/src/cxa_exception.hpp URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/src/cxa_exception.hpp?rev=303175&r1=303174&r2=303175&view=diff ============================================================================== --- libcxxabi/trunk/src/cxa_exception.hpp (original) +++ libcxxabi/trunk/src/cxa_exception.hpp Tue May 16 10:19:08 2017 @@ -61,7 +61,21 @@ struct _LIBCXXABI_HIDDEN __cxa_exception size_t referenceCount; #endif + // This field is annotated with attribute aligned so that the exception + // object following the field is sufficiently aligned and there is no + // gap between the field and the exception object. r276215 made a change to + // annotate _Unwind_Exception in unwind.h with __attribute__((aligned)), but + // we cannot incorporate the fix on Darwin since it is an ABI-breaking + // change, which is why we need the attribute on this field. + // + // For ARM EHABI, we do not align this field since _Unwind_Exception is an + // alias of _Unwind_Control_Block, which is not annotated with + // __attribute__((aligned). +#if defined(_LIBCXXABI_ARM_EHABI) _Unwind_Exception unwindHeader; +#else + _Unwind_Exception unwindHeader __attribute__((aligned)); +#endif }; // http://sourcery.mentor.com/archives/cxx-abi-dev/msg01924.html @@ -96,7 +110,13 @@ struct _LIBCXXABI_HIDDEN __cxa_dependent void* primaryException; #endif + // See the comment in __cxa_exception as to why this field has attribute + // aligned. +#if defined(_LIBCXXABI_ARM_EHABI) _Unwind_Exception unwindHeader; +#else + _Unwind_Exception unwindHeader __attribute__((aligned)); +#endif }; struct _LIBCXXABI_HIDDEN __cxa_eh_globals { Added: libcxxabi/trunk/test/exception_object_alignment.pass.cpp URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/exception_object_alignment.pass.cpp?rev=303175&view=auto ============================================================================== --- libcxxabi/trunk/test/exception_object_alignment.pass.cpp (added) +++ libcxxabi/trunk/test/exception_object_alignment.pass.cpp Tue May 16 10:19:08 2017 @@ -0,0 +1,33 @@ +//===---------------- exception_object_alignment.pass.cpp -----------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is dual licensed under the MIT and the University of Illinois Open +// Source Licenses. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +// UNSUPPORTED: libcxxabi-no-exceptions + +// Check that the pointer __cxa_allocate_exception returns is aligned to the +// default alignment for the target architecture. + +#include <cassert> +#include <cstdint> +#include <cxxabi.h> +#include <type_traits> +#include <__cxxabi_config.h> + +struct S { + int a[4]; +} __attribute__((aligned)); + +int main() { +#if !defined(_LIBCXXABI_ARM_EHABI) + void *p = __cxxabiv1::__cxa_allocate_exception(16); + auto i = reinterpret_cast<uintptr_t>(p); + auto a = std::alignment_of<S>::value; + assert(i % a == 0); +#endif + return 0; +} _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
