Date: Sat, 13 Mar 2021 13:55:02 GMT From: Dimitry Andric <dim@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 0b45290603b9 - stable/13 - Partially revert libcxxrt changes to avoid _Unwind_Exception change Message-ID: <202103131355.12DDt2s6065316@gitrepo.freebsd.org>
next in thread | raw e-mail | index | archive | help
The branch stable/13 has been updated by dim: URL: https://cgit.FreeBSD.org/src/commit/?id=0b45290603b9d294dc2fbbf6d7b8fa20acd60175 commit 0b45290603b9d294dc2fbbf6d7b8fa20acd60175 Author: Dimitry Andric <dim@FreeBSD.org> AuthorDate: 2021-03-13 13:54:05 +0000 Commit: Dimitry Andric <dim@FreeBSD.org> CommitDate: 2021-03-13 13:54:05 +0000 Partially revert libcxxrt changes to avoid _Unwind_Exception change (Note I am also applying this to main and stable/13, to restore the old libcxxrt ABI and to avoid having to maintain a compat library.) After the recent cherry-picking of libcxxrt commits 0ee0dbfb0d26 and d2b3fadf2db5, users reported that editors/libreoffice packages from the official package builders did not start anymore. It turns out that the combination of these commits subtly changes the ABI, requiring all applications that depend on internal details of struct _Unwind_Exception (available via unwind-arm.h and unwind-itanium.h) to be recompiled. However, the FreeBSD package builders always use -RELEASE jails, so these still use the old declaration of struct _Unwind_Exception, which is not entirely compatible. In particular, LibreOffice uses this struct in its internal "uno bridge" component, where it attempts to setup its own exception handling mechanism. To fix this incompatibility, go back to the old declarations of struct _Unwind_Exception, and restore the __LP64__ specific workaround we had in place before (which was to cope with yet another, older ABI bug). Effectively, this reverts upstream libcxxrt commits 88bdf6b290da ("Specify double-word alignment for ARM unwind") and b96169641f79 ("Updated Itanium unwind"), and reapplies our commit 3c4fd2463bb2 ("libcxxrt: add padding in __cxa_allocate_* to fix alignment"). PR: 253840 --- contrib/libcxxrt/exception.cc | 30 ++++++++++++++++++++++++------ contrib/libcxxrt/unwind-arm.h | 2 +- contrib/libcxxrt/unwind-itanium.h | 9 +++------ 3 files changed, 28 insertions(+), 13 deletions(-) diff --git a/contrib/libcxxrt/exception.cc b/contrib/libcxxrt/exception.cc index 0fb26ddb4ed2..0de878e9e6db 100644 --- a/contrib/libcxxrt/exception.cc +++ b/contrib/libcxxrt/exception.cc @@ -572,6 +572,19 @@ static void free_exception(char *e) } } +#ifdef __LP64__ +/** + * There's an ABI bug in __cxa_exception: unwindHeader requires 16-byte + * alignment but it was broken by the addition of the referenceCount. + * The unwindHeader is at offset 0x58 in __cxa_exception. In order to keep + * compatibility with consumers of the broken __cxa_exception, explicitly add + * padding on allocation (and account for it on free). + */ +static const int exception_alignment_padding = 8; +#else +static const int exception_alignment_padding = 0; +#endif + /** * Allocates an exception structure. Returns a pointer to the space that can * be used to store an object of thrown_size bytes. This function will use an @@ -580,16 +593,19 @@ static void free_exception(char *e) */ extern "C" void *__cxa_allocate_exception(size_t thrown_size) { - size_t size = thrown_size + sizeof(__cxa_exception); + size_t size = exception_alignment_padding + sizeof(__cxa_exception) + + thrown_size; char *buffer = alloc_or_die(size); - return buffer+sizeof(__cxa_exception); + return buffer + exception_alignment_padding + sizeof(__cxa_exception); } extern "C" void *__cxa_allocate_dependent_exception(void) { - size_t size = sizeof(__cxa_dependent_exception); + size_t size = exception_alignment_padding + + sizeof(__cxa_dependent_exception); char *buffer = alloc_or_die(size); - return buffer+sizeof(__cxa_dependent_exception); + return buffer + exception_alignment_padding + + sizeof(__cxa_dependent_exception); } /** @@ -617,7 +633,8 @@ extern "C" void __cxa_free_exception(void *thrown_exception) } } - free_exception(reinterpret_cast<char*>(ex)); + free_exception(reinterpret_cast<char*>(ex) - + exception_alignment_padding); } static void releaseException(__cxa_exception *exception) @@ -644,7 +661,8 @@ void __cxa_free_dependent_exception(void *thrown_exception) { releaseException(realExceptionFromException(reinterpret_cast<__cxa_exception*>(ex))); } - free_exception(reinterpret_cast<char*>(ex)); + free_exception(reinterpret_cast<char*>(ex) - + exception_alignment_padding); } /** diff --git a/contrib/libcxxrt/unwind-arm.h b/contrib/libcxxrt/unwind-arm.h index ec81237e573b..6eb9d9e45981 100644 --- a/contrib/libcxxrt/unwind-arm.h +++ b/contrib/libcxxrt/unwind-arm.h @@ -97,7 +97,7 @@ struct _Unwind_Exception } pr_cache; /** Force alignment of next item to 8-byte boundary */ long long int :0; -} __attribute__((__aligned__(8))); +}; /* Unwinding functions */ _Unwind_Reason_Code _Unwind_RaiseException(struct _Unwind_Exception *ucbp); diff --git a/contrib/libcxxrt/unwind-itanium.h b/contrib/libcxxrt/unwind-itanium.h index 199d91de283d..1ee0cf0e81c4 100644 --- a/contrib/libcxxrt/unwind-itanium.h +++ b/contrib/libcxxrt/unwind-itanium.h @@ -79,12 +79,9 @@ struct _Unwind_Exception { uint64_t exception_class; _Unwind_Exception_Cleanup_Fn exception_cleanup; - uintptr_t private_1; - uintptr_t private_2; -#if __SIZEOF_POINTER__ == 4 - uint32_t reserved[3]; -#endif - } __attribute__((__aligned__)); + unsigned long private_1; + unsigned long private_2; + } ; extern _Unwind_Reason_Code _Unwind_RaiseException (struct _Unwind_Exception *); extern _Unwind_Reason_Code _Unwind_ForcedUnwind (struct _Unwind_Exception *,
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?202103131355.12DDt2s6065316>