From 2415024e0f81f8c09bf08f947c790b43de9d0bbc Mon Sep 17 00:00:00 2001 From: Jason Merrill Date: Tue, 23 May 2023 12:25:15 -0400 Subject: c++: use __cxa_call_terminate for MUST_NOT_THROW [PR97720] [except.handle]/7 says that when we enter std::terminate due to a throw, that is considered an active handler. We already implemented that properly for the case of not finding a handler (__cxa_throw calls __cxa_begin_catch before std::terminate) and the case of finding a callsite with no landing pad (the personality function calls __cxa_call_terminate which calls __cxa_begin_catch), but for the case of a throw in a try/catch in a noexcept function, we were emitting a cleanup that calls std::terminate directly without ever calling __cxa_begin_catch to handle the exception. A straightforward way to fix this seems to be calling __cxa_call_terminate instead. However, that requires exporting it from libstdc++, which we have not previously done. Despite the name, it isn't actually part of the ABI standard. Nor is __cxa_call_unexpected, as far as I can tell, but that one is also used by clang. For this case they use __clang_call_terminate; it seems reasonable to me for us to stick with __cxa_call_terminate. I also change __cxa_call_terminate to take void* for simplicity in the front end (and consistency with __cxa_call_unexpected) but that isn't necessary if it's undesirable for some reason. This patch does not fix the issue that representing the noexcept as a cleanup is wrong, and confuses the handler search; since it looks like a cleanup in the EH tables, the unwinder keeps looking until it finds the catch in main(), which it should never have gotten to. Without the try/catch in main, the unwinder would reach the end of the stack and say no handler was found. The noexcept is a handler, and should be treated as one, as it is when the landing pad is omitted. The best fix for that issue seems to me to be to represent an ERT_MUST_NOT_THROW after an ERT_TRY in an action list as though it were an ERT_ALLOWED_EXCEPTIONS (since indeed it is an exception-specification). The actual code generation shouldn't need to change (apart from the change made by this patch), only the action table entry. PR c++/97720 gcc/cp/ChangeLog: * cp-tree.h (enum cp_tree_index): Add CPTI_CALL_TERMINATE_FN. (call_terminate_fn): New macro. * cp-gimplify.cc (gimplify_must_not_throw_expr): Use it. * except.cc (init_exception_processing): Set it. (cp_protect_cleanup_actions): Return it. gcc/ChangeLog: * tree-eh.cc (lower_resx): Pass the exception pointer to the failure_decl. * except.h: Tweak comment. libstdc++-v3/ChangeLog: * libsupc++/eh_call.cc (__cxa_call_terminate): Take void*. * config/abi/pre/gnu.ver: Add it. gcc/testsuite/ChangeLog: * g++.dg/eh/terminate2.C: New test. --- gcc/except.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'gcc/except.h') diff --git a/gcc/except.h b/gcc/except.h index 5ecdbc0..378a9e4 100644 --- a/gcc/except.h +++ b/gcc/except.h @@ -155,7 +155,7 @@ struct GTY(()) eh_region_d struct eh_region_u_must_not_throw { /* A function decl to be invoked if this region is actually reachable from within the function, rather than implementable from the runtime. - The normal way for this to happen is for there to be a CLEANUP region + The normal way for this to happen is for there to be a TRY region contained within this MUST_NOT_THROW region. Note that if the runtime handles the MUST_NOT_THROW region, we have no control over what termination function is called; it will be decided by the -- cgit v1.1