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/cp/cp-gimplify.cc | 2 +- gcc/cp/cp-tree.h | 2 ++ gcc/cp/except.cc | 5 ++++- 3 files changed, 7 insertions(+), 2 deletions(-) (limited to 'gcc/cp') diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc index 216a623..853b1e4 100644 --- a/gcc/cp/cp-gimplify.cc +++ b/gcc/cp/cp-gimplify.cc @@ -343,7 +343,7 @@ gimplify_must_not_throw_expr (tree *expr_p, gimple_seq *pre_p) gimple *mnt; gimplify_and_add (body, &try_); - mnt = gimple_build_eh_must_not_throw (terminate_fn); + mnt = gimple_build_eh_must_not_throw (call_terminate_fn); gimple_seq_add_stmt_without_update (&catch_, mnt); mnt = gimple_build_try (try_, catch_, GIMPLE_TRY_CATCH); diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index ce2095c..101da35 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -217,6 +217,7 @@ enum cp_tree_index definitions. */ CPTI_ALIGN_TYPE, CPTI_TERMINATE_FN, + CPTI_CALL_TERMINATE_FN, CPTI_CALL_UNEXPECTED_FN, /* These are lazily inited. */ @@ -358,6 +359,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX]; /* Exception handling function declarations. */ #define terminate_fn cp_global_trees[CPTI_TERMINATE_FN] #define call_unexpected_fn cp_global_trees[CPTI_CALL_UNEXPECTED_FN] +#define call_terminate_fn cp_global_trees[CPTI_CALL_TERMINATE_FN] #define get_exception_ptr_fn cp_global_trees[CPTI_GET_EXCEPTION_PTR_FN] #define begin_catch_fn cp_global_trees[CPTI_BEGIN_CATCH_FN] #define end_catch_fn cp_global_trees[CPTI_END_CATCH_FN] diff --git a/gcc/cp/except.cc b/gcc/cp/except.cc index 91a5e04..b04eb00 100644 --- a/gcc/cp/except.cc +++ b/gcc/cp/except.cc @@ -64,6 +64,9 @@ init_exception_processing (void) tmp = build_function_type_list (void_type_node, ptr_type_node, NULL_TREE); call_unexpected_fn = push_throw_library_fn (get_identifier ("__cxa_call_unexpected"), tmp); + call_terminate_fn + = push_library_fn (get_identifier ("__cxa_call_terminate"), tmp, NULL_TREE, + ECF_NORETURN | ECF_COLD | ECF_NOTHROW); } /* Returns an expression to be executed if an unhandled exception is @@ -76,7 +79,7 @@ cp_protect_cleanup_actions (void) When the destruction of an object during stack unwinding exits using an exception ... void terminate(); is called. */ - return terminate_fn; + return call_terminate_fn; } static tree -- cgit v1.1