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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id dz18-20020ad45892000000b00623819de804sm3759889qvb.127.2023.05.24.11.56.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 May 2023 11:56:01 -0700 (PDT) From: Jason Merrill To: gcc-patches@gcc.gnu.org Cc: libstdc++@gcc.gnu.org Subject: [PATCH RFC] c++: use __cxa_call_terminate for MUST_NOT_THROW [PR97720] Date: Wed, 24 May 2023 14:55:59 -0400 Message-Id: <20230524185559.1285583-1-jason@redhat.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII"; x-default=true X-Spam-Status: No, score=-12.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Middle-end folks: any thoughts about how best to make the change described in the last paragraph below? Library folks: any thoughts on the changes to __cxa_call_terminate? -- 8< -- [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-tree.h | 2 ++ gcc/except.h | 2 +- gcc/cp/cp-gimplify.cc | 2 +- gcc/cp/except.cc | 5 ++++- gcc/testsuite/g++.dg/eh/terminate2.C | 30 ++++++++++++++++++++++++++++ gcc/tree-eh.cc | 16 ++++++++++++++- libstdc++-v3/libsupc++/eh_call.cc | 4 +++- libstdc++-v3/config/abi/pre/gnu.ver | 7 +++++++ 8 files changed, 63 insertions(+), 5 deletions(-) create mode 100644 gcc/testsuite/g++.dg/eh/terminate2.C diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index a1b882f11fe..a8465a988b5 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/except.h b/gcc/except.h index 5ecdbc0d1dc..378a9e4cb77 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 diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc index 216a6231d6f..853b1e44236 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/except.cc b/gcc/cp/except.cc index 91a5e049860..b04eb00d220 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 diff --git a/gcc/testsuite/g++.dg/eh/terminate2.C b/gcc/testsuite/g++.dg/eh/terminate2.C new file mode 100644 index 00000000000..1c69dab95f8 --- /dev/null +++ b/gcc/testsuite/g++.dg/eh/terminate2.C @@ -0,0 +1,30 @@ +// PR c++/97720 +// { dg-do run } + +// Test that there is an active exception when we reach the terminate handler. + +#include +#include + +void bad_guy() throw() { + try { throw 0; } + catch (float) { } + // Don't catch int. +} + +void level1() { + bad_guy(); + throw "dead code"; +} + +void my_term() +{ + try { throw; } + catch(...) { std::exit(0); } +} + +int main() { + std::set_terminate (my_term); + try { level1(); } + catch (int) { } +} diff --git a/gcc/tree-eh.cc b/gcc/tree-eh.cc index 934209d205f..e8ceff36cc6 100644 --- a/gcc/tree-eh.cc +++ b/gcc/tree-eh.cc @@ -3382,8 +3382,22 @@ lower_resx (basic_block bb, gresx *stmt, lab = gimple_block_label (new_bb); gsi2 = gsi_start_bb (new_bb); + /* Handle failure fns that expect either no arguments or the + exception pointer. */ fn = dst_r->u.must_not_throw.failure_decl; - x = gimple_build_call (fn, 0); + if (TYPE_ARG_TYPES (TREE_TYPE (fn)) != void_list_node) + { + tree epfn = builtin_decl_implicit (BUILT_IN_EH_POINTER); + src_nr = build_int_cst (integer_type_node, src_r->index); + x = gimple_build_call (epfn, 1, src_nr); + tree var = create_tmp_var (ptr_type_node); + var = make_ssa_name (var, x); + gimple_call_set_lhs (x, var); + gsi_insert_after (&gsi2, x, GSI_CONTINUE_LINKING); + x = gimple_build_call (fn, 1, var); + } + else + x = gimple_build_call (fn, 0); gimple_set_location (x, dst_r->u.must_not_throw.failure_loc); gsi_insert_after (&gsi2, x, GSI_CONTINUE_LINKING); diff --git a/libstdc++-v3/libsupc++/eh_call.cc b/libstdc++-v3/libsupc++/eh_call.cc index 3cfc71a4ef1..2bec4e83a7d 100644 --- a/libstdc++-v3/libsupc++/eh_call.cc +++ b/libstdc++-v3/libsupc++/eh_call.cc @@ -36,8 +36,10 @@ using namespace __cxxabiv1; // terminate. extern "C" void -__cxa_call_terminate(_Unwind_Exception* ue_header) throw () +__cxa_call_terminate(void* ue_header_in) throw () { + _Unwind_Exception* ue_header + = reinterpret_cast<_Unwind_Exception*>(ue_header_in); if (ue_header) { diff --git a/libstdc++-v3/config/abi/pre/gnu.ver b/libstdc++-v3/config/abi/pre/gnu.ver index 768cd4a4a6c..a2e5f3b4e74 100644 --- a/libstdc++-v3/config/abi/pre/gnu.ver +++ b/libstdc++-v3/config/abi/pre/gnu.ver @@ -2841,6 +2841,13 @@ CXXABI_1.3.14 { } CXXABI_1.3.13; +CXXABI_1.3.15 { + + global: + __cxa_call_terminate; + +} CXXABI_1.3.14; + # Symbols in the support library (libsupc++) supporting transactional memory. CXXABI_TM_1 { base-commit: 2738955004256c2e9753364d78a7be340323b74b -- 2.31.1