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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id c17-20020a0ce151000000b0062168714c8fsm1004048qvl.120.2023.06.02.09.56.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 02 Jun 2023 09:56:38 -0700 (PDT) Message-ID: <8b75c557-6b03-8456-dc6e-48f1969c7900@redhat.com> Date: Fri, 2 Jun 2023 12:56:37 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 Subject: PING Re: [PATCH RFA (tree-eh)] c++: use __cxa_call_terminate for MUST_NOT_THROW [PR97720] From: Jason Merrill To: gcc-patches@gcc.gnu.org Cc: libstdc++@gcc.gnu.org References: <20230524185559.1285583-1-jason@redhat.com> In-Reply-To: <20230524185559.1285583-1-jason@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.9 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,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: Since Jonathan approved the library change, I'm looking for middle-end approval for the tree-eh change, even without advice on the potential follow-up. On 5/24/23 14:55, Jason Merrill wrote: > 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