From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.145.221.124]) by sourceware.org (Postfix) with ESMTPS id 431543858CDB for ; Fri, 26 May 2023 09:59:15 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 431543858CDB Authentication-Results: sourceware.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=fail smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685095154; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8+hDD/TJW3/iCdnAy5K8AJ1ery1BPc3U6Q1gbgOlgy4=; b=QObzcbVdy6/Wo1OzLgbmEw676mj7Kasf7debkgk+nPdtElrar1mPPhKs5ht3TENDdXFUWE gFWjVIDsz3DM/5X5aVImKOKG3TyBCDx6lNsINySuqaEOKnVF4McH/Js8ts2agI4qZb7ji8 PGnd+fxX/XSFpetPKMLvJtYkFWSayKc= Received: from mail-lf1-f72.google.com (mail-lf1-f72.google.com [209.85.167.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-2-r6J7BJBBP9iJpKhHBj1Evg-1; Fri, 26 May 2023 05:59:12 -0400 X-MC-Unique: r6J7BJBBP9iJpKhHBj1Evg-1 Received: by mail-lf1-f72.google.com with SMTP id 2adb3069b0e04-4edc7406cbaso283694e87.2 for ; Fri, 26 May 2023 02:59:12 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685095151; x=1687687151; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=8+hDD/TJW3/iCdnAy5K8AJ1ery1BPc3U6Q1gbgOlgy4=; b=FpCsSi+7X61eZ3x0i1uJYtIysZ4p15meYsPUr3RjKZmlwPVbkaWZjmfAg+BzbDoqP4 ltxUkZLVN+TwJbUcp9vLSnXkmvex86hj7F+kTFRE4EfCpALi9dAc0Z0m1uOrFV5cPjza HcRfQB+1Z0lrO0lAawOzt8qbTHxjiWMZ5iGn6fUOO0XJYYzS6ikaMobnRM4WlET4VGnp pcb6BhjJm7EDYsJFJ9Ct2XopyfwduGzuEmwNYcP+8w1hRdVKdARm3AmftaWsRzkl1LWp oEeHzU2/ofcdqaCK5IznyFTjUqm16U6OfL+yCeExw+7+wxDCZOlbWL2/vDwt48WvMbc+ h/kg== X-Gm-Message-State: AC+VfDyQoTX47YoGpmpENK7kv+aLiNof18aNZvFq6uTp4x7+jtVT2mJW QRQlyeZ2lSnsQGg+PVVJl2OHvwneCy6vslMd0wk1Hh0AwuIePlp7Rzn0GlMWkDblSdfM3ZBFdlA e/3VpGprW9O1ODWtJ4OZFKUL3H0NPyvnij79PM00VUg== X-Received: by 2002:a19:c513:0:b0:4f1:2180:5683 with SMTP id w19-20020a19c513000000b004f121805683mr348553lfe.41.1685095151369; Fri, 26 May 2023 02:59:11 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ7IKiD4tSNszFtjd1o+0uuDvGQCHrjvou0pdLRZvYmXitdsiueK5S2SDCmCqTRiYKvkn1gKypHdC4CPp4k6eqk= X-Received: by 2002:a19:c513:0:b0:4f1:2180:5683 with SMTP id w19-20020a19c513000000b004f121805683mr348548lfe.41.1685095151031; Fri, 26 May 2023 02:59:11 -0700 (PDT) MIME-Version: 1.0 References: <20230524185559.1285583-1-jason@redhat.com> In-Reply-To: <20230524185559.1285583-1-jason@redhat.com> From: Jonathan Wakely Date: Fri, 26 May 2023 10:58:59 +0100 Message-ID: Subject: Re: [PATCH RFC] c++: use __cxa_call_terminate for MUST_NOT_THROW [PR97720] To: Jason Merrill Cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/alternative; boundary="000000000000e3f3ae05fc95c94e" X-Spam-Status: No, score=-12.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,HTML_MESSAGE,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: --000000000000e3f3ae05fc95c94e Content-Type: text/plain; charset="UTF-8" On Wed, 24 May 2023 at 19:56, Jason Merrill via Libstdc++ < libstdc++@gcc.gnu.org> 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? > I see no harm in exporting it (with the adjusted signature). The "looks standard but isn't" name is a little unfortunate, but not a big deal. > > -- 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 > > --000000000000e3f3ae05fc95c94e--