From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 42169 invoked by alias); 24 Oct 2017 10:59:22 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 41587 invoked by uid 89); 24 Oct 2017 10:59:21 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: =?ISO-8859-1?Q?No, score=-21.4 required=5.0 tests=BAYES_00,FREEMAIL_FROM,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,HTML_MESSAGE,RCVD_IN_DNSWL_NONE,RCVD_IN_SORBS_SPAM,SPF_PASS autolearn=ham version=3.3.2 spammy=H*c:alternative, UD:c=c2?= X-HELO: mail-yw0-f172.google.com Received: from mail-yw0-f172.google.com (HELO mail-yw0-f172.google.com) (209.85.161.172) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 24 Oct 2017 10:59:19 +0000 Received: by mail-yw0-f172.google.com with SMTP id j4so14661255ywb.2 for ; Tue, 24 Oct 2017 03:59:19 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to; bh=VMxIMavX5Qa/O5zkDrJW3ytCa7Z1xV7ekr7vTrAMYdQ=; b=n/JO2/iH8Kn0mV7zRz8DD7lL0YE4eHDra3fIZwCeWms1lACn101SIb3EK6CEaChm7y TjIPOz7yGopfah3+OrzUawRHvxKUBDRrpEvE1Ar+Fy3pjAMvoxbyEuLdBHVF1AGL7ja3 5Xt8kzElUuURAqH59iV5mJpZIhZt1LoEHTSnfpULPhtDUEbLIzIUOIE1XZnfSN+9E82e j+0ki51mJl+2N5bykcCrO63V8in/28uKhS1vPB90EzHAAvAl55HeD34cpDtnpxEkeIjl 2bE/yhzqJMOTLVmNgQiAJQAO/QCT3i67Wk+vOozMxMQ222jaqUm7psm3qDM/Yi6MqbBb 4EkA== X-Gm-Message-State: AMCzsaXryoNRqUByOmV8hblCHJzUg2zU0nyll8ZYbKN5wLGHTeo9ahfs hfPqm82feLmoh8qNKZPtt/fXn37Y5MfihKIvtxakulH/ X-Google-Smtp-Source: ABhQp+R8UFCLMcrOMIcKnbcn+QJYmGqmBbqbKTMibfLh5Y2l+FuwIuTWKvZKUdn2MJ9WBRE8Jbuk+iCLKn10FMoXPpY= X-Received: by 10.129.148.130 with SMTP id l124mr10971706ywg.3.1508842757428; Tue, 24 Oct 2017 03:59:17 -0700 (PDT) MIME-Version: 1.0 Received: by 10.37.162.205 with HTTP; Tue, 24 Oct 2017 03:59:17 -0700 (PDT) In-Reply-To: <20171024105535.13287-1-osscontribute@gmail.com> References: <20171024105535.13287-1-osscontribute@gmail.com> From: Patrick Frants Date: Tue, 24 Oct 2017 10:59:00 -0000 Message-ID: Subject: Re: [PATCH] Fix broken recursion detection when printing static members To: gdb-patches@sourceware.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-SW-Source: 2017-10/txt/msg00743.txt.bz2 I am so sorry, looks like git send-email removed the first N lines. Here is the complete changelog: Fix broken recursion detection when printing static members Recursion detection for static members was broken. The implementation uses a growing (and shrinking) obstack object to simulate a stack of addresses (CORE_ADDR). Pushing addresses is implemented by calling obstack_grow(), while popping is implemented by calling obstack_free(). The latter is problematic because obstack_free() expects a pointer to the base of an object. When popping elements of the stack however, obstack_free() was called with the new top, which potentially is not the same as the base of the stack. This is unintended use and the effect is that obstack->next_free and obstack->object_base members are assigned the value of the new top, which equals an empty stack. Summary: popping elements would always result in an empty stack, which breaks the recursion detection. The fix shrinks the stack using obstack_blank_fast() with a negative value as described at the bottom of this page: https://gcc.gnu.org/onlinedocs/libiberty/Extra-Fast-Growing.html "You can use obstack_blank_fast with a =E2=80=9Cnegative=E2=80=9D size argu= ment to make the current object smaller. Just don=E2=80=99t try to shrink it beyond zero length=E2=80=94there=E2=80=99s no telling what will happen if you do that. = Earlier versions of obstacks allowed you to use obstack_blank to shrink objects. This will no longer work." A unit test (gdb.cp/printstaticrecursion.exp) was added. No new regression has been observed in testsuite/gdb.cp/*.exp. On Tue, Oct 24, 2017 at 12:55 PM, Patrick Frants wrote: > The fix shrinks the stack using obstack_blank_fast() with a negative value > as described at the bottom of this page: https://gcc.gnu.org/ > onlinedocs/libiberty/Extra-Fast-Growing.html > "You can use obstack_blank_fast with a =E2=80=9Cnegative=E2=80=9D size ar= gument to make > the current object smaller. Just don=E2=80=99t try to shrink it beyond ze= ro > length=E2=80=94there=E2=80=99s no telling what will happen if you do that= . Earlier versions > of obstacks allowed you to use obstack_blank to shrink objects. This will > no longer work." > > A unit test (gdb.cp/printstaticrecursion.exp) was added. No new > regression has been observed in testsuite/gdb.cp/*.exp. > --- > gdb/cp-valprint.c | 9 ++----- > gdb/testsuite/gdb.cp/printstaticrecursion.cc | 18 +++++++++++++ > gdb/testsuite/gdb.cp/printstaticrecursion.exp | 37 > +++++++++++++++++++++++++++ > 3 files changed, 57 insertions(+), 7 deletions(-) > create mode 100644 gdb/testsuite/gdb.cp/printstaticrecursion.cc > create mode 100644 gdb/testsuite/gdb.cp/printstaticrecursion.exp > > diff --git a/gdb/cp-valprint.c b/gdb/cp-valprint.c > index fb9bfd904f..927273f8a2 100644 > --- a/gdb/cp-valprint.c > +++ b/gdb/cp-valprint.c > @@ -371,13 +371,8 @@ cp_print_value_fields (struct type *type, struct type > *real_type, > if (obstack_final_size > statmem_obstack_initial_size) > { > /* In effect, a pop of the printed-statics stack. */ > - > - void *free_to_ptr =3D > - (char *) obstack_next_free (&dont_print_statmem_obstack) - > - (obstack_final_size - statmem_obstack_initial_size); > - > - obstack_free (&dont_print_statmem_obstack, > - free_to_ptr); > + size_t shrink_bytes =3D statmem_obstack_initial_size - > obstack_final_size; > + obstack_blank_fast (&dont_print_statmem_obstack, > shrink_bytes); > } > > if (last_set_recurse !=3D recurse) > diff --git a/gdb/testsuite/gdb.cp/printstaticrecursion.cc > b/gdb/testsuite/gdb.cp/printstaticrecursion.cc > new file mode 100644 > index 0000000000..40fd3c0c27 > --- /dev/null > +++ b/gdb/testsuite/gdb.cp/printstaticrecursion.cc > @@ -0,0 +1,18 @@ > +struct Inner > +{ > + static Inner instance; > +}; > + > +struct Outer > +{ > + Inner inner; > + static Outer instance; > +}; > + > +Inner Inner::instance; > +Outer Outer::instance; > + > +int main() > +{ > + return 0; /* break-here */ > +} > \ No newline at end of file > diff --git a/gdb/testsuite/gdb.cp/printstaticrecursion.exp > b/gdb/testsuite/gdb.cp/printstaticrecursion.exp > new file mode 100644 > index 0000000000..a71adc7d03 > --- /dev/null > +++ b/gdb/testsuite/gdb.cp/printstaticrecursion.exp > @@ -0,0 +1,37 @@ > +# Copyright 2008-2017 Free Software Foundation, Inc. > + > +# This program is free software; you can redistribute it and/or modify > +# it under the terms of the GNU General Public License as published by > +# the Free Software Foundation; either version 3 of the License, or > +# (at your option) any later version. > +# > +# This program is distributed in the hope that it will be useful, > +# but WITHOUT ANY WARRANTY; without even the implied warranty of > +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > +# GNU General Public License for more details. > +# > +# You should have received a copy of the GNU General Public License > +# along with this program. If not, see . > + > + > +if { [skip_cplus_tests] } { continue } > + > +standard_testfile printstaticrecursion.cc > + > +# Create and source the file that provides information about the compiler > +# used to compile the test case. > +if [get_compiler_info "c++"] { > + untested "couldn't find a valid c++ compiler" > + return -1 > +} > + > +if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug > c++}]} { > + return -1 > +} > + > +if ![runto_main] then { > + perror "couldn't run to main" > + continue > +} > + > +gdb_test "print Outer::instance" "{inner =3D {static instance =3D {static > instance =3D }}, static > instance =3D {inner =3D {static instance =3D {static instance =3D member of an already seen type>}}, static instance =3D of an already seen type>}}" "print recursive static member" > -- > 2.14.0 > >