From patchwork Fri Nov 21 14:53:47 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Patrick Palka X-Patchwork-Id: 3833 Received: (qmail 18165 invoked by alias); 21 Nov 2014 14:53:57 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Delivered-To: mailing list gdb-patches@sourceware.org Received: (qmail 18145 invoked by uid 89); 21 Nov 2014 14:53:55 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.4 required=5.0 tests=AWL, BAYES_00, RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.2 X-HELO: mail-qa0-f45.google.com Received: from mail-qa0-f45.google.com (HELO mail-qa0-f45.google.com) (209.85.216.45) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-SHA encrypted) ESMTPS; Fri, 21 Nov 2014 14:53:53 +0000 Received: by mail-qa0-f45.google.com with SMTP id x12so3511487qac.32 for ; Fri, 21 Nov 2014 06:53:51 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:date:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; bh=/i4GbTADHsl6ZR2D53BvtgHVHXd02VpmlMDi5LKlm6Q=; b=beVrxF7ZZyiPGFiTpS7FL6Kn+KpofIaobncYt5dmY/nEZ11vj+WImPpxflTMG/t0xW 9xk6SVIeOu3jzNZtE0beFhA1hGedeJQUgNzHyZHctTQ4TC6PSbA0LFeuYMPLT7yZSSqa 3DxWzwm7JDs+GbHFPluI00wtR4R8IcQzOxha66H6Asvga5hyAfLVBbloTxk4JBT7LeOp fQpnTOOwZUlCuIpXClmV0rZ5pVVTUj5KrQQstxcZRKM8RIEkfI7KsDslInOXtfiZjTXi tNHZtvSdl+kplfKYGqBNWlSMd3YM6DNWDlSuraYq1P4fjEY/kXyZ3ZKr3Ja3FAN9jfzf 1aKw== X-Gm-Message-State: ALoCoQmFnslR72UhqklahNj8p9iXKZIwXuvq7xFLVnFcA2WT1WZqXrLynbAgl0BwURb1sxg2ayUO X-Received: by 10.140.42.135 with SMTP id c7mr6817216qga.7.1416581631499; Fri, 21 Nov 2014 06:53:51 -0800 (PST) Received: from [192.168.1.130] (ool-4353af5c.dyn.optonline.net. [67.83.175.92]) by mx.google.com with ESMTPSA id r4sm4828546qan.31.2014.11.21.06.53.49 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 21 Nov 2014 06:53:50 -0800 (PST) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Fri, 21 Nov 2014 09:53:47 -0500 (EST) To: Yao Qi cc: Patrick Palka , gdb-patches@sourceware.org Subject: Re: [PATCH 1/2] Fix C++ virtual method pointer resolution In-Reply-To: <87389cfze2.fsf@codesourcery.com> Message-ID: References: <1411355243-10812-1-git-send-email-patrick@parcs.ath.cx> <87k32og51t.fsf@codesourcery.com> <87389cfze2.fsf@codesourcery.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 X-IsSubscribed: yes On Fri, 21 Nov 2014, Yao Qi wrote: > Patrick Palka writes: > >>>> +get_debug_format >>>> + >>>> +if ![test_debug_format "DWARF 2"] { >>>> + return 0 >>>> +} >>> >>> Why do we need to check test_debug_format here? >> >> Because GDB only supports C++ method pointers with the DWARF debug >> format. So I'd assume that this test would fail for non-DWARF. > > I am not aware of this, any details? If GDB doesn't support C++ method > pointers with non-DWARF, we should kfail or xfail it in the test. See > gdb.cp/m-static.exp. > > -- > Yao (齐尧) > Here's an updated version of the patch which removes the test_debug_format check and also shifts vtable offset on !vbit_in_delta architectures. Of course, the internal GDB encoding may still be inconsistent with the ABI but at least it is self-consistent now. -- >8 -- Subject: [PATCH] Fix C++ virtual method pointer resolution C++ virtual method pointer resolution is currently broken, in that a virtual method pointer will sometimes resolve to the wrong symbol. A minimal testcase is the following program: struct x { virtual void f (); virtual void g (); } void x::f () { } void x::g () { } (gdb) print &x::f $1 = &virtual x::f() (gdb) print &x::g $1 = &virtual x::f() As you can see, &x::f correctly resolves to x::f(), but &x::g incorrectly resolves to x::f() instead of x::g(). The issue lies in the initial creation of the virtual method pointer as seen by GDB. In gnuv3_make_method_ptr() we fail to shift the vtable offset when storing the first word of a virtual method pointer. This is important because functions that read this first word (namely the callers of gnuv3_decode_method_ptr()) expect that the vtable offset is a multiple of "sizeof (vtable_ptrdiff_t)". Also it ensures that the vbit tag does not collide with the bits used to store the actual offset. So when writing the virtual method pointer contents we need to shift the vtable offset so as to be in symmetry with what the readers of the vtable offset do -- which is, xor the vbit tag and then shift back the offset. (The prominent readers of the vtable offset are gnuv3_print_method_ptr() and gnuv3_method_ptr_to_value().) gdb/ChangeLog * gnu-v3-abi.c (gnuv3_make_method_ptr): Shift the vtable offset. gdb/testsuite/ChangeLog * gdb.cp/method-ptr.exp: New test. * gdb.cp/method-ptr.cc: New testcase. Tested on x86_64-unknown-linux-gnu. --- gdb/gnu-v3-abi.c | 9 +++++- gdb/testsuite/gdb.cp/method-ptr.cc | 58 +++++++++++++++++++++++++++++++++++++ gdb/testsuite/gdb.cp/method-ptr.exp | 54 ++++++++++++++++++++++++++++++++++ 3 files changed, 120 insertions(+), 1 deletion(-) create mode 100644 gdb/testsuite/gdb.cp/method-ptr.cc create mode 100644 gdb/testsuite/gdb.cp/method-ptr.exp diff --git a/gdb/gnu-v3-abi.c b/gdb/gnu-v3-abi.c index d673e77..5775d85 100644 --- a/gdb/gnu-v3-abi.c +++ b/gdb/gnu-v3-abi.c @@ -682,11 +682,18 @@ gnuv3_make_method_ptr (struct type *type, gdb_byte *contents, if (!gdbarch_vbit_in_delta (gdbarch)) { - store_unsigned_integer (contents, size, byte_order, value | is_virtual); + if (is_virtual != 0) + { + value = value * TYPE_LENGTH (vtable_ptrdiff_type (gdbarch)); + value = value | 1; + } + store_unsigned_integer (contents, size, byte_order, value); store_unsigned_integer (contents + size, size, byte_order, 0); } else { + if (is_virtual != 0) + value = value * TYPE_LENGTH (vtable_ptrdiff_type (gdbarch)); store_unsigned_integer (contents, size, byte_order, value); store_unsigned_integer (contents + size, size, byte_order, is_virtual); } diff --git a/gdb/testsuite/gdb.cp/method-ptr.cc b/gdb/testsuite/gdb.cp/method-ptr.cc new file mode 100644 index 0000000..db47484 --- /dev/null +++ b/gdb/testsuite/gdb.cp/method-ptr.cc @@ -0,0 +1,58 @@ +/* This testcase is part of GDB, the GNU debugger. + + Copyright 2014 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 . */ + +struct x +{ + virtual void f (); + virtual void g (); + virtual void h (); +}; + +void x::f () { } +void x::g () { } +void x::h () { } + +struct y : x +{ + virtual void f (); + + virtual void j (); + virtual void k (); +}; + +void y::f () { } +void y::j () { } +void y::k () { } + +struct z : y +{ + virtual void g (); + virtual void j (); + + virtual void l (); + virtual void m (); +}; + +void z::g () { } +void z::j () { } +void z::l () { } +void z::m () { } + +int +main () +{ +} diff --git a/gdb/testsuite/gdb.cp/method-ptr.exp b/gdb/testsuite/gdb.cp/method-ptr.exp new file mode 100644 index 0000000..cd3d8ff --- /dev/null +++ b/gdb/testsuite/gdb.cp/method-ptr.exp @@ -0,0 +1,54 @@ +# Copyright 2014 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 . + +# This file is part of the gdb testsuite + +if [skip_cplus_tests] { continue } + +standard_testfile .cc + +if [prepare_for_testing $testfile.exp $testfile $srcfile {debug c++}] { + return -1 +} + +if ![runto_main] { + return -1 +} + +# Check that the virtual method pointer NAME resolves to symbol SYMBOL. +proc check_virtual_method_ptr_resolution { name symbol } { + global decimal + + # Printing the expression &NAME should show the resolved symbol SYMBOL. + gdb_test "print &$name" "\\$$decimal = &virtual $symbol\\(\\)\\s" +} + +check_virtual_method_ptr_resolution "x::f" "x::f" +check_virtual_method_ptr_resolution "x::g" "x::g" +check_virtual_method_ptr_resolution "x::h" "x::h" + +check_virtual_method_ptr_resolution "y::f" "y::f" +check_virtual_method_ptr_resolution "y::g" "x::g" +check_virtual_method_ptr_resolution "y::h" "x::h" +check_virtual_method_ptr_resolution "y::j" "y::j" +check_virtual_method_ptr_resolution "y::k" "y::k" + +check_virtual_method_ptr_resolution "z::f" "y::f" +check_virtual_method_ptr_resolution "z::g" "z::g" +check_virtual_method_ptr_resolution "z::h" "x::h" +check_virtual_method_ptr_resolution "z::j" "z::j" +check_virtual_method_ptr_resolution "z::k" "y::k" +check_virtual_method_ptr_resolution "z::l" "z::l" +check_virtual_method_ptr_resolution "z::m" "z::m"