From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 2699 invoked by alias); 16 Nov 2014 03:57:19 -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 2687 invoked by uid 89); 16 Nov 2014 03:57:18 -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-pa0-f44.google.com Received: from mail-pa0-f44.google.com (HELO mail-pa0-f44.google.com) (209.85.220.44) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-SHA encrypted) ESMTPS; Sun, 16 Nov 2014 03:57:16 +0000 Received: by mail-pa0-f44.google.com with SMTP id et14so5249494pad.17 for ; Sat, 15 Nov 2014 19:57:14 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; bh=nDjTPJehoPBwvxeJBFfGxbf4JU0AZPORXHpSzzecYqY=; b=VeZy5w7LawkaE45hjRHlmGgcKaY3BdLOjMXCZEhi9fj3/EJr+xrXr3ap01PNcgVJlY jpWxDvl5HZUVV76c8ZJRMK3Kxs2+UkgqHTGk/moqf/E+doC4rV5HPVyoW7fIBtxX8vFb PECiDqozRtpc4j2rjhL0SlW7k3fWAiHKREqLX0Cl2X/2TpjUheRsM1qc9GkT+QPXtNO6 gUuyYUQ287M8zPnGVnoK3mYZe20laEx5biNBk6U4enotOiij1j5Lmke+vq8+FuBebomo y77VqJEP7kQHtDRNF/dEfJ+JMfHMYmEL/V7Y5XGty5WE9tk0dx+AMY2yTHVxOkqj55CS wlCA== X-Gm-Message-State: ALoCoQnjYTRduMgL66+tOkxxZ4i0PlUDarkJ9Vv4UBR+qs+DAfdnCFhq54NXKjXAJUTp20YxmgwA X-Received: by 10.68.217.197 with SMTP id pa5mr7310561pbc.32.1416110234291; Sat, 15 Nov 2014 19:57:14 -0800 (PST) MIME-Version: 1.0 Received: by 10.70.31.100 with HTTP; Sat, 15 Nov 2014 19:56:53 -0800 (PST) In-Reply-To: References: <1411355243-10812-1-git-send-email-patrick@parcs.ath.cx> From: Patrick Palka Date: Sun, 16 Nov 2014 03:57:00 -0000 Message-ID: Subject: Re: [PATCH 1/2] Fix C++ virtual method pointer resolution To: gdb-patches@sourceware.org Cc: Patrick Palka Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes X-SW-Source: 2014-11/txt/msg00372.txt.bz2 On Tue, Sep 30, 2014 at 5:48 PM, Patrick Palka wrote: > On Sun, Sep 21, 2014 at 11:07 PM, Patrick Palka wrote: >> 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 >> before setting the virtual bit. >> >> 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 | 7 ++++- >> gdb/testsuite/gdb.cp/method-ptr.cc | 58 +++++++++++++++++++++++++++++++++++ >> gdb/testsuite/gdb.cp/method-ptr.exp | 60 +++++++++++++++++++++++++++++++++++++ >> 3 files changed, 124 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 d5ed355..ccb0be6 100644 >> --- a/gdb/gnu-v3-abi.c >> +++ b/gdb/gnu-v3-abi.c >> @@ -683,7 +683,12 @@ 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 >> 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..732b861 >> --- /dev/null >> +++ b/gdb/testsuite/gdb.cp/method-ptr.exp >> @@ -0,0 +1,60 @@ >> +# 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 $srcfile {debug c++}] { >> + return -1 >> +} >> + >> +if ![runto_main] { >> + return -1 >> +} >> + >> +get_debug_format >> + >> +if ![test_debug_format "DWARF 2"] { >> + return 0 >> +} >> + >> +# Check that the virtual method pointer NAME resolves to symbol SYMBOL. >> +proc check_virtual_method_ptr_resolution { name symbol } { >> + global decimal >> + >> + # Printing the expression &NAME should show the resolved symbol SYMBOL. >> + gdb_test "print &$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" >> -- >> 2.1.1.273.g97b8860 >> > > Ping. Ping.