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 [216.205.24.124]) by sourceware.org (Postfix) with ESMTPS id 97BEE3858D3C for ; Mon, 8 Nov 2021 18:27:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 97BEE3858D3C Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-455-bnEFD5t9MlGPwbPQYDlHFA-1; Mon, 08 Nov 2021 13:27:46 -0500 X-MC-Unique: bnEFD5t9MlGPwbPQYDlHFA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F0C7B1023F4D for ; Mon, 8 Nov 2021 18:27:45 +0000 (UTC) Received: from blarsen.com (ovpn-116-73.gru2.redhat.com [10.97.116.73]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4637767848; Mon, 8 Nov 2021 18:27:43 +0000 (UTC) From: Bruno Larsen To: gdb-patches@sourceware.org Subject: [PATCH v2] PR gdb/28480: Improve ambiguous member detection Date: Mon, 8 Nov 2021 15:27:22 -0300 Message-Id: <20211108182722.29510-1-blarsen@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" X-Spam-Status: No, score=-13.5 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_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 08 Nov 2021 18:27:54 -0000 Basic ambiguity detection assumes that when 2 fields with the same name have the same boffset, it must be an unambiguous request. This is not always correct. Consider the following code: class empty { }; class A { public: [[no_unique_address]] empty e; }; class B { public: int e; }; class C: public A, public B { }; if we tried to use c.e in code, the compiler would warn of an ambiguity, however, since A::e does not demand an unique address, it gets the same address (and thus boffset) of the members, making A::e and B::e have the same address. however, "print c.e" would fail to report the ambiguity, and would instead print it as an empty class (first path found). The new code solves this by checking for other found_fields that have different m_struct_path.back() (final class that the member was found in), despite having the same boffset. The testcase gdb.cp/ambiguous.exp was also changed to test for this behavior. --- gdb/testsuite/gdb.cp/ambiguous.cc | 19 +++++++++++++++++++ gdb/testsuite/gdb.cp/ambiguous.exp | 10 ++++++++++ gdb/valops.c | 27 +++++++++++++++++++++++++++ 3 files changed, 56 insertions(+) diff --git a/gdb/testsuite/gdb.cp/ambiguous.cc b/gdb/testsuite/gdb.cp/ambiguous.cc index a55686547f2..af2198dcfbc 100644 --- a/gdb/testsuite/gdb.cp/ambiguous.cc +++ b/gdb/testsuite/gdb.cp/ambiguous.cc @@ -1,3 +1,4 @@ +class empty { }; class A1 { public: @@ -17,6 +18,17 @@ public: int y; }; +#if !defined (__GNUC__) || __GNUC__ > 7 +# define NO_UNIQUE_ADDRESS [[no_unique_address]] +#else +# define NO_UNIQUE_ADDRESS +#endif + +class A4 { +public: + NO_UNIQUE_ADDRESS empty x; +}; + class X : public A1, public A2 { public: int z; @@ -77,6 +89,10 @@ public: int jva1v; }; +class JE : public A1, public A4 { +public: +}; + int main() { A1 a1; @@ -92,6 +108,7 @@ int main() JVA1 jva1; JVA2 jva2; JVA1V jva1v; + JE je; int i; @@ -173,5 +190,7 @@ int main() jva1v.i = 4; jva1v.jva1v = 5; + je.A1::x = 1; + return 0; /* set breakpoint here */ } diff --git a/gdb/testsuite/gdb.cp/ambiguous.exp b/gdb/testsuite/gdb.cp/ambiguous.exp index 008898c5818..a2a7b02b113 100644 --- a/gdb/testsuite/gdb.cp/ambiguous.exp +++ b/gdb/testsuite/gdb.cp/ambiguous.exp @@ -264,3 +264,13 @@ gdb_test "print (A1)(KV)jva1" " = \{x = 3, y = 4\}" # JVA1V is derived from A1; A1 is a virtual base indirectly # and also directly; must not report ambiguity when a JVA1V is cast to an A1. gdb_test "print (A1)jva1v" " = {x = 1, y = 2}" + +# C++20 introduced a way to have ambiguous fields with the same boffset. +# This class explicitly tests for that. +# if this is tested with a compiler that can't handle [[no_unique_address]] +# the code should still correctly identify the ambiguity because of +# different boffsets. +test_ambiguous "je.x" "x" "JE" { + "'int A1::x' (JE -> A1)" + "'empty A4::x' (JE -> A4)" +} diff --git a/gdb/valops.c b/gdb/valops.c index 9787cdbb513..2989a93df1a 100644 --- a/gdb/valops.c +++ b/gdb/valops.c @@ -1962,6 +1962,33 @@ struct_field_searcher::update_result (struct value *v, LONGEST boffset) space. */ if (m_fields.empty () || m_last_boffset != boffset) m_fields.push_back ({m_struct_path, v}); + else + /* Some fields may occupy the same space and still be ambiguous. + This happens when [[no_unique_address]] is used by a member + of the class. We assume that this only happens when the types are + different. This is not necessarily complete, but a situation where + this assumption is incorrect is currently (2021) impossible. */ + { + bool ambiguous = false, insert = true; + for (const found_field& field: m_fields) { + if(field.path.back () != m_struct_path.back ()) + { + /* Same boffset points to members of different classes. + We have found an ambiguity and should record it. */ + ambiguous = true; + } + else + { + /* We don't need to insert this value again, because a + non-ambiguous path already leads to it. */ + insert = false; + break; + } + } + if (ambiguous && insert) { + m_fields.push_back ({m_struct_path, v}); + } + } } } } -- 2.27.0