From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id S+3MIXa9/mAAWAAAWB0awg (envelope-from ) for ; Mon, 26 Jul 2021 09:49:42 -0400 Received: by simark.ca (Postfix, from userid 112) id 7AA151EDFB; Mon, 26 Jul 2021 09:49:42 -0400 (EDT) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=-0.7 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,RDNS_DYNAMIC,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (ip-8-43-85-97.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPS id 8C95E1E813 for ; Mon, 26 Jul 2021 09:49:41 -0400 (EDT) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id DE3323899003 for ; Mon, 26 Jul 2021 13:49:40 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org DE3323899003 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1627307380; bh=jo9Zq5sKUWn7fBFbnJ0D2lac/9ChB4kSlhrSUnTlx80=; h=Subject:To:References:Date:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=aYPH/zptSwVk5PIT2NvjDuFaCugaC2PDSXQuFHY/5aW3w17/YshrG9gZGSEOvOTGa NgZQs9tj1EXTansgjIc38XSdw3yI1d9fuemLCQDsY/ChkfLJZZV00jBGsP4KdVcmS+ XLPJMj69Ulnsag1OlxB9XSSmQEPFv0EF0Q46pv9w= Received: from smtp.polymtl.ca (smtp.polymtl.ca [132.207.4.11]) by sourceware.org (Postfix) with ESMTPS id 6F1AF385800D for ; Mon, 26 Jul 2021 13:49:19 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 6F1AF385800D Received: from simark.ca (simark.ca [158.69.221.121]) (authenticated bits=0) by smtp.polymtl.ca (8.14.7/8.14.7) with ESMTP id 16QDnDq2032105 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 26 Jul 2021 09:49:18 -0400 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp.polymtl.ca 16QDnDq2032105 Received: from [10.0.0.11] (192-222-157-6.qc.cable.ebox.net [192.222.157.6]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPSA id 5C5D11E813; Mon, 26 Jul 2021 09:49:13 -0400 (EDT) Subject: Re: [PATCH][gdb/symtab] Fix unhandled dwarf expression opcode with gcc-11 -gdwarf-5 To: Tom de Vries , gdb-patches@sourceware.org References: <20210725072237.GA31689@delia> Message-ID: Date: Mon, 26 Jul 2021 09:49:12 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210725072237.GA31689@delia> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Poly-FromMTA: (simark.ca [158.69.221.121]) at Mon, 26 Jul 2021 13:49:13 +0000 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: , From: Simon Marchi via Gdb-patches Reply-To: Simon Marchi Cc: Tom Tromey Errors-To: gdb-patches-bounces+public-inbox=simark.ca@sourceware.org Sender: "Gdb-patches" On 2021-07-25 3:22 a.m., Tom de Vries wrote: > Hi, > > [ I've confused things by forgetting to add -gdwarf-4 in $subject of > commit 0057a7ee0d9 "[gdb/testsuite] Add KFAILs for gdb.ada FAILs with > gcc-11". So I'm adding here -gdwarf-5 in $subject, even though -gdwarf-5 is > the default for gcc-11. I keep getting confused because of working with a > system gcc-11 compiler that was patched to switch the default back to > -gdwarf-4. ] > > When running test-case gdb.ada/arrayptr.exp with gcc-11 (and default > -gdwarf-5), I run into: > ... > (gdb) print pa_ptr.all^M > Unhandled dwarf expression opcode 0xff^M > (gdb) FAIL: gdb.ada/arrayptr.exp: scenario=all: print pa_ptr.all > ... > > What happens is that pa_ptr: > ... > <2><1523>: Abbrev Number: 3 (DW_TAG_variable) > <1524> DW_AT_name : pa_ptr > <1529> DW_AT_type : <0x14fa> > ... > has type: > ... > <2><14fa>: Abbrev Number: 2 (DW_TAG_typedef) > <14fb> DW_AT_name : foo__packed_array_ptr > <1500> DW_AT_type : <0x1504> > <2><1504>: Abbrev Number: 4 (DW_TAG_pointer_type) > <1505> DW_AT_byte_size : 8 > <1505> DW_AT_type : <0x1509> > ... > which is a pointer to a subrange: > ... > <2><1509>: Abbrev Number: 12 (DW_TAG_subrange_type) > <150a> DW_AT_lower_bound : 0 > <150b> DW_AT_upper_bound : 0x3fffffffffffffffff > <151b> DW_AT_name : foo__packed_array > <151f> DW_AT_type : <0x15cc> > <1523> DW_AT_artificial : 1 > <1><15cc>: Abbrev Number: 5 (DW_TAG_base_type) > <15cd> DW_AT_byte_size : 16 > <15ce> DW_AT_encoding : 7 (unsigned) > <15cf> DW_AT_name : long_long_long_unsigned > <15d3> DW_AT_artificial : 1 > ... > with upper bound of form DW_FORM_data16. > > In gdb/dwarf/attribute.h we have: > ... > /* Return non-zero if ATTR's value falls in the 'constant' class, or > zero otherwise. When this function returns true, you can apply > the constant_value method to it. > ... > DW_FORM_data16 is not considered as constant_value cannot handle > that. */ > bool form_is_constant () const; > ... > so instead we have attribute::form_is_block (DW_FORM_data16) == true. > > Then in attr_to_dynamic_prop for the upper bound, we get a PROC_LOCEXPR > instead of a PROP_CONST and end up trying to evaluate the constant > 0x3fffffffffffffffff as if it were a locexpr, which causes the > "Unhandled dwarf expression opcode 0xff". > > In contrast, with -gdwarf-4 we have: > ... > <164c> DW_AT_upper_bound : 18 byte block: \ > 9e 10 ff ff ff ff ff ff ff ff 3f 0 0 0 0 0 0 0 \ > (DW_OP_implicit_value 16 byte block: \ > ff ff ff ff ff ff ff ff 3f 0 0 0 0 0 0 0 ) > ... > > Fix the dwarf error by translating the DW_FORM_data16 constant into a > PROC_LOCEXPR, effectively by prepending 0x9e 0x10, such that we have same > result as with -gdwarf-4: Why is DW_FORM_data16 is handled as a block at the moment? It just looks wrong that DW_FORM_data16 is treated as a block and not a constant. It would be more logical to have this end up as a constant dynamic property, it would be more efficient than evaluating a location expression. Ah, but the const_val field is a LONGEST, we can't fit a 16 bytes number in there. But we can encode that value as a location expression, I see. However, this high bounds value stored as a location expression won't be very useful anyway. In most places (see get_discrete_high_bound), we just return 0 if the property is not constant. But we did evaluate it, the current interfaces that evaluate dynamic properties return CORE_ADDR or LONGEST, all 64-bit values, so we could not return that value. So if the property that you create was ever evaluated, it wouldn't yield a valid result anyway. I quickly tried to find a way to make GDB evaluate it to see what happens, but couldn't find one. If we ever want such a large high bound value to be useful, I think that some interfaces and some code would need to be converted to use arbitrary precision integers (using GMP maybe). And then dynamic_prop_data::const_val could be a GMP type instead of a LONGEST, allowing it to store that 16 bytes value. In which case we would probably undo your patch here, because, if we can store the 16-byte value as a constant directly, there's no need to convert it to a location expression. Simon