From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by sourceware.org (Postfix) with ESMTPS id DBE45383E817 for ; Fri, 5 Jun 2020 16:00:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org DBE45383E817 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tdevries@suse.de X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 58C9EAD07; Fri, 5 Jun 2020 16:00:51 +0000 (UTC) Subject: Re: [PATCH 2/3] gdb: Don't reorder line table entries too much when sorting. From: Tom de Vries To: Andrew Burgess , gdb-patches@sourceware.org References: <51b43dba-2213-a428-d4dd-10154f8d1f52@suse.de> Autocrypt: addr=tdevries@suse.de; keydata= xsBNBF0ltCcBCADDhsUnMMdEXiHFfqJdXeRvgqSEUxLCy/pHek88ALuFnPTICTwkf4g7uSR7 HvOFUoUyu8oP5mNb4VZHy3Xy8KRZGaQuaOHNhZAT1xaVo6kxjswUi3vYgGJhFMiLuIHdApoc u5f7UbV+egYVxmkvVLSqsVD4pUgHeSoAcIlm3blZ1sDKviJCwaHxDQkVmSsGXImaAU+ViJ5l CwkvyiiIifWD2SoOuFexZyZ7RUddLosgsO0npVUYbl6dEMq2a5ijGF6/rBs1m3nAoIgpXk6P TCKlSWVW6OCneTaKM5C387972qREtiArTakRQIpvDJuiR2soGfdeJ6igGA1FZjU+IsM5ABEB AAHNH1RvbSBkZSBWcmllcyA8dGRldnJpZXNAc3VzZS5kZT7CwKsEEwEIAD4WIQSsnSe5hKbL MK1mGmjuhV2rbOJEoAUCXSW0JwIbAwUJA8JnAAULCQgHAgYVCgkICwIEFgIDAQIeAQIXgAAh CRDuhV2rbOJEoBYhBKydJ7mEpsswrWYaaO6FXats4kSgc48H/Ra2lq5p3dHsrlQLqM7N68Fo eRDf3PMevXyMlrCYDGLVncQwMw3O/AkousktXKQ42DPJh65zoXB22yUt8m0g12xkLax98KFJ 5NyUloa6HflLl+wQL/uZjIdNUQaHQLw3HKwRMVi4l0/Jh/TygYG1Dtm8I4o708JS4y8GQxoQ UL0z1OM9hyM3gI2WVTTyprsBHy2EjMOu/2Xpod95pF8f90zBLajy6qXEnxlcsqreMaqmkzKn 3KTZpWRxNAS/IH3FbGQ+3RpWkNGSJpwfEMVCeyK5a1n7yt1podd1ajY5mA1jcaUmGppqx827 8TqyteNe1B/pbiUt2L/WhnTgW1NC1QDOwE0EXSW0JwEIAM99H34Bu4MKM7HDJVt864MXbx7B 1M93wVlpJ7Uq+XDFD0A0hIal028j+h6jA6bhzWto4RUfDl/9mn1StngNVFovvwtfzbamp6+W pKHZm9X5YvlIwCx131kTxCNDcF+/adRW4n8CU3pZWYmNVqhMUiPLxElA6QhXTtVBh1RkjCZQ Kmbd1szvcOfaD8s+tJABJzNZsmO2hVuFwkDrRN8Jgrh92a+yHQPd9+RybW2l7sJv26nkUH5Z 5s84P6894ebgimcprJdAkjJTgprl1nhgvptU5M9Uv85Pferoh2groQEAtRPlCGrZ2/2qVNe9 XJfSYbiyedvApWcJs5DOByTaKkcAEQEAAcLAkwQYAQgAJhYhBKydJ7mEpsswrWYaaO6FXats 4kSgBQJdJbQnAhsMBQkDwmcAACEJEO6FXats4kSgFiEErJ0nuYSmyzCtZhpo7oVdq2ziRKD3 twf7BAQBZ8TqR812zKAD7biOnWIJ0McV72PFBxmLIHp24UVe0ZogtYMxSWKLg3csh0yLVwc7 H3vldzJ9AoK3Qxp0Q6K/rDOeUy3HMqewQGcqrsRRh0NXDIQk5CgSrZslPe47qIbe3O7ik/MC q31FNIAQJPmKXX25B115MMzkSKlv4udfx7KdyxHrTSkwWZArLQiEZj5KG4cCKhIoMygPTA3U yGaIvI/BGOtHZ7bEBVUCFDFfOWJ26IOCoPnSVUvKPEOH9dv+sNy7jyBsP5QxeTqwxC/1ZtNS DUCSFQjqA6bEGwM22dP8OUY6SC94x1G81A9/xbtm9LQxKm0EiDH8KBMLfQ== Message-ID: <446082ca-c3d4-1a90-2a35-2669c8407095@suse.de> Date: Fri, 5 Jun 2020 18:00:40 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <51b43dba-2213-a428-d4dd-10154f8d1f52@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-16.3 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) 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: Fri, 05 Jun 2020 16:00:50 -0000 On 05-06-2020 16:49, Tom de Vries wrote: > On 23-12-2019 02:51, Andrew Burgess wrote: >> I had to make a small adjustment in find_pc_sect_line in order to >> correctly find the previous line in the line table. In some line >> tables I was seeing an actual line entry and an end of sequence marker >> at the same address, before this commit these would reorder to move >> the end of sequence marker before the line entry (end of sequence has >> line number 0). Now the end of sequence marker remains in its correct >> location, and in order to find a previous line we should step backward >> over any end of sequence markers. >> >> As an example, the binary: >> gdb/testsuite/outputs/gdb.dwarf2/dw2-ranges-func/dw2-ranges-func-lo-cold >> >> Has this line table before the patch: >> >> INDEX LINE ADDRESS >> 0 48 0x0000000000400487 >> 1 END 0x000000000040048e >> 2 52 0x000000000040048e >> 3 54 0x0000000000400492 >> 4 56 0x0000000000400497 >> 5 END 0x000000000040049a >> 6 62 0x000000000040049a >> 7 END 0x00000000004004a1 >> 8 66 0x00000000004004a1 >> 9 68 0x00000000004004a5 >> 10 70 0x00000000004004aa >> 11 72 0x00000000004004b9 >> 12 END 0x00000000004004bc >> 13 76 0x00000000004004bc >> 14 78 0x00000000004004c0 >> 15 80 0x00000000004004c5 >> 16 END 0x00000000004004cc >> >> And after this patch: >> >> INDEX LINE ADDRESS >> 0 48 0x0000000000400487 >> 1 52 0x000000000040048e >> 2 END 0x000000000040048e >> 3 54 0x0000000000400492 >> 4 56 0x0000000000400497 >> 5 END 0x000000000040049a >> 6 62 0x000000000040049a >> 7 66 0x00000000004004a1 >> 8 END 0x00000000004004a1 >> 9 68 0x00000000004004a5 >> 10 70 0x00000000004004aa >> 11 72 0x00000000004004b9 >> 12 END 0x00000000004004bc >> 13 76 0x00000000004004bc >> 14 78 0x00000000004004c0 >> 15 80 0x00000000004004c5 >> 16 END 0x00000000004004cc >> >> When calling find_pc_sect_line with the address 0x000000000040048e, in >> both cases we find entry #3, we then try to find the previous entry, >> which originally found this entry '2 52 0x000000000040048e', >> after the patch it finds '2 END 0x000000000040048e', which >> cases the lookup to fail. >> >> By skipping the END marker after this patch we get back to the correct >> entry, which is now #1: '1 52 0x000000000040048e', and >> everything works again. > > I start to suspect that you have been working around an incorrect line > table. > > Consider this bit: > ... > 0 48 0x0000000000400487 > 1 52 0x000000000040048e > 2 END 0x000000000040048e > ... > > The end marker marks the address one past the end of the sequence. > Therefore, it makes no sense to have an entry in the sequence with the > same address as the end marker. > > [ dwarf doc: > > end_sequence: > > A boolean indicating that the current address is that of the first byte > after the end of a sequence of target machine instructions. end_sequence > terminates a sequence of lines; therefore other information in the same > row is not meaningful. > > DW_LNE_end_sequence: > > The DW_LNE_end_sequence opcode takes no operands. It sets the > end_sequence register of the state machine to “true” and appends a row > to the matrix using the current values of the state-machine registers. > Then it resets the registers to the initial values specified above (see > Section 6.2.2). Every line number program sequence must end with a > DW_LNE_end_sequence instruction which creates a row whose address is > that of the byte after the last target machine instruction of the sequence. > > ] > > The incorrect entry is generated by this dwarf assembler sequence: > ... > {DW_LNS_copy} > {DW_LNE_end_sequence} > ... > > I think we should probably fix the dwarf assembly test-cases. > > If we want to handle this in gdb, the thing that seems most logical to > me is to ignore this kind of entries. Hmm, that seems to be done already, in buildsym_compunit::record_line. Anyway, I was looking at the line table for gdb.dwarf2/dw2-ranges-base.exp, and got a line table with subsequent end markers: ... INDEX LINE ADDRESS IS-STMT 0 31 0x00000000004004a7 Y 1 21 0x00000000004004ae Y 2 END 0x00000000004004ae Y 3 11 0x00000000004004ba Y 4 END 0x00000000004004ba Y 5 END 0x00000000004004c6 Y ... By using this patch: ... diff --git a/gdb/buildsym.c b/gdb/buildsym.c index 33bf6523e9..76f0b54ff6 100644 --- a/gdb/buildsym.c +++ b/gdb/buildsym.c @@ -943,6 +943,10 @@ buildsym_compunit::end_symtab_with_blockvector (struct block *static_block, = [] (const linetable_entry &ln1, const linetable_entry &ln2) -> bool { + if (ln1.pc == ln2.pc + && ((ln1.line == 0) != (ln2.line == 0))) + return ln1.line == 0 ? true : false; + return (ln1.pc < ln2.pc); }; ... I get the expected: ... INDEX LINE ADDRESS IS-STMT 0 31 0x00000000004004a7 Y 1 END 0x00000000004004ae Y 2 21 0x00000000004004ae Y 3 END 0x00000000004004ba Y 4 11 0x00000000004004ba Y 5 END 0x00000000004004c6 Y ... Thanks, - Tom