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 DE020396ECE8 for ; Fri, 8 May 2020 15:28:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org DE020396ECE8 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 A6AC1AB64; Fri, 8 May 2020 15:28:31 +0000 (UTC) Subject: Re: [PATCH][gdb] Fix stepping over fork with follow-fork-mode child and gcc-8 To: Simon Marchi , gdb-patches@sourceware.org Cc: Pedro Alves References: <20200507050409.GA30601@delia> <35196fcc-a6f4-c2ac-9cd5-70f5d0966cbe@simark.ca> From: Tom de Vries 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: <7e82416c-2fdb-785d-5068-a97310783948@suse.de> Date: Fri, 8 May 2020 17:28:28 +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: <35196fcc-a6f4-c2ac-9cd5-70f5d0966cbe@simark.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-14.5 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, KAM_NUMSUBJECT, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=no 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, 08 May 2020 15:28:31 -0000 On 08-05-2020 17:16, Simon Marchi wrote: > On 2020-05-07 1:04 a.m., Tom de Vries wrote: >> Hi, >> >> When running test-case gdb.threads/fork-child-threads.exp with gcc-8 instead >> of gcc-7, we have: >> ... >> (gdb) next^M >> [Attaching after Thread 0x7ffff7fae740 (LWP 27574) fork to child process \ >> 27578]^M >> [New inferior 2 (process 27578)]^M >> [Detaching after fork from parent process 27574]^M >> [Inferior 1 (process 27574) detached]^M >> [Thread debugging using libthread_db enabled]^M >> Using host libthread_db library "/lib64/libthread_db.so.1".^M >> [Switching to Thread 0x7ffff7fae740 (LWP 27578)]^M >> -main () at src/gdb/testsuite/gdb.threads/fork-child-threads.c:41^M >> +main () at src/gdb/testsuite/gdb.threads/fork-child-threads.c:34^M >> -41 i = pthread_create (&thread, NULL, start, NULL);^M >> +34 switch (fork ())^M >> -(gdb) PASS: gdb.threads/fork-child-threads.exp: next over fork >> +(gdb) FAIL: gdb.threads/fork-child-threads.exp: next over fork >> ... >> >> This is due to the fact that gcc-8 generates more precise line info, making >> the instruction after the call to fork a "recommended breakpoint location". >> However, it is a bug because next is supposed to move to the next source >> line. >> >> The problem is that in process_event_stop_test we hit this code: >> ... >> if ((ecs->event_thread->suspend.stop_pc == stop_pc_sal.pc) >> && (ecs->event_thread->current_line != stop_pc_sal.line >> || ecs->event_thread->current_symtab != stop_pc_sal.symtab)) >> { >> if (stop_pc_sal.is_stmt) >> { >> /* We are at the start of a different line. So stop. Note that >> we don't stop if we step into the middle of a different line. >> That is said to make things like for (;;) statements work >> better. */ >> if (debug_infrun) >> fprintf_unfiltered (gdb_stdlog, >> "infrun: stepped to a different line\n"); >> end_stepping_range (ecs); >> return; >> } >> ... >> because current_line and current_symtab have initial values: >> ... >> (gdb) p ecs->event_thread->current_line >> $8 = 0 >> (gdb) p ecs->event_thread->current_symtab >> $9 = (symtab *) 0x0 >> ... >> >> Fix this in follow_fork by copying current_line and current_symtab from >> parent thread to child thread. >> >> Tested on x86_64-linux, with gcc 7.5.0 and gcc 10.0.1. >> >> OK for trunk? > > Hi Tom, > > The change makes sense to me, although I don't know this code in depth (things > related to lines and SaL). But I confirm that it fixes on my machine the same > FAIL that you see. Thanks for the review, committed. - Tom