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 8EA2B38708B8 for ; Thu, 3 Sep 2020 10:34:52 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 8EA2B38708B8 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 [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9BBC5AB89; Thu, 3 Sep 2020 10:34:52 +0000 (UTC) Subject: [committed][PATCH][gdb/breakpoint, PIE] Handle setting breakpoint on label without address From: Tom de Vries To: Pedro Alves , gdb-patches@sourceware.org References: <20200827115217.GA17450@delia.home> <23b43acc-9846-a03c-5207-3ae80efc1d6f@palves.net> <29930a75-5de9-43ed-6a24-2909eb70ec66@suse.de> <79ab7968-bd35-aa3a-dd8b-37076609043d@suse.de> <205b09a4-d0d9-bf96-1c4b-fbe60dcde45c@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: <1fa82998-cd08-cd2c-cc92-92ef31c6b73a@suse.de> Date: Thu, 3 Sep 2020 12:34:49 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <205b09a4-d0d9-bf96-1c4b-fbe60dcde45c@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-10.2 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, KAM_STOCKGEN, 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: Thu, 03 Sep 2020 10:34:54 -0000 On 8/28/20 3:20 PM, Tom de Vries wrote: > [ was: Re: [PATCH][gdb/breakpoint] Handle setting breakpoint on label > without address ] > > On 8/28/20 12:31 PM, Tom de Vries wrote: >> On 8/27/20 3:49 PM, Tom de Vries wrote: >>> On 8/27/20 2:41 PM, Pedro Alves wrote: >>>> On 8/27/20 12:52 PM, Tom de Vries wrote: >>>>> Hi, >>>>> >>>>> Consider test-case test.c: >>>>> ... >>>>> $ cat test.c >>>>> int main (void) { >>>>> return 0; >>>>> L1: >>>>> (void)0; >>>>> } >>>>> ... >>>>> >>>>> Compiled with debug info: >>>>> ... >>>>> $ gcc test.c -g >>>>> ... >>>>> >>>>> When attempting to set a breakpoint at L1, which is a label without address: >>>>> ... >>>>> <1>: Abbrev Number: 2 (DW_TAG_subprogram) >>>>> DW_AT_name : main >>>>> <2><115>: Abbrev Number: 3 (DW_TAG_label) >>>>> <116> DW_AT_name : L1 >>>>> <119> DW_AT_decl_file : 1 >>>>> <11a> DW_AT_decl_line : 5 >>>>> <2><11b>: Abbrev Number: 0 >>>> Is this a debug info bug, >>> Strictly speaking, this is a debug info bug. The standard says that: >>> ... >>> The label entry has a DW_AT_low_pc attribute whose value is the address >>> of the first executable instruction for the location identified by the >>> label in the source program. >>> ... >>> >>> But I interpret the missing DW_AT_low_pc attribute as: there is a label >>> in the source, but the corresponding code has been optimized out. >>> >>>> or is the debug info telling us that the >>>> address of the label is the same as the line number's address? >>>> >>>> How about looking up the line number address instead of throwing >>>> an error? >>>> >>> Well, in this particular case, that wouldn't help. >>> >>> With L1 at line 3: >>> ... >>> $ cat -n test.c >>> 1 int main (void) { >>> 2 return 0; >>> 3 L1: >>> 4 (void)0; >>> 5 } >>> 6 >>> ... >>> there's no corresponding address: >>> ... >>> $ readelf -wL a.out >>> CU: test.c: >>> File name Line number Starting address >>> View Stmt >>> test.c 1 0x400497 >>> x >>> test.c 2 0x40049b >>> x >>> test.c 5 0x4004a0 >>> x >>> test.c - 0x4004a2 >>> ... >>> >>> My suspicion is that this won't be useful in general. >>> >> I've pushed this as attached below, with the test-case updated to work >> around PR26546 - "[pie] Setting breakpoint on missing label sets >> breakpoint at offset 0 in NULL section" ( >> https://sourceware.org/bugzilla/show_bug.cgi?id=26546 ). > Which is fixed by the patch below. > > Any comments? > I've committed this. Thanks, - Tom > > 0001-gdb-breakpoint-PIE-Handle-setting-breakpoint-on-label-without-address.patch > > [gdb/breakpoint, PIE] Handle setting breakpoint on label without address > > When adding: > ... > if ![runto_main] then { > fail "can't run to main" > return 0 > } > ... > to test-case gdb.base/label-without-address.exp and running it with target > board unix/-fPIE/-pie, we run into: > ... > (gdb) break main:L1^M > Breakpoint 2 at 0x555555554000: file label-without-address.c, line 22.^M > ... > That is, for a label with optimized-out address, we set a breakpoint at the > relocation base. > > The root cause is that the dwarf reader, despite finding that attribute > DW_AT_low_pc is missing, still tags the L1 symbol as having LOC_LABEL, which > means it has a valid address, which defaults to 0. > > Fix this by instead tagging the L1 symbol with LOC_OPTIMIZED_OUT. > > Tested on x86_64-linux. > > gdb/ChangeLog: > > 2020-08-28 Tom de Vries > > PR breakpoint/26546 > * dwarf2/read.c (new_symbol): Tag label symbol without DW_AT_low_pc as > LOC_OPTIMIZED_OUT instead of LOC_LABEL. > > gdb/testsuite/ChangeLog: > > 2020-08-28 Tom de Vries > > PR breakpoint/26546 > * gdb.base/label-without-address.exp: Runto main first. > > --- > gdb/dwarf2/read.c | 4 +++- > gdb/testsuite/gdb.base/label-without-address.exp | 5 +++++ > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c > index 0ac8533263..b37f7e7a2f 100644 > --- a/gdb/dwarf2/read.c > +++ b/gdb/dwarf2/read.c > @@ -21447,10 +21447,12 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu, > addr = attr->value_as_address (); > addr = gdbarch_adjust_dwarf2_addr (gdbarch, addr + baseaddr); > SET_SYMBOL_VALUE_ADDRESS (sym, addr); > + SYMBOL_ACLASS_INDEX (sym) = LOC_LABEL; > } > + else > + SYMBOL_ACLASS_INDEX (sym) = LOC_OPTIMIZED_OUT; > SYMBOL_TYPE (sym) = objfile_type (objfile)->builtin_core_addr; > SYMBOL_DOMAIN (sym) = LABEL_DOMAIN; > - SYMBOL_ACLASS_INDEX (sym) = LOC_LABEL; > add_symbol_to_list (sym, cu->list_in_scope); > break; > case DW_TAG_subprogram: > diff --git a/gdb/testsuite/gdb.base/label-without-address.exp b/gdb/testsuite/gdb.base/label-without-address.exp > index 0fcb1fd19a..c688149cf3 100644 > --- a/gdb/testsuite/gdb.base/label-without-address.exp > +++ b/gdb/testsuite/gdb.base/label-without-address.exp > @@ -19,6 +19,11 @@ if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} { > return -1 > } > > +if ![runto_main] then { > + fail "can't run to main" > + return 0 > +} > + > set supported 0 > gdb_test_multiple "l main:L1" "" { > -wrap -re "No label \"L1\" defined in function \"main\"\." { >