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 60FF23894C3B for ; Fri, 28 Aug 2020 13:20:55 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 60FF23894C3B 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 3B4AEB5C8; Fri, 28 Aug 2020 13:21:27 +0000 (UTC) Subject: [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> 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: <205b09a4-d0d9-bf96-1c4b-fbe60dcde45c@suse.de> Date: Fri, 28 Aug 2020 15:20:53 +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: <79ab7968-bd35-aa3a-dd8b-37076609043d@suse.de> Content-Type: multipart/mixed; boundary="------------8F58E30293CEC0B06891AE21" Content-Language: en-US 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: Fri, 28 Aug 2020 13:20:57 -0000 This is a multi-part message in MIME format. --------------8F58E30293CEC0B06891AE21 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit [ 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? Thanks, - Tom --------------8F58E30293CEC0B06891AE21 Content-Type: text/x-patch; charset=UTF-8; name="0001-gdb-breakpoint-PIE-Handle-setting-breakpoint-on-label-without-address.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename*0="0001-gdb-breakpoint-PIE-Handle-setting-breakpoint-on-label-w"; filename*1="ithout-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\"\." { --------------8F58E30293CEC0B06891AE21--