From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by sourceware.org (Postfix) with ESMTPS id D99673857C65 for ; Wed, 10 Nov 2021 11:56:17 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org D99673857C65 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 10DAF218EF; Wed, 10 Nov 2021 11:56:17 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id EAEC013BFF; Wed, 10 Nov 2021 11:56:16 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id XNUmOGCzi2G0aQAAMHmgww (envelope-from ); Wed, 10 Nov 2021 11:56:16 +0000 Subject: Re: [PATCH][gdb/testsuite] Add gdb.opt/break-on-_exit.exp To: Kevin Buettner Cc: gdb-patches@sourceware.org References: <20211029192419.GA26416@delia> <2cc5e63d-5be1-a5c7-b1cd-6058223a5a19@suse.de> <20211102101329.565a324b@f35-m1> <33a30d8d-247e-fba8-c9f1-b8ff0bd001b2@suse.de> <20211109093517.2d6f07d3@f35-m3> <88bedd77-01f5-a5d3-694e-aa8410113f49@suse.de> <20211109102906.6d2b6e78@f35-m3> From: Tom de Vries Message-ID: Date: Wed, 10 Nov 2021 12:56:16 +0100 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: <20211109102906.6d2b6e78@f35-m3> Content-Type: multipart/mixed; boundary="------------8DA6170BB7EBE04E18985AF4" Content-Language: en-US X-Spam-Status: No, score=-13.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, NICE_REPLY_A, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) 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: Wed, 10 Nov 2021 11:56:20 -0000 This is a multi-part message in MIME format. --------------8DA6170BB7EBE04E18985AF4 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit On 11/9/21 6:29 PM, Kevin Buettner wrote: > On Tue, 9 Nov 2021 17:58:17 +0100 > Tom de Vries wrote: > >> On 11/9/21 5:35 PM, Kevin Buettner wrote: >>> On Thu, 4 Nov 2021 12:20:14 +0100 >>> Tom de Vries wrote: >>> >>>> [ was: Re: [PATCH][gdb/testsuite] Work around skip_prologue problems in >>>> gdb.threads/process-dies-while-detaching.exp ] >>>> >>>> On 11/2/21 6:13 PM, Kevin Buettner wrote: >>>>> On Tue, 2 Nov 2021 12:38:26 +0100 >>>>> Tom de Vries via Gdb-patches wrote: >>>>> >>>>>> On 10/29/21 9:24 PM, Tom de Vries via Gdb-patches wrote: >>>>>>> Hi, >>>>>>> >>>>>>> On powerpc64le-linux, I run into: >>>>>>> ... >>>>>>> [Inferior 1 (process 5156) exited normally]^M >>>>>>> (gdb) FAIL: gdb.threads/process-dies-while-detaching.exp: single-process: \ >>>>>>> detach: detach: continue to breakpoint: _exit (the program exited) >>>>>>> ... >>>>>>> >>>>>>> What happens is the following: >>>>>>> - a breakpoint is set on _exit, >>>>>>> - a continue is issued >>>>>>> - the continue is supposed to hit the breakpoint, but instead >>>>>>> the program exits. >>>>>>> >>>>>>> I traced this down to the breakpoint on _exit being set too far from function >>>>>>> entry. This is caused by the skip_prologue function (in rs6000-tdep.c) >>>>>>> optimistically ignoring insns it doesn't recognize. In particular, it walks >>>>>>> past the system call instruction "sc" which initiates the actual exit. >>>>>>> >>>>>>> While this needs fixing, >>>>>> >>>>>> Filed here: https://sourceware.org/bugzilla/show_bug.cgi?id=28527 . >>>>>> >>>>>> Submitted patch here: >>>>>> https://sourceware.org/pipermail/gdb-patches/2021-November/183016.html . >>>>>> >>>>>> Thanks, >>>>>> - Tom >>>>>> >>>>>>> we don't want to be testing this behaviour in this >>>>>>> test-case. >>>>> >>>>> Since you've fixed the problem in skip_prologue(), I'd prefer that this >>>>> testsuite patch not go in. >>>> >>>> One possible objection would be that otherwise we no longer excercise >>>> the problem, so here's a test-case for that. >>>> >>>> Any comments? >>> >>> I've been trying (and failing) to reproduce this by hand on Fedora 35 >>> ppc64le. Here's what I'm doing... >>> >>> [kev@f35-ppc64le-1 tmp]$ tail -9 break-on-_exit.c >>> #include >>> >>> int >>> main (void) >>> { >>> _exit (0); >>> >>> return 0; >>> } >>> [kev@f35-ppc64le-1 tmp]$ gcc -o break-on-_exit break-on-_exit.c >>> [kev@f35-ppc64le-1 tmp]$ gdb --readnever break-on-_exit >>> GNU gdb (GDB) Fedora 11.1-2.fc35 >>> Copyright (C) 2021 Free Software Foundation, Inc. >>> License GPLv3+: GNU GPL version 3 or later >>> This is free software: you are free to change and redistribute it. >>> There is NO WARRANTY, to the extent permitted by law. >>> Type "show copying" and "show warranty" for details. >>> This GDB was configured as "ppc64le-redhat-linux-gnu". >>> Type "show configuration" for configuration details. >>> For bug reporting instructions, please see: >>> . >>> Find the GDB manual and other documentation resources online at: >>> . >>> >>> For help, type "help". >>> Type "apropos word" to search for commands related to "word"... >>> Reading symbols from break-on-_exit... >>> (No debugging symbols found in break-on-_exit) >>> (gdb) start >>> Temporary breakpoint 1 at 0x10000708 >>> Starting program: /mesquite2/tmp/break-on-_exit >>> [Thread debugging using libthread_db enabled] >>> Using host libthread_db library "/lib64/libthread_db.so.1". >>> >>> Temporary breakpoint 1, 0x0000000010000708 in main () >>> (gdb) b _exit >>> Breakpoint 2 at 0x7ffff7decc1c (2 locations) >>> (gdb) info breakpoints >>> Num Type Disp Enb Address What >>> 2 breakpoint keep y >>> 2.1 y 0x00007ffff7decc1c <_exit+60> >>> 2.2 y 0x00007ffff7fc9970 <_exit+64> >>> (gdb) info shared >>> From To Syms Read Shared Object Library >>> 0x00007ffff7f91080 0x00007ffff7fcc224 Yes (*) /lib64/ld64.so.2 >>> 0x00007ffff7d00a80 0x00007ffff7eaebbc Yes (*) /lib64/libc.so.6 >>> (*): Shared library is missing debugging information. >>> (gdb) c >>> Continuing. >>> >>> Breakpoint 2, 0x00007ffff7decc1c in _exit () from /lib64/libc.so.6 >>> (gdb) x/20i _exit >>> 0x7ffff7decbe0 <_exit>: addis r2,r12,21 >>> 0x7ffff7decbe4 <_exit+4>: addi r2,r2,-23776 >>> 0x7ffff7decbe8 <_exit+8>: mflr r0 >>> 0x7ffff7decbec <_exit+12>: nop >>> 0x7ffff7decbf0 <_exit+16>: std r29,-24(r1) >>> 0x7ffff7decbf4 <_exit+20>: std r31,-8(r1) >>> 0x7ffff7decbf8 <_exit+24>: ld r9,-29160(r2) >>> 0x7ffff7decbfc <_exit+28>: mr r31,r3 >>> 0x7ffff7decc00 <_exit+32>: std r30,-16(r1) >>> 0x7ffff7decc04 <_exit+36>: add r29,r9,r13 >>> 0x7ffff7decc08 <_exit+40>: ld r9,-28776(r13) >>> 0x7ffff7decc0c <_exit+44>: li r30,-4096 >>> 0x7ffff7decc10 <_exit+48>: mr r3,r31 >>> 0x7ffff7decc14 <_exit+52>: andis. r9,r9,16 >>> 0x7ffff7decc18 <_exit+56>: std r0,16(r1) >>> => 0x7ffff7decc1c <_exit+60>: li r0,234 >>> 0x7ffff7decc20 <_exit+64>: beq 0x7ffff7decc74 <_exit+148> >>> 0x7ffff7decc24 <_exit+68>: nop >>> 0x7ffff7decc28 <_exit+72>: nop >>> 0x7ffff7decc2c <_exit+76>: ori r2,r2,0 >>> (gdb) >>> >> >> Hi Kevin, thanks for looking into this. >> >>> I'm guessing that _exit looks different in your environment? >> >> Indeed, as show in the log message of commit >> a50bdb99afe3ce2374407cbe7ddc625c1a0b74f7: >> ... >> Dump of assembler code for function _exit: >> 0x00007ffff7e42ea0 <+0>: 12 00 4c 3c addis r2,r12,18 >> 0x00007ffff7e42ea4 <+4>: 60 43 42 38 addi r2,r2,17248 >> 0x00007ffff7e42ea8 <+8>: 00 00 00 60 nop >> 0x00007ffff7e42eac <+12>: f8 ff e1 fb std r31,-8(r1) >> 0x00007ffff7e42eb0 <+16>: 78 1b 7f 7c mr r31,r3 >> 0x00007ffff7e42eb4 <+20>: f0 ff c1 fb std r30,-16(r1) >> 0x00007ffff7e42eb8 <+24>: ea 00 00 38 li r0,234 >> 0x00007ffff7e42ebc <+28>: a0 8b 22 e9 ld r9,-29792(r2) >> 0x00007ffff7e42ec0 <+32>: 78 fb e3 7f mr r3,r31 >> 0x00007ffff7e42ec4 <+36>: 14 6a c9 7f add r30,r9,r13 >> 0x00007ffff7e42ec8 <+40>: 02 00 00 44 sc >> 0x00007ffff7e42ecc <+44>: 26 00 00 7c mfcr r0 >> 0x00007ffff7e42ed0 <+48>: 00 10 09 74 andis. r9,r0,4096 >> ... >> >> That's is why I put the test-case in the gdb.opt dir: it will excercise >> the code provided by glibc, which tends to be optimized, and different >> across os instances. >> >> The fact that it's not necessarily reproducible across os instances is >> not great, but OTOH it means that we do exercise real life code (much >> like the original test-case setting a breakpoint on _exit does, but in a >> more minimal way). > > Thanks for the clarifications. > > I think your new test is okay Committed with some of those clarifications, as below. Thanks for the review, - Tom --------------8DA6170BB7EBE04E18985AF4 Content-Type: text/x-patch; charset=UTF-8; name="0001-gdb-testsuite-Add-gdb.opt-break-on-_exit.exp.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="0001-gdb-testsuite-Add-gdb.opt-break-on-_exit.exp.patch" [gdb/testsuite] Add gdb.opt/break-on-_exit.exp Add a test-case to excercise the problem scenario reported in PR28527 and fixed in commit a50bdb99afe "[gdb/tdep, rs6000] Don't skip system call in skip_prologue": - set a breakpoint on _exit, and - verify that it triggers. Note that this is not a regression test for that commit. Since the actual code in _exit may vary across os instances, we cannot guarantee that the problem will always trigger with this test-case. Rather, this test-case is a version of the original test-case (gdb.threads/process-dies-while-detaching.exp) that is minimal while still reproducing the problem reported in PR28527, in that same setting. The benefit of this test-case is that it exercise real-life code and may expose similar problems in other settings. Also, it provides a much easier test-case to investigate in case a similar problem occurs. Tested on x86_64-linux and ppc64le-linux. --- gdb/testsuite/gdb.opt/break-on-_exit.c | 26 +++++++++++++ gdb/testsuite/gdb.opt/break-on-_exit.exp | 66 ++++++++++++++++++++++++++++++++ 2 files changed, 92 insertions(+) diff --git a/gdb/testsuite/gdb.opt/break-on-_exit.c b/gdb/testsuite/gdb.opt/break-on-_exit.c new file mode 100644 index 00000000000..d8da66193a8 --- /dev/null +++ b/gdb/testsuite/gdb.opt/break-on-_exit.c @@ -0,0 +1,26 @@ +/* This testcase is part of GDB, the GNU debugger. + + Copyright 2021 Free Software Foundation, Inc. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +#include + +int +main (void) +{ + _exit (0); + + return 0; +} diff --git a/gdb/testsuite/gdb.opt/break-on-_exit.exp b/gdb/testsuite/gdb.opt/break-on-_exit.exp new file mode 100644 index 00000000000..38476412862 --- /dev/null +++ b/gdb/testsuite/gdb.opt/break-on-_exit.exp @@ -0,0 +1,66 @@ +# Copyright 2021 Free Software Foundation, Inc. + +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see . */ + +# Set a breakpoint on libc's _exit, and verify that it triggers. The function +# tends to do a syscall immediately after the prologue, and if the breakpoint is +# set past the syscall due to faulty prologue skipping, the breakpoint will not +# trigger. +# +# In particular, we're trying to excercise the instruction analysis +# functionality of prologue skipping. If the non-minimal symbols are +# read for libc, then that functionality might not be used because f.i. +# line-info is used instead. Also, if the minimal symbols are not read +# for libc, then the breakpoint is set on the exec-local _exit@plt instead, +# and that functionality will also not be used. +# +# We may get the required setup in case of a libc with misssing separate +# debuginfo, but we want the same effect if that debuginfo is installed. +# +# So, we use -readnever to read minimal symbols, but not non-miminal symbols. +# +# Because the code at _exit may be and usually is optimized, the test is in +# the gdb.opt directory. + +standard_testfile + +# See if we have target board readnow.exp or similar. +if { [lsearch -exact $GDBFLAGS -readnow] != -1 \ + || [lsearch -exact $GDBFLAGS --readnow] != -1 } { + untested "--readnever not allowed in combination with --readnow" + return -1 +} + +save_vars { GDBFLAGS } { + append GDBFLAGS " -readnever" + + if {[prepare_for_testing "failed to prepare" $testfile $srcfile nodebug]} { + return -1 + } +} + +if ![runto_main] then { + return 0 +} + +gdb_breakpoint "_exit" + +# Give some background information about the breakpoint(s) and corresponding +# the shared lib(s). +gdb_test "info breakpoints" +gdb_test "info shared" + +# If the skip_prologue analysis of _exit is too eager, we may not hit the +# breakpoint. +gdb_continue_to_breakpoint "_exit" "_exit \\(\\) .*" --------------8DA6170BB7EBE04E18985AF4--