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[143.159.223.185]) by smtp.gmail.com with ESMTPSA id l22-20020aa7c316000000b00568c299eaedsm1023326edq.81.2024.03.23.09.39.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 Mar 2024 09:39:45 -0700 (PDT) From: Andrew Burgess To: "H.J. Lu" , gdb-patches@sourceware.org Cc: felix.willgerodt@intel.com, jhb@FreeBSD.org Subject: Re: [PATCH v2] gdbserver: Clear X86_XSTATE_MPX bits in xcr0 on x32 In-Reply-To: <87edc1tcdd.fsf@redhat.com> References: <20240320111318.117728-1-hjl.tools@gmail.com> <87edc1tcdd.fsf@redhat.com> Date: Sat, 23 Mar 2024 16:39:44 +0000 Message-ID: <87bk74uckv.fsf@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-11.8 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_NUMSUBJECT, KAM_SHORT, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces+public-inbox=simark.ca@sourceware.org Andrew Burgess writes: > "H.J. Lu" writes: > >> Since MPX isn't available for x32, we should clear X86_XSTATE_MPX bits >> on x32. >> >> PR server/31511 >> * linux-x86-low.cc (x86_linux_read_description): Clear >> X86_XSTATE_MPX bits in xcr0 on x32. >> --- >> gdbserver/linux-x86-low.cc | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/gdbserver/linux-x86-low.cc b/gdbserver/linux-x86-low.cc >> index 3af0a009052..933d1fb012a 100644 >> --- a/gdbserver/linux-x86-low.cc >> +++ b/gdbserver/linux-x86-low.cc >> @@ -938,6 +938,10 @@ x86_linux_read_description (void) >> xcr0 = xstateregs[(I386_LINUX_XSAVE_XCR0_OFFSET >> / sizeof (uint64_t))]; >> >> + /* No MPX on x32. */ >> + if (machine == EM_X86_64 && !is_elf64) >> + xcr0 &= ~X86_XSTATE_MPX; > > Hi, > > I have a series in flight that conflicts with this change: > > https://inbox.sourceware.org/gdb-patches/cover.1706801009.git.aburgess@redhat.com > > And so I'm trying to resolve the conflicts. OK, I think I may have resolved the conflict. I'm still unable to test x32 ABI, would you mind applying this series: https://inbox.sourceware.org/gdb-patches/cover.1711211528.git.aburgess@redhat.com and checking that your x32 use case still behaves as you expect. The merge of our work occurs in this patch: https://inbox.sourceware.org/gdb-patches/a76168beacd9bb79b72ca1a0d26995abd770104c.1711211528.git.aburgess@redhat.com Also, I invite you to take a look at this additional patch which adds an extra assert that relates to your work: https://inbox.sourceware.org/gdb-patches/159cadba5ba824579cbc6426cb26f45228eda0a7.1711211528.git.aburgess@redhat.com Any feedback would be great. Thanks, Andrew > > Initially I thought I could test this by compiling something with the > gcc -m32 option, but I now believe that is wrong, and I'd actually need > to compile using -mx32, is this correct? > > Gcc seems to understand this option, but I appear to be missing the > required development libraries, and I'm currently struggling to figure > out what I'd need to install. Can you suggest a particular > distro/version that should have the required development libraries > available? Or maybe I'm just not understanding something here and you > can point out what I'd doing wrong. > > The series of mine above came about for one reason: the `machine` type > checks in the gdbserver are not a good idea, they rely on access to an > executable, which isn't always available (e.g. if gdbserver attaches to > a running process for which the executable is not available). When I > started looking at this code I then decided to merge the whole target > description logic between GDB and gdbserver for x86/linux. > > Which leads onto my second question; you changed the gdbserver code, but > not the GDB code. Was this just an oversight? Or is there some reason > why this fix doesn't need making for GDB too? > > Now worryingly, on the GDB side, in > x86_linux_nat_target::read_description (gdb/x86-linux-nat.c) we do have > a variable `is_x32` which I sounds like it should be true when we are > debugging an x32 process.... but.... this variable is true for a binary > compiled with the -m32 flag, which I don't think is right. If my > understanding is correct then a -m32 binary is one compiled on an x86-64 > machine, but which is uses 32-bit int/pointer types, and which only uses > i386 instructions, and can use MPX, right? > > To summarise: > > 1. How might I go about compiling an x32 binary? > > 2. How can we detect an x32 process without checking the machine type? > > 3. Should your fix above be applied on the GDB side too? > > I've included below my initial attempt at a test for this change, > currently it compiles with -m32 as (like I said) -mx32 doesn't work on > my machine. I've been testing this: > > make check-gdb TESTS="gdb.arch/amd64-x32-no-mpx-in-tdesc.exp" \ > RUNTESTFLAGS="--target_board=unix" > make check-gdb TESTS="gdb.arch/amd64-x32-no-mpx-in-tdesc.exp" \ > RUNTESTFLAGS="--target_board=native-gdbserver" > make check-gdb TESTS="gdb.arch/amd64-x32-no-mpx-in-tdesc.exp" \ > RUNTESTFLAGS="--target_board=native-extended-gdbserver" > > Currently it will fail for all as -m32 != -mx32 and the .mpx feature > shows up (as expected). > > I guess you have a target which supports -mx32, so on that target you > should be able to change the '-m32' in the test to '-mx32' and I would > expect you to see the test pass for the gdbserver boards, but fail on > the unix board. > > Thanks, > Andrew > > --- > > commit 22167bc5c2f2770e1b1a3f0eb0569df3140921e8 > Author: Andrew Burgess > Date: Sat Mar 23 10:45:22 2024 +0000 > > WIP: New test > > diff --git a/gdb/testsuite/gdb.arch/amd64-x32-no-mpx-in-tdesc.c b/gdb/testsuite/gdb.arch/amd64-x32-no-mpx-in-tdesc.c > new file mode 100644 > index 00000000000..e2119ba7d92 > --- /dev/null > +++ b/gdb/testsuite/gdb.arch/amd64-x32-no-mpx-in-tdesc.c > @@ -0,0 +1,22 @@ > +/* This testcase is part of GDB, the GNU debugger. > + > + Copyright 2024 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 . */ > + > +int > +main (void) > +{ > + return 0; > +} > diff --git a/gdb/testsuite/gdb.arch/amd64-x32-no-mpx-in-tdesc.exp b/gdb/testsuite/gdb.arch/amd64-x32-no-mpx-in-tdesc.exp > new file mode 100644 > index 00000000000..78e0d948348 > --- /dev/null > +++ b/gdb/testsuite/gdb.arch/amd64-x32-no-mpx-in-tdesc.exp > @@ -0,0 +1,52 @@ > +# Copyright 2024 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 . > +# > +# This file is part of the gdb testsuite. > + > +# Check that the mpx feature is not present in the target description > +# when debugging x32 binaries on an x86-64 target. > + > +require {istarget x86_64-*-*} > + > +standard_testfile > +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} \ > + {debug additional_flags=-m32}] } { > + return -1 > +} > + > +if ![runto_main] { > + return -1 > +} > + > +set found_mpx false > +gdb_test_multiple "maint print xml-tdesc" "" { > + -re "^maint print xml-tdesc\r\n" { > + exp_continue > + } > + > + -re "^\\s+\r\n" { > + set found_mpx true > + exp_continue > + } > + > + -re "^$gdb_prompt $" { > + gdb_assert { !$found_mpx } \ > + "mpx feature not in target description" > + } > + > + -re "^\[^\r\n\]+\r\n" { > + exp_continue > + } > +}