| Message ID | 9039e000-1d8c-ffcc-60bd-659b3a983a43@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Friday, January 10, 2020 3:03 AM, Pedro Alves wrote: > > The changes around clear_symtab_users calls are necessary because > otherwise we regress gdb.base/step-over-exit.exp, hitting the new > assertion in switch_to_program_space_and_thread. The problem is, a > forked child terminates, and when GDB decides to auto-purge that > inferior, GDB tries to switch to the pspace of that no-longer-existing > inferior. > > The root of the problem is within the program_space destructor: > > program_space::~program_space () > { > ... > set_current_program_space (this); # (1) > ... > breakpoint_program_space_exit (this); # (2) > ... > free_all_objfiles (); # (3) > ... > } > > We get here from delete_inferior -> delete_program_space. > > So we're deleting an inferior, and the inferior to be > deleted is no longer in the inferior list. > > At (2), we've deleted all the breakpoints and locations for the > program space being deleted. > > The crash happens while doing a breakpoint re-set, called by > clear_symtab_users at the tail end of (3). That is, while recreating > breakpoints for the current program space, which is the program space > we're tearing down. During breakpoint re-set, we try to switch to the > new location's pspace (the current pspace set in (1), so the pspace > we're tearing down) with switch_to_program_space_and_thread, and that > hits the failed assertion. It's the fact that we recreate breakpoints > in the program_space destructor that is the latent bug here. Just > don't do that, since we've already taken care of breakpoints with > breakpoint_program_space_exit, and we don't end up in the crash situation. > > My first approach to fix this added a symfile_add_flags parameter to > program_space::free_all_objfiles, and then passed that down to > clear_symtab_users. The program_space dtor would then pass down > SYMFILE_DEFER_BP_RESET to free_all_objfiles. I couldn't help feeling > that adding that parameter to free_all_objfiles looked a little > awkward, so I settled on something a little different -- hoist the > clear_symtab_users call to the callers. There are only two callers. > I felt that that didn't look as odd, particularly since > remove_symbol_file_command also does: > > objf->unlink (); > clear_symtab_users (0); > > I.e., objfile deletion is already separate from calling > clear_symtab_users in some places. > > I'm not hard set on this approach though; I can go with adding the > symfile_add_flags parameter to program_space::free_all_objfiles if > people prefer that. I personally think that in particular the comment and the change below have educational value. So, I'd vote for the approach you sent. > diff --git a/gdb/progspace.c b/gdb/progspace.c > index 96f8acc64c..1361040347 100644 > --- a/gdb/progspace.c > +++ b/gdb/progspace.c > @@ -147,6 +147,9 @@ program_space::~program_space () > no_shared_libraries (NULL, 0); > exec_close (); > free_all_objfiles (); > + /* Defer breakpoint re-set because we don't want to create new > + locations for this pspace which we're tearing down. */ > + clear_symtab_users (SYMFILE_DEFER_BP_RESET); > if (!gdbarch_has_shared_address_space (target_gdbarch ())) > free_address_space (this->aspace); > clear_section_table (&this->target_sections); As far as I can tell, you rebased the series on the current master, correct? Could you update the users/palves/multi-target-v2 branch? The new patch does not apply there cleanly. I attempted to replicate it on users/palves/multi-target-v2, but gdb.base/step-over-exit.exp still hits the assertion. -Baris Intel Deutschland GmbH Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany Tel: +49 89 99 8853-0, www.intel.de Managing Directors: Christin Eisenschmid, Gary Kershaw Chairperson of the Supervisory Board: Nicole Lau Registered Office: Munich Commercial Register: Amtsgericht Muenchen HRB 186928
On 1/10/20 11:33 AM, Aktemur, Tankut Baris wrote: > As far as I can tell, you rebased the series on the current master, correct? > Could you update the users/palves/multi-target-v2 branch? The new patch does not > apply there cleanly. I attempted to replicate it on users/palves/multi-target-v2, > but gdb.base/step-over-exit.exp still hits the assertion. Sorry, should have thought to do that. Done now. Thanks, Pedro Alves
On Friday, January 10, 2020 1:18 PM, Pedro Alves wrote: > > > As far as I can tell, you rebased the series on the current master, correct? > > Could you update the users/palves/multi-target-v2 branch? The new patch does not > > apply there cleanly. I attempted to replicate it on users/palves/multi-target-v2, > > but gdb.base/step-over-exit.exp still hits the assertion. > Sorry, should have thought to do that. Done now. Got it, and ran the test without problems. Thank you. -Baris Intel Deutschland GmbH Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany Tel: +49 89 99 8853-0, www.intel.de Managing Directors: Christin Eisenschmid, Gary Kershaw Chairperson of the Supervisory Board: Nicole Lau Registered Office: Munich Commercial Register: Amtsgericht Muenchen HRB 186928
>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
Pedro> The crash happens while doing a breakpoint re-set, called by
Pedro> clear_symtab_users at the tail end of (3). That is, while recreating
Pedro> breakpoints for the current program space, which is the program space
Pedro> we're tearing down. During breakpoint re-set, we try to switch to the
Pedro> new location's pspace (the current pspace set in (1), so the pspace
Pedro> we're tearing down) with switch_to_program_space_and_thread, and that
Pedro> hits the failed assertion.
Whatever happened to fine-grained breakpoint resetting?
Among other things maybe that would help with this sort of problem.
Pedro> I'm not hard set on this approach though; I can go with adding the
Pedro> symfile_add_flags parameter to program_space::free_all_objfiles if
Pedro> people prefer that.
This approach seems fine.
Longer term I would like to get rid of clear_symtab_users. Maybe it
could be replaced with more precisely targeted observers instead.
thanks,
Tom
On 1/10/20 2:34 PM, Tom Tromey wrote: >>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes: > > Pedro> The crash happens while doing a breakpoint re-set, called by > Pedro> clear_symtab_users at the tail end of (3). That is, while recreating > Pedro> breakpoints for the current program space, which is the program space > Pedro> we're tearing down. During breakpoint re-set, we try to switch to the > Pedro> new location's pspace (the current pspace set in (1), so the pspace > Pedro> we're tearing down) with switch_to_program_space_and_thread, and that > Pedro> hits the failed assertion. > > Whatever happened to fine-grained breakpoint resetting? > Among other things maybe that would help with this sort of problem. Yeah... Many years ago Keith gave it a try, and then he had to go do something else. And then few years later, I gave it another go. I got to somewhere quite close to useful, but never managed to get back to finishing it. The branch doesn't look like is on my github, I'd have to dig it out. This was pre-C++... Maybe starting to scratch is better... > > Pedro> I'm not hard set on this approach though; I can go with adding the > Pedro> symfile_add_flags parameter to program_space::free_all_objfiles if > Pedro> people prefer that. > > This approach seems fine. > Longer term I would like to get rid of clear_symtab_users. Maybe it > could be replaced with more precisely targeted observers instead. Thanks, Pedro Alves
diff --git a/gdb/progspace-and-thread.c b/gdb/progspace-and-thread.c index a1824e8935..698661d43f 100644 --- a/gdb/progspace-and-thread.c +++ b/gdb/progspace-and-thread.c @@ -25,8 +25,9 @@ void switch_to_program_space_and_thread (program_space *pspace) { inferior *inf = find_inferior_for_program_space (pspace); + gdb_assert (inf != nullptr); - if (inf != NULL && inf->pid != 0) + if (inf->pid != 0) { thread_info *tp = any_live_thread_of_inferior (inf); @@ -39,6 +40,5 @@ switch_to_program_space_and_thread (program_space *pspace) } } - switch_to_no_thread (); - set_current_program_space (pspace); + switch_to_inferior_no_thread (inf); } diff --git a/gdb/progspace.c b/gdb/progspace.c index 96f8acc64c..1361040347 100644 --- a/gdb/progspace.c +++ b/gdb/progspace.c @@ -147,6 +147,9 @@ program_space::~program_space () no_shared_libraries (NULL, 0); exec_close (); free_all_objfiles (); + /* Defer breakpoint re-set because we don't want to create new + locations for this pspace which we're tearing down. */ + clear_symtab_users (SYMFILE_DEFER_BP_RESET); if (!gdbarch_has_shared_address_space (target_gdbarch ())) free_address_space (this->aspace); clear_section_table (&this->target_sections); @@ -168,8 +171,6 @@ program_space::free_all_objfiles () while (!objfiles_list.empty ()) objfiles_list.front ()->unlink (); - - clear_symtab_users (0); } /* See progspace.h. */ diff --git a/gdb/symfile.c b/gdb/symfile.c index 86d6174107..d5f70d7f03 100644 --- a/gdb/symfile.c +++ b/gdb/symfile.c @@ -1253,6 +1253,8 @@ symbol_file_clear (int from_tty) current_program_space->free_all_objfiles (); + clear_symtab_users (0); + gdb_assert (symfile_objfile == NULL); if (from_tty) printf_filtered (_("No symbol file now.\n")); diff --git a/gdb/testsuite/gdb.server/bkpt-other-inferior.exp b/gdb/testsuite/gdb.server/bkpt-other-inferior.exp new file mode 100644 index 0000000000..e2a7be5cdb --- /dev/null +++ b/gdb/testsuite/gdb.server/bkpt-other-inferior.exp @@ -0,0 +1,93 @@ +# Copyright 2019 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 <http://www.gnu.org/licenses/>. + +# Test that GDB does not access the remote target's memory when +# setting a breakpoint on a function that only exists in an inferior +# that is not bound to the remote target. + +load_lib gdbserver-support.exp + +standard_testfile server.c + +if { [skip_gdbserver_tests] } { + return 0 +} + +if { [prepare_for_testing "failed to prepare" ${binfile} "${srcfile}" \ + {debug pthreads}] } { + return +} + +# Make sure we're disconnected, in case we're testing with an +# extended-remote board, therefore already connected. +gdb_test "disconnect" ".*" + +# Leave inferior 1 with the exec target, not connected. Add another +# inferior, and connect it to gdbserver. + +gdb_test "add-inferior" "Added inferior 2" \ + "add inferior 2" +gdb_test "inferior 2" "Switching to inferior 2.*" \ + "switch to inferior 2" +gdb_test "file ${binfile}" ".*" "load file in inferior 2" + +set target_exec [gdbserver_download_current_prog] + +# Start GDBserver. +set res [gdbserver_start "" $target_exec] + +# Connect to GDBserver. +set gdbserver_protocol [lindex $res 0] +set gdbserver_gdbport [lindex $res 1] +gdb_target_cmd $gdbserver_protocol $gdbserver_gdbport + +# Discard any symbol files that we have opened. +set test "discard symbol table" +gdb_test_multiple "file" $test { + -re "A program is being debugged already..*Are you sure you want to change the file.*y or n. $" { + gdb_test "y" ".*" $test \ + {Discard symbol table from `.*'\? \(y or n\) } "y" + } +} + +# At this point: +# +# - inferior 1 has symbols, and is not connected to any target. +# - inferior 2 has no symbols, and is connected to gdbserver. + +# Setting a breakpoint at some function by name should set a +# breakpoint on inferior 1, since it has symbols, and should not +# result in any access to inferior 2's remote target. + +gdb_test_no_output "set debug remote 1" + +foreach inf_sel {1 2} { + with_test_prefix "inf $inf_sel" { + gdb_test "inferior $inf_sel" "Switching to inferior $inf_sel.*" \ + "switch to inferior" + + set test "set breakpoint" + gdb_test_multiple "break main" $test { + -re "Sending packet.*$gdb_prompt $" { + fail $test + } + -re "^break main\r\nBreakpoint .* at .*$gdb_prompt $" { + pass $test + } + } + + delete_breakpoints + } +}