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With multi-target, each inferior now has its own target connection.
The problem in switch_to_program_space_and_thread is that in the
current state GDB switches to "no thread" and also sets the program
space but because the inferior is not switched, potentially an
incorrect target remains selected.
Here is a sample scenario that exploits this flow:
On terminal 1, start a gdbserver on a program named foo:
$ gdbserver :1234 ./foo
On terminal 2, start gdb on a program named bar. Suppose foo and bar
are compiled from foo.c and bar.c. They are completely separate. So,
bar.c:2 has no meaning for foo.
$ gdb -q ./bar
Reading symbols from ./bar...
(gdb) add-inferior
[New inferior 2]
Added inferior 2
(gdb) inferior 2
[Switching to inferior 2 [<null>] (<noexec>)]
(gdb) target remote :1234
...
(gdb) set debug remote 2
(gdb) break bar.c:2
Sending packet: $Hgp0.0#ad...Packet received: OK
Sending packet: $m5fa,12#f8...Packet received: E01
Sending packet: $m5fa,1#c6...Packet received: E01
Sending packet: $m5fb,3#c9...Packet received: E01
Sending packet: $m5fe,1#ca...Packet received: E01
Breakpoint 1 at 0x5fe: file bar.c, line 2.
(gdb)
Here we have an unnecessary sending of the packets to the gdbserver.
With this fix in progspace-and-thread.c, we'll get this:
(gdb) break bar.c:2
Breakpoint 1 at 0x5fe: file bar.c, line 2.
(gdb)
Now there is no sending of the packets to gdbserver.
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, 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.
gdb/ChangeLog:
2020-01-10 Aleksandar Paunovic <aleksandar.paunovic@intel.com>
Pedro Alves <palves@redhat.com>
* progspace-and-thread.c (switch_to_program_space_and_thread):
Assert there's an inferior for PSPACE. Use
switch_to_inferior_no_thread to switch the inferior too.
* progspace.c (program_space::~program_space): Call
clear_symtab_users here, with SYMFILE_DEFER_BP_RESET.
(program_space::free_all_objfiles): Don't call clear_symtab_users
here.
* symfile.c (symbol_file_clear): Call clear_symtab_users here.
gdb/testsuite/ChangeLog:
2020-01-10 Pedro Alves <palves@redhat.com>
* gdb.server/bkpt-other-inferior.exp: New file.
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| bfd | ||
| binutils | ||
| config | ||
| contrib | ||
| cpu | ||
| elfcpp | ||
| etc | ||
| gas | ||
| gdb | ||
| gnulib | ||
| gold | ||
| gprof | ||
| include | ||
| intl | ||
| ld | ||
| libctf | ||
| libdecnumber | ||
| libiberty | ||
| opcodes | ||
| readline | ||
| sim | ||
| texinfo | ||
| zlib | ||
| .cvsignore | ||
| .gitattributes | ||
| .gitignore | ||
| ar-lib | ||
| ChangeLog | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| COPYING | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| COPYING.LIB | ||
| COPYING.LIBGLOSS | ||
| COPYING.NEWLIB | ||
| depcomp | ||
| djunpack.bat | ||
| install-sh | ||
| libtool.m4 | ||
| lt~obsolete.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| makefile.vms | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| multilib.am | ||
| README | ||
| README-maintainer-mode | ||
| setup.com | ||
| src-release.sh | ||
| symlink-tree | ||
| test-driver | ||
| ylwrap | ||
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.