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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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This is more preparation bits for multi-target support.
In a multi-target scenario, we need to address the case of different
processes/threads running on different targets that happen to have the
same PID/PTID. E.g., we can have both process 123 in target 1, and
process 123 in target 2, while they're in reality different processes
running on different machines. Or maybe we've loaded multiple
instances of the same core file. Etc.
To address this, in my WIP multi-target branch, threads and processes
are uniquely identified by the (process_stratum target_ops *, ptid_t)
and (process_stratum target_ops *, pid) tuples respectively. I.e.,
each process_stratum instance has its own thread/process number space.
As you can imagine, that requires passing around target_ops * pointers
in a number of functions where we're currently passing only a ptid_t
or an int. E.g., when we look up a thread_info object by ptid_t in
find_thread_ptid, the ptid_t alone isn't sufficient.
In many cases though, we already have the thread_info or inferior
pointer handy, but we "lose" it somewhere along the call stack, only
to look it up again by ptid_t/pid. Since thread_info or inferior
objects know their parent target, if we pass around thread_info or
inferior pointers when possible, we avoid having to add extra
target_ops parameters to many functions, and also, we eliminate a
number of by ptid_t/int lookups.
So that's what this patch does. In a bit more detail:
- Changes a number of functions and methods to take a thread_info or
inferior pointer instead of a ptid_t or int parameter.
- Changes a number of structure fields from ptid_t/int to inferior or
thread_info pointers.
- Uses the inferior_thread() function whenever possible instead of
inferior_ptid.
- Uses thread_info pointers directly when possible instead of the
is_running/is_stopped etc. routines that require a lookup.
- A number of functions are eliminated along the way, such as:
int valid_gdb_inferior_id (int num);
int pid_to_gdb_inferior_id (int pid);
int gdb_inferior_id_to_pid (int num);
int in_inferior_list (int pid);
- A few structures and places hold a thread_info pointer across
inferior execution, so now they take a strong reference to the
(refcounted) thread_info object to avoid the thread_info pointer
getting stale. This is done in enable_thread_stack_temporaries and
in the infcall.c code.
- Related, there's a spot in infcall.c where using a RAII object to
handle the refcount would be handy, so a gdb::ref_ptr specialization
for thread_info is added (thread_info_ref, in gdbthread.h), along
with a gdb_ref_ptr policy that works for all refcounted_object types
(in common/refcounted-object.h).
gdb/ChangeLog:
2018-06-21 Pedro Alves <palves@redhat.com>
* ada-lang.h (ada_get_task_number): Take a thread_info pointer
instead of a ptid_t. All callers adjusted.
* ada-tasks.c (ada_get_task_number): Likewise. All callers
adjusted.
(print_ada_task_info, display_current_task_id, task_command_1):
Adjust.
* breakpoint.c (watchpoint_in_thread_scope): Adjust to use
inferior_thread.
(breakpoint_kind): Adjust.
(remove_breakpoints_pid): Rename to ...
(remove_breakpoints_inf): ... this. Adjust to take an inferior
pointer. All callers adjusted.
(bpstat_clear_actions): Use inferior_thread.
(get_bpstat_thread): New.
(bpstat_do_actions): Use it.
(bpstat_check_breakpoint_conditions, bpstat_stop_status): Adjust
to take a thread_info pointer. All callers adjusted.
(set_longjmp_breakpoint_for_call_dummy, set_momentary_breakpoint)
(breakpoint_re_set_thread): Use inferior_thread.
* breakpoint.h (struct inferior): Forward declare.
(bpstat_stop_status): Update.
(remove_breakpoints_pid): Delete.
(remove_breakpoints_inf): New.
* bsd-uthread.c (bsd_uthread_target::wait)
(bsd_uthread_target::update_thread_list): Use find_thread_ptid.
* btrace.c (btrace_add_pc, btrace_enable, btrace_fetch)
(maint_btrace_packet_history_cmd)
(maint_btrace_clear_packet_history_cmd): Adjust.
(maint_btrace_clear_cmd, maint_info_btrace_cmd): Adjust to use
inferior_thread.
* cli/cli-interp.c: Include "inferior.h".
* common/refcounted-object.h (struct
refcounted_object_ref_policy): New.
* compile/compile-object-load.c: Include gdbthread.h.
(store_regs): Use inferior_thread.
* corelow.c (core_target::close): Use current_inferior.
(core_target_open): Adjust to use first_thread_of_inferior and use
the current inferior.
* ctf.c (ctf_target::close): Adjust to use current_inferior.
* dummy-frame.c (dummy_frame_id) <ptid>: Delete, replaced by ...
<thread>: ... this new field. All references adjusted.
(dummy_frame_pop, dummy_frame_discard, register_dummy_frame_dtor):
Take a thread_info pointer instead of a ptid_t.
* dummy-frame.h (dummy_frame_push, dummy_frame_pop)
(dummy_frame_discard, register_dummy_frame_dtor): Take a
thread_info pointer instead of a ptid_t.
* elfread.c: Include "inferior.h".
(elf_gnu_ifunc_resolver_stop, elf_gnu_ifunc_resolver_return_stop):
Use inferior_thread.
* eval.c (evaluate_subexp): Likewise.
* frame.c (frame_pop, has_stack_frames, find_frame_sal): Use
inferior_thread.
* gdb_proc_service.h (struct thread_info): Forward declare.
(struct ps_prochandle) <ptid>: Delete, replaced by ...
<thread>: ... this new field. All references adjusted.
* gdbarch.h, gdbarch.c: Regenerate.
* gdbarch.sh (get_syscall_number): Replace 'ptid' parameter with a
'thread' parameter. All implementations and callers adjusted.
* gdbthread.h (thread_info) <set_running>: New method.
(delete_thread, delete_thread_silent): Take a thread_info pointer
instead of a ptid.
(global_thread_id_to_ptid, ptid_to_global_thread_id): Delete.
(first_thread_of_process): Delete, replaced by ...
(first_thread_of_inferior): ... this new function. All callers
adjusted.
(any_live_thread_of_process): Delete, replaced by ...
(any_live_thread_of_inferior): ... this new function. All callers
adjusted.
(switch_to_thread, switch_to_no_thread): Declare.
(is_executing): Delete.
(enable_thread_stack_temporaries): Update comment.
<enable_thread_stack_temporaries>: Take a thread_info pointer
instead of a ptid_t. Incref the thread.
<~enable_thread_stack_temporaries>: Decref the thread.
<m_ptid>: Delete
<m_thr>: New.
(thread_stack_temporaries_enabled_p, push_thread_stack_temporary)
(get_last_thread_stack_temporary)
(value_in_thread_stack_temporaries, can_access_registers_thread):
Take a thread_info pointer instead of a ptid_t. All callers
adjusted.
* infcall.c (get_call_return_value): Use inferior_thread.
(run_inferior_call): Work with thread pointers instead of ptid_t.
(call_function_by_hand_dummy): Work with thread pointers instead
of ptid_t. Use thread_info_ref.
* infcmd.c (proceed_thread_callback): Access thread's state
directly.
(ensure_valid_thread, ensure_not_running): Use inferior_thread,
access thread's state directly.
(continue_command): Use inferior_thread.
(info_program_command): Use find_thread_ptid and access thread
state directly.
(proceed_after_attach_callback): Use thread state directly.
(notice_new_inferior): Take a thread_info pointer instead of a
ptid_t. All callers adjusted.
(exit_inferior): Take an inferior pointer instead of a pid. All
callers adjusted.
(exit_inferior_silent): New.
(detach_inferior): Delete.
(valid_gdb_inferior_id, pid_to_gdb_inferior_id)
(gdb_inferior_id_to_pid, in_inferior_list): Delete.
(detach_inferior_command, kill_inferior_command): Use
find_inferior_id instead of valid_gdb_inferior_id and
gdb_inferior_id_to_pid.
(inferior_command): Use inferior and thread pointers.
* inferior.h (struct thread_info): Forward declare.
(notice_new_inferior): Take a thread_info pointer instead of a
ptid_t. All callers adjusted.
(detach_inferior): Delete declaration.
(exit_inferior, exit_inferior_silent): Take an inferior pointer
instead of a pid. All callers adjusted.
(gdb_inferior_id_to_pid, pid_to_gdb_inferior_id, in_inferior_list)
(valid_gdb_inferior_id): Delete.
* infrun.c (follow_fork_inferior, proceed_after_vfork_done)
(handle_vfork_child_exec_or_exit, follow_exec): Adjust.
(struct displaced_step_inferior_state) <pid>: Delete, replaced by
...
<inf>: ... this new field.
<step_ptid>: Delete, replaced by ...
<step_thread>: ... this new field.
(get_displaced_stepping_state): Take an inferior pointer instead
of a pid. All callers adjusted.
(displaced_step_in_progress_any_inferior): Adjust.
(displaced_step_in_progress_thread): Take a thread pointer instead
of a ptid_t. All callers adjusted.
(displaced_step_in_progress, add_displaced_stepping_state): Take
an inferior pointer instead of a pid. All callers adjusted.
(get_displaced_step_closure_by_addr): Adjust.
(remove_displaced_stepping_state): Take an inferior pointer
instead of a pid. All callers adjusted.
(displaced_step_prepare_throw, displaced_step_prepare)
(displaced_step_fixup): Take a thread pointer instead of a ptid_t.
All callers adjusted.
(start_step_over): Adjust.
(infrun_thread_ptid_changed): Remove bit updating ptids in the
displaced step queue.
(do_target_resume): Adjust.
(fetch_inferior_event): Use inferior_thread.
(context_switch, get_inferior_stop_soon): Take an
execution_control_state pointer instead of a ptid_t. All callers
adjusted.
(switch_to_thread_cleanup): Delete.
(stop_all_threads): Use scoped_restore_current_thread.
* inline-frame.c: Include "gdbthread.h".
(inline_state) <inline_state>: Take a thread pointer instead of a
ptid_t. All callers adjusted.
<ptid>: Delete, replaced by ...
<thread>: ... this new field.
(find_inline_frame_state): Take a thread pointer instead of a
ptid_t. All callers adjusted.
(skip_inline_frames, step_into_inline_frame)
(inline_skipped_frames, inline_skipped_symbol): Take a thread
pointer instead of a ptid_t. All callers adjusted.
* inline-frame.h (skip_inline_frames, step_into_inline_frame)
(inline_skipped_frames, inline_skipped_symbol): Likewise.
* linux-fork.c (delete_checkpoint_command): Adjust to use thread
pointers directly.
* linux-nat.c (get_detach_signal): Likewise.
* linux-thread-db.c (thread_from_lwp): New 'stopped' parameter.
(thread_db_notice_clone): Adjust.
(thread_db_find_new_threads_silently)
(thread_db_find_new_threads_2, thread_db_find_new_threads_1): Take
a thread pointer instead of a ptid_t. All callers adjusted.
* mi/mi-cmd-var.c: Include "inferior.h".
(mi_cmd_var_update_iter): Update to use thread pointers.
* mi/mi-interp.c (mi_new_thread): Update to use the thread's
inferior directly.
(mi_output_running_pid, mi_inferior_count): Delete, bits factored
out to ...
(mi_output_running): ... this new function.
(mi_on_resume_1): Adjust to use it.
(mi_user_selected_context_changed): Adjust to use inferior_thread.
* mi/mi-main.c (proceed_thread): Adjust to use thread pointers
directly.
(interrupt_thread_callback): : Adjust to use thread and inferior
pointers.
* proc-service.c: Include "gdbthread.h".
(ps_pglobal_lookup): Adjust to use the thread's inferior directly.
* progspace-and-thread.c: Include "inferior.h".
* progspace.c: Include "inferior.h".
* python/py-exitedevent.c (create_exited_event_object): Adjust to
hold a reference to an inferior_object.
* python/py-finishbreakpoint.c (bpfinishpy_init): Adjust to use
inferior_thread.
* python/py-inferior.c (struct inferior_object): Give the type a
tag name instead of a typedef.
(python_on_normal_stop): No need to check if the current thread is
listed.
(inferior_to_inferior_object): Change return type to
inferior_object. All callers adjusted.
(find_thread_object): Delete, bits factored out to ...
(thread_to_thread_object): ... this new function.
* python/py-infthread.c (create_thread_object): Use
inferior_to_inferior_object.
(thpy_is_stopped): Use thread pointer directly.
(gdbpy_selected_thread): Use inferior_thread.
* python/py-record-btrace.c (btpy_list_object) <ptid>: Delete
field, replaced with ...
<thread>: ... this new field. All users adjusted.
(btpy_insn_or_gap_new): Drop const.
(btpy_list_new): Take a thread pointer instead of a ptid_t. All
callers adjusted.
* python/py-record.c: Include "gdbthread.h".
(recpy_insn_new, recpy_func_new): Take a thread pointer instead of
a ptid_t. All callers adjusted.
(gdbpy_current_recording): Use inferior_thread.
* python/py-record.h (recpy_record_object) <ptid>: Delete
field, replaced with ...
<thread>: ... this new field. All users adjusted.
(recpy_element_object) <ptid>: Delete
field, replaced with ...
<thread>: ... this new field. All users adjusted.
(recpy_insn_new, recpy_func_new): Take a thread pointer instead of
a ptid_t. All callers adjusted.
* python/py-threadevent.c: Include "gdbthread.h".
(get_event_thread): Use thread_to_thread_object.
* python/python-internal.h (struct inferior_object): Forward
declare.
(find_thread_object, find_inferior_object): Delete declarations.
(thread_to_thread_object, inferior_to_inferior_object): New
declarations.
* record-btrace.c: Include "inferior.h".
(require_btrace_thread): Use inferior_thread.
(record_btrace_frame_sniffer)
(record_btrace_tailcall_frame_sniffer): Use inferior_thread.
(get_thread_current_frame): Use scoped_restore_current_thread and
switch_to_thread.
(get_thread_current_frame): Use thread pointer directly.
(record_btrace_replay_at_breakpoint): Use thread's inferior
pointer directly.
* record-full.c: Include "inferior.h".
* regcache.c: Include "gdbthread.h".
(get_thread_arch_regcache): Use the inferior's address space
directly.
(get_thread_regcache, registers_changed_thread): New.
* regcache.h (get_thread_regcache(thread_info *thread)): New
overload.
(registers_changed_thread): New.
(remote_target) <remote_detach_1>: Swap order of parameters.
(remote_add_thread): <remote_add_thread>: Return the new thread.
(get_remote_thread_info(ptid_t)): New overload.
(remote_target::remote_notice_new_inferior): Use thread pointers
directly.
(remote_target::process_initial_stop_replies): Use
thread_info::set_running.
(remote_target::remote_detach_1, remote_target::detach)
(extended_remote_target::detach): Adjust.
* stack.c (frame_show_address): Use inferior_thread.
* target-debug.h (target_debug_print_thread_info_pp): New.
* target-delegates.c: Regenerate.
* target.c (default_thread_address_space): Delete.
(memory_xfer_partial_1): Use current_inferior.
(target_detach): Use current_inferior.
(target_thread_address_space): Delete.
(generic_mourn_inferior): Use current_inferior.
* target.h (struct target_ops) <thread_address_space>: Delete.
(target_thread_address_space): Delete.
* thread.c (init_thread_list): Use ALL_THREADS_SAFE. Use thread
pointers directly.
(delete_thread_1, delete_thread, delete_thread_silent): Take a
thread pointer instead of a ptid_t. Adjust all callers.
(ptid_to_global_thread_id, global_thread_id_to_ptid): Delete.
(first_thread_of_process): Delete, replaced by ...
(first_thread_of_inferior): ... this new function. All callers
adjusted.
(any_thread_of_process): Rename to ...
(any_thread_of_inferior): ... this, and take an inferior pointer.
(any_live_thread_of_process): Rename to ...
(any_live_thread_of_inferior): ... this, and take an inferior
pointer.
(thread_stack_temporaries_enabled_p, push_thread_stack_temporary)
(value_in_thread_stack_temporaries)
(get_last_thread_stack_temporary): Take a thread pointer instead
of a ptid_t. Adjust all callers.
(thread_info::set_running): New.
(validate_registers_access): Use inferior_thread.
(can_access_registers_ptid): Rename to ...
(can_access_registers_thread): ... this, and take a thread
pointer.
(print_thread_info_1): Adjust to compare thread pointers instead
of ptids.
(switch_to_no_thread, switch_to_thread): Make extern.
(scoped_restore_current_thread::~scoped_restore_current_thread):
Use m_thread pointer directly.
(scoped_restore_current_thread::scoped_restore_current_thread):
Use inferior_thread.
(thread_command): Use thread pointer directly.
(thread_num_make_value_helper): Use inferior_thread.
* top.c (execute_command): Use inferior_thread.
* tui/tui-interp.c: Include "inferior.h".
* varobj.c (varobj_create): Use inferior_thread.
(value_of_root_1): Use find_thread_global_id instead of
global_thread_id_to_ptid.
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