old-cross-binutils/gdb/target/waitstatus.h
Pedro Alves 863d01bde2 gdbserver: Fix non-stop / fork / step-over issues
Ref: https://sourceware.org/ml/gdb-patches/2015-07/msg00868.html

This adds a test that has a multithreaded program have several threads
continuously fork, while another thread continuously steps over a
breakpoint.

This exposes several intertwined issues, which this patch addresses:

 - When we're stopping and suspending threads, some thread may fork,
   and we missed setting its suspend count to 1, like we do when a new
   clone/thread is detected.  When we next unsuspend threads, the fork
   child's suspend count goes below 0, which is bogus and fails an
   assertion.

 - If a step-over is cancelled because a signal arrives, but then gdb
   is not interested in the signal, we pass the signal straight back
   to the inferior.  However, we miss that we need to re-increment the
   suspend counts of all other threads that had been paused for the
   step-over.  As a result, other threads indefinitely end up stuck
   stopped.

 - If a detach request comes in just while gdbserver is handling a
   step-over (in the test at hand, this is GDB detaching the fork
   child), gdbserver internal errors in stabilize_thread's helpers,
   which assert that all thread's suspend counts are 0 (otherwise we
   wouldn't be able to move threads out of the jump pads).  The
   suspend counts aren't 0 while a step-over is in progress, because
   all threads but the one stepping past the breakpoint must remain
   paused until the step-over finishes and the breakpoint can be
   reinserted.

 - Occasionally, we see "BAD - reinserting but not stepping." being
   output (from within linux_resume_one_lwp_throw).  That was because
   GDB pokes memory while gdbserver is busy with a step-over, and that
   suspends threads, and then re-resumes them with proceed_one_lwp,
   which missed another reason to tell linux_resume_one_lwp that the
   thread should be set back to stepping.

 - In a couple places, we were resuming threads that are meant to be
   suspended.  E.g., when a vCont;c/s request for thread B comes in
   just while gdbserver is stepping thread A past a breakpoint.  The
   resume for thread B must be deferred until the step-over finishes.

 - The test runs with both "set detach-on-fork" on and off.  When off,
   it exercises the case of GDB detaching the fork child explicitly.
   When on, it exercises the case of gdb resuming the child
   explicitly.  In the "off" case, gdb seems to exponentially become
   slower as new inferiors are created.  This is _very_ noticeable as
   with only 100 inferiors gdb is crawling already, which makes the
   test take quite a bit to run.  For that reason, I've disabled the
   "off" variant for now.

gdb/ChangeLog:
2015-08-06  Pedro Alves  <palves@redhat.com>

	* target/waitstatus.h (enum target_stop_reason)
	<TARGET_STOPPED_BY_SINGLE_STEP>: New value.

gdb/gdbserver/ChangeLog:
2015-08-06  Pedro Alves  <palves@redhat.com>

	* linux-low.c (handle_extended_wait): Set the fork child's suspend
	count if stopping and suspending threads.
	(check_stopped_by_breakpoint): If stopped by trace, set the LWP's
	stop reason to TARGET_STOPPED_BY_SINGLE_STEP.
	(linux_detach): Complete an ongoing step-over.
	(lwp_suspended_inc, lwp_suspended_decr): New functions.  Use
	throughout.
	(resume_stopped_resumed_lwps): Don't resume a suspended thread.
	(linux_wait_1): If passing a signal to the inferior after
	finishing a step-over, unsuspend and re-resume all lwps.  If we
	see a single-step event but the thread should be continuing, don't
	pass the trap to gdb.
	(stuck_in_jump_pad_callback, move_out_of_jump_pad_callback): Use
	internal_error instead of gdb_assert.
	(enqueue_pending_signal): New function.
	(check_ptrace_stopped_lwp_gone): Add debug output.
	(start_step_over): Use internal_error instead of gdb_assert.
	(complete_ongoing_step_over): New function.
	(linux_resume_one_thread): Don't resume a suspended thread.
	(proceed_one_lwp): If the LWP is stepping over a breakpoint, reset
	it stepping.

gdb/testsuite/ChangeLog:
2015-08-06  Pedro Alves  <palves@redhat.com>

	* gdb.threads/forking-threads-plus-breakpoint.exp: New file.
	* gdb.threads/forking-threads-plus-breakpoint.c: New file.
2015-08-06 10:30:18 +01:00

146 lines
4.7 KiB
C

/* Target waitstatus definitions and prototypes.
Copyright (C) 1990-2015 Free Software Foundation, Inc.
This file is part of GDB.
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/>. */
#ifndef WAITSTATUS_H
#define WAITSTATUS_H
#include "gdb_signals.h"
/* Stuff for target_wait. */
/* Generally, what has the program done? */
enum target_waitkind
{
/* The program has exited. The exit status is in value.integer. */
TARGET_WAITKIND_EXITED,
/* The program has stopped with a signal. Which signal is in
value.sig. */
TARGET_WAITKIND_STOPPED,
/* The program has terminated with a signal. Which signal is in
value.sig. */
TARGET_WAITKIND_SIGNALLED,
/* The program is letting us know that it dynamically loaded
something (e.g. it called load(2) on AIX). */
TARGET_WAITKIND_LOADED,
/* The program has forked. A "related" process' PTID is in
value.related_pid. I.e., if the child forks, value.related_pid
is the parent's ID. */
TARGET_WAITKIND_FORKED,
/* The program has vforked. A "related" process's PTID is in
value.related_pid. */
TARGET_WAITKIND_VFORKED,
/* The program has exec'ed a new executable file. The new file's
pathname is pointed to by value.execd_pathname. */
TARGET_WAITKIND_EXECD,
/* The program had previously vforked, and now the child is done
with the shared memory region, because it exec'ed or exited.
Note that the event is reported to the vfork parent. This is
only used if GDB did not stay attached to the vfork child,
otherwise, a TARGET_WAITKIND_EXECD or
TARGET_WAITKIND_EXIT|SIGNALLED event associated with the child
has the same effect. */
TARGET_WAITKIND_VFORK_DONE,
/* The program has entered or returned from a system call. On
HP-UX, this is used in the hardware watchpoint implementation.
The syscall's unique integer ID number is in
value.syscall_id. */
TARGET_WAITKIND_SYSCALL_ENTRY,
TARGET_WAITKIND_SYSCALL_RETURN,
/* Nothing happened, but we stopped anyway. This perhaps should
be handled within target_wait, but I'm not sure target_wait
should be resuming the inferior. */
TARGET_WAITKIND_SPURIOUS,
/* An event has occured, but we should wait again.
Remote_async_wait() returns this when there is an event
on the inferior, but the rest of the world is not interested in
it. The inferior has not stopped, but has just sent some output
to the console, for instance. In this case, we want to go back
to the event loop and wait there for another event from the
inferior, rather than being stuck in the remote_async_wait()
function. This way the event loop is responsive to other events,
like for instance the user typing. */
TARGET_WAITKIND_IGNORE,
/* The target has run out of history information,
and cannot run backward any further. */
TARGET_WAITKIND_NO_HISTORY,
/* There are no resumed children left in the program. */
TARGET_WAITKIND_NO_RESUMED
};
struct target_waitstatus
{
enum target_waitkind kind;
/* Additional information about the event. */
union
{
/* Exit status */
int integer;
/* Signal number */
enum gdb_signal sig;
/* Forked child pid */
ptid_t related_pid;
/* execd pathname */
char *execd_pathname;
/* Syscall number */
int syscall_number;
} value;
};
/* Extended reasons that can explain why a target/thread stopped for a
trap signal. */
enum target_stop_reason
{
/* Either not stopped, or stopped for a reason that doesn't require
special tracking. */
TARGET_STOPPED_BY_NO_REASON,
/* Stopped by a software breakpoint. */
TARGET_STOPPED_BY_SW_BREAKPOINT,
/* Stopped by a hardware breakpoint. */
TARGET_STOPPED_BY_HW_BREAKPOINT,
/* Stopped by a watchpoint. */
TARGET_STOPPED_BY_WATCHPOINT,
/* Stopped by a single step finishing. */
TARGET_STOPPED_BY_SINGLE_STEP
};
/* Prototypes */
/* Return a pretty printed form of target_waitstatus.
Space for the result is malloc'd, caller must free. */
extern char *target_waitstatus_to_string (const struct target_waitstatus *);
#endif /* WAITSTATUS_H */