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
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resume.h	Update year range in copyright notice of all files owned by the GDB project.	2015-01-01 13:32:14 +04:00
target.h	Revert the previous 7 commits of: Validate binary before use	2015-07-15 20:27:32 +02:00
wait.h	Update year range in copyright notice of all files owned by the GDB project.	2015-01-01 13:32:14 +04:00
waitstatus.c	Update year range in copyright notice of all files owned by the GDB project.	2015-01-01 13:32:14 +04:00
waitstatus.h	gdbserver: Fix non-stop / fork / step-over issues	2015-08-06 10:30:18 +01:00