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7f5ef60532
TL;DR - if we step an instruction that is as long as
decr_pc_after_break (1-byte on x86) right after removing the
breakpoint at PC, in non-stop mode, adjust_pc_after_break adjusts the
PC, but it shouldn't.
In non-stop mode, when a breakpoint is removed, it is moved to the
"moribund locations" list. This is because other threads that are
running may have tripped on that breakpoint as well, and we haven't
heard about it. When a trap is reported, we check if perhaps it was
such a deleted breakpoint that caused the trap. If so, we also need
to adjust the PC (decr_pc_after_break).
Now, say that, on x86:
- a breakpoint was placed at an address where we have an instruction
of the same length as decr_pc_after_break on this arch (1 on x86).
- the breakpoint is removed, and thus put on the moribund locations
list.
- the thread is single-stepped.
As there's no breakpoint inserted at PC anymore, the single-step
actually executes the 1-byte instruction normally. GDB should _not_
adjust the PC for the resulting SIGTRAP. But, adjust_pc_after_break
confuses the step SIGTRAP reported for this single-step as being a
SIGTRAP for the moribund location of the breakpoint that used to be at
the previous PC, and so infrun applies the decr_pc_after_break
adjustment incorrectly.
The confusion comes from the special case mentioned in the comment:
static void
adjust_pc_after_break (struct execution_control_state *ecs)
{
...
As a special case, we could have hardware single-stepped a
software breakpoint. In this case (prev_pc == breakpoint_pc),
we also need to back up to the breakpoint address. */
if (thread_has_single_step_breakpoints_set (ecs->event_thread)
|| !ptid_equal (ecs->ptid, inferior_ptid)
|| !currently_stepping (ecs->event_thread)
|| (ecs->event_thread->stepped_breakpoint
&& ecs->event_thread->prev_pc == breakpoint_pc))
regcache_write_pc (regcache, breakpoint_pc);
The condition that incorrectly triggers is the
"ecs->event_thread->prev_pc == breakpoint_pc" one.
Afterwards, the next resume resume re-executes an instruction that had
already executed, which if you're lucky, results in the inferior
crashing. If you're unlucky, you'll get silent bad behavior...
The fix is to remember that we stepped a breakpoint. Turns out the
only case we step a breakpoint instruction today isn't covered by the
testsuite. It's the case of a 'handle nostop" signal arriving while a
step is in progress _and_ we have a software watchpoint, which forces
always single-stepping. This commit extends sigstep.exp to cover
that, and adds a new test for the adjust_pc_after_break issue.
Tested on x86_64 Fedora 20, native and gdbserver.
gdb/
2014-10-28 Pedro Alves <palves@redhat.com>
PR gdb/12623
* gdbthread.h (struct thread_info) <stepped_breakpoint>: New
field.
* infrun.c (resume) <stepping breakpoint instruction>: Set the
thread's stepped_breakpoint field. Skip if reverse debugging.
Add comment.
(init_thread_stepping_state, handle_signal_stop): Clear the
thread's stepped_breakpoint field.
gdb/testsuite/
2014-10-28 Pedro Alves <palves@redhat.com>
PR gdb/12623
* gdb.base/sigstep.c (no_handler): New global.
(main): If 'no_handler is true, set the signal handlers to
SIG_IGN.
* gdb.base/sigstep.exp (breakpoint_over_handler): Add
with_sw_watch and no_handler parameters. Handle them.
(top level) <stepping over handler when stopped at a breakpoint
test>: Add a test axis for testing with a software watchpoint, and
another for testing with the signal handler set to SIG_IGN.
* gdb.base/step-sw-breakpoint-adjust-pc.c: New file.
* gdb.base/step-sw-breakpoint-adjust-pc.exp: New file.
471 lines
17 KiB
C
471 lines
17 KiB
C
/* Multi-process/thread control defs for GDB, the GNU debugger.
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Copyright (C) 1987-2014 Free Software Foundation, Inc.
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Contributed by Lynx Real-Time Systems, Inc. Los Gatos, CA.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef GDBTHREAD_H
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#define GDBTHREAD_H
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struct symtab;
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#include "breakpoint.h"
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#include "frame.h"
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#include "ui-out.h"
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#include "inferior.h"
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#include "btrace.h"
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/* Frontend view of the thread state. Possible extensions: stepping,
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finishing, until(ling),... */
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enum thread_state
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{
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THREAD_STOPPED,
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THREAD_RUNNING,
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THREAD_EXITED,
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};
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/* Inferior thread specific part of `struct infcall_control_state'.
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Inferior process counterpart is `struct inferior_control_state'. */
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struct thread_control_state
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{
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/* User/external stepping state. */
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/* Step-resume or longjmp-resume breakpoint. */
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struct breakpoint *step_resume_breakpoint;
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/* Exception-resume breakpoint. */
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struct breakpoint *exception_resume_breakpoint;
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/* Breakpoints used for software single stepping. Plural, because
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it may have multiple locations. E.g., if stepping over a
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conditional branch instruction we can't decode the condition for,
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we'll need to put a breakpoint at the branch destination, and
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another at the instruction after the branch. */
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struct breakpoint *single_step_breakpoints;
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/* Range to single step within.
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If this is nonzero, respond to a single-step signal by continuing
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to step if the pc is in this range.
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If step_range_start and step_range_end are both 1, it means to
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step for a single instruction (FIXME: it might clean up
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wait_for_inferior in a minor way if this were changed to the
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address of the instruction and that address plus one. But maybe
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not). */
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CORE_ADDR step_range_start; /* Inclusive */
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CORE_ADDR step_range_end; /* Exclusive */
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/* If GDB issues a target step request, and this is nonzero, the
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target should single-step this thread once, and then continue
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single-stepping it without GDB core involvement as long as the
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thread stops in the step range above. If this is zero, the
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target should ignore the step range, and only issue one single
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step. */
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int may_range_step;
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/* Stack frame address as of when stepping command was issued.
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This is how we know when we step into a subroutine call, and how
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to set the frame for the breakpoint used to step out. */
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struct frame_id step_frame_id;
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/* Similarly, the frame ID of the underlying stack frame (skipping
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any inlined frames). */
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struct frame_id step_stack_frame_id;
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/* Nonzero if we are presently stepping over a breakpoint.
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If we hit a breakpoint or watchpoint, and then continue, we need
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to single step the current thread with breakpoints disabled, to
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avoid hitting the same breakpoint or watchpoint again. And we
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should step just a single thread and keep other threads stopped,
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so that other threads don't miss breakpoints while they are
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removed.
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So, this variable simultaneously means that we need to single
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step the current thread, keep other threads stopped, and that
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breakpoints should be removed while we step.
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This variable is set either:
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- in proceed, when we resume inferior on user's explicit request
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- in keep_going, if handle_inferior_event decides we need to
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step over breakpoint.
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The variable is cleared in normal_stop. The proceed calls
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wait_for_inferior, which calls handle_inferior_event in a loop,
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and until wait_for_inferior exits, this variable is changed only
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by keep_going. */
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int trap_expected;
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/* Nonzero if the thread is being proceeded for a "finish" command
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or a similar situation when stop_registers should be saved. */
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int proceed_to_finish;
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/* Nonzero if the thread is being proceeded for an inferior function
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call. */
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int in_infcall;
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enum step_over_calls_kind step_over_calls;
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/* Nonzero if stopped due to a step command. */
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int stop_step;
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/* Chain containing status of breakpoint(s) the thread stopped
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at. */
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bpstat stop_bpstat;
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/* The interpreter that issued the execution command. NULL if the
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thread was resumed as a result of a command applied to some other
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thread (e.g., "next" with scheduler-locking off). */
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struct interp *command_interp;
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};
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/* Inferior thread specific part of `struct infcall_suspend_state'.
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Inferior process counterpart is `struct inferior_suspend_state'. */
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struct thread_suspend_state
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{
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/* Last signal that the inferior received (why it stopped). When
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the thread is resumed, this signal is delivered. Note: the
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target should not check whether the signal is in pass state,
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because the signal may have been explicitly passed with the
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"signal" command, which overrides "handle nopass". If the signal
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should be suppressed, the core will take care of clearing this
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before the target is resumed. */
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enum gdb_signal stop_signal;
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};
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struct thread_info
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{
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struct thread_info *next;
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ptid_t ptid; /* "Actual process id";
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In fact, this may be overloaded with
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kernel thread id, etc. */
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int num; /* Convenient handle (GDB thread id) */
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/* The name of the thread, as specified by the user. This is NULL
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if the thread does not have a user-given name. */
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char *name;
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/* Non-zero means the thread is executing. Note: this is different
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from saying that there is an active target and we are stopped at
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a breakpoint, for instance. This is a real indicator whether the
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thread is off and running. */
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int executing;
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/* Frontend view of the thread state. Note that the THREAD_RUNNING/
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THREAD_STOPPED states are different from EXECUTING. When the
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thread is stopped internally while handling an internal event,
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like a software single-step breakpoint, EXECUTING will be false,
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but STATE will still be THREAD_RUNNING. */
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enum thread_state state;
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/* If this is > 0, then it means there's code out there that relies
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on this thread being listed. Don't delete it from the lists even
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if we detect it exiting. */
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int refcount;
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/* State of GDB control of inferior thread execution.
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See `struct thread_control_state'. */
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struct thread_control_state control;
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/* State of inferior thread to restore after GDB is done with an inferior
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call. See `struct thread_suspend_state'. */
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struct thread_suspend_state suspend;
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int current_line;
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struct symtab *current_symtab;
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/* Internal stepping state. */
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/* Record the pc of the thread the last time it stopped. This is
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maintained by proceed and keep_going, and used in
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adjust_pc_after_break to distinguish a hardware single-step
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SIGTRAP from a breakpoint SIGTRAP. */
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CORE_ADDR prev_pc;
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/* Did we set the thread stepping a breakpoint instruction? This is
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used in conjunction with PREV_PC to decide whether to adjust the
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PC. */
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int stepped_breakpoint;
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/* Should we step over breakpoint next time keep_going is called? */
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int stepping_over_breakpoint;
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/* Should we step over a watchpoint next time keep_going is called?
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This is needed on targets with non-continuable, non-steppable
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watchpoints. */
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int stepping_over_watchpoint;
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/* Set to TRUE if we should finish single-stepping over a breakpoint
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after hitting the current step-resume breakpoint. The context here
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is that GDB is to do `next' or `step' while signal arrives.
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When stepping over a breakpoint and signal arrives, GDB will attempt
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to skip signal handler, so it inserts a step_resume_breakpoint at the
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signal return address, and resume inferior.
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step_after_step_resume_breakpoint is set to TRUE at this moment in
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order to keep GDB in mind that there is still a breakpoint to step over
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when GDB gets back SIGTRAP from step_resume_breakpoint. */
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int step_after_step_resume_breakpoint;
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/* Per-thread command support. */
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/* Pointer to what is left to do for an execution command after the
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target stops. Used only in asynchronous mode, by targets that
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support async execution. Several execution commands use it. */
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struct continuation *continuations;
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/* Similar to the above, but used when a single execution command
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requires several resume/stop iterations. Used by the step
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command. */
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struct continuation *intermediate_continuations;
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/* If stepping, nonzero means step count is > 1 so don't print frame
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next time inferior stops if it stops due to stepping. */
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int step_multi;
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/* This is used to remember when a fork or vfork event was caught by
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a catchpoint, and thus the event is to be followed at the next
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resume of the thread, and not immediately. */
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struct target_waitstatus pending_follow;
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/* True if this thread has been explicitly requested to stop. */
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int stop_requested;
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/* The initiating frame of a nexting operation, used for deciding
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which exceptions to intercept. If it is null_frame_id no
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bp_longjmp or bp_exception but longjmp has been caught just for
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bp_longjmp_call_dummy. */
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struct frame_id initiating_frame;
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/* Private data used by the target vector implementation. */
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struct private_thread_info *private;
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/* Function that is called to free PRIVATE. If this is NULL, then
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xfree will be called on PRIVATE. */
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void (*private_dtor) (struct private_thread_info *);
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/* Branch trace information for this thread. */
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struct btrace_thread_info btrace;
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};
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/* Create an empty thread list, or empty the existing one. */
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extern void init_thread_list (void);
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/* Add a thread to the thread list, print a message
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that a new thread is found, and return the pointer to
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the new thread. Caller my use this pointer to
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initialize the private thread data. */
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extern struct thread_info *add_thread (ptid_t ptid);
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/* Same as add_thread, but does not print a message
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about new thread. */
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extern struct thread_info *add_thread_silent (ptid_t ptid);
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/* Same as add_thread, and sets the private info. */
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extern struct thread_info *add_thread_with_info (ptid_t ptid,
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struct private_thread_info *);
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/* Delete an existing thread list entry. */
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extern void delete_thread (ptid_t);
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/* Delete an existing thread list entry, and be quiet about it. Used
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after the process this thread having belonged to having already
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exited, for example. */
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extern void delete_thread_silent (ptid_t);
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/* Delete a step_resume_breakpoint from the thread database. */
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extern void delete_step_resume_breakpoint (struct thread_info *);
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/* Delete an exception_resume_breakpoint from the thread database. */
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extern void delete_exception_resume_breakpoint (struct thread_info *);
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/* Delete the single-step breakpoints of thread TP, if any. */
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extern void delete_single_step_breakpoints (struct thread_info *tp);
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/* Check if the thread has software single stepping breakpoints
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set. */
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extern int thread_has_single_step_breakpoints_set (struct thread_info *tp);
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/* Check whether the thread has software single stepping breakpoints
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set at PC. */
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extern int thread_has_single_step_breakpoint_here (struct thread_info *tp,
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struct address_space *aspace,
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CORE_ADDR addr);
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/* Translate the integer thread id (GDB's homegrown id, not the system's)
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into a "pid" (which may be overloaded with extra thread information). */
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extern ptid_t thread_id_to_pid (int);
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/* Translate a 'pid' (which may be overloaded with extra thread information)
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into the integer thread id (GDB's homegrown id, not the system's). */
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extern int pid_to_thread_id (ptid_t ptid);
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/* Boolean test for an already-known pid (which may be overloaded with
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extra thread information). */
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extern int in_thread_list (ptid_t ptid);
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/* Boolean test for an already-known thread id (GDB's homegrown id,
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not the system's). */
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extern int valid_thread_id (int thread);
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/* Search function to lookup a thread by 'pid'. */
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extern struct thread_info *find_thread_ptid (ptid_t ptid);
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/* Find thread by GDB user-visible thread number. */
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struct thread_info *find_thread_id (int num);
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/* Finds the first thread of the inferior given by PID. If PID is -1,
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returns the first thread in the list. */
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struct thread_info *first_thread_of_process (int pid);
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/* Returns any thread of process PID, giving preference to the current
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thread. */
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extern struct thread_info *any_thread_of_process (int pid);
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/* Returns any non-exited thread of process PID, giving preference to
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the current thread, and to not executing threads. */
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extern struct thread_info *any_live_thread_of_process (int pid);
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/* Change the ptid of thread OLD_PTID to NEW_PTID. */
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void thread_change_ptid (ptid_t old_ptid, ptid_t new_ptid);
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/* Iterator function to call a user-provided callback function
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once for each known thread. */
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typedef int (*thread_callback_func) (struct thread_info *, void *);
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extern struct thread_info *iterate_over_threads (thread_callback_func, void *);
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/* Traverse all threads, except those that have THREAD_EXITED
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state. */
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#define ALL_NON_EXITED_THREADS(T) \
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for (T = thread_list; T; T = T->next) \
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if ((T)->state != THREAD_EXITED)
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/* Like ALL_NON_EXITED_THREADS, but allows deleting the currently
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iterated thread. */
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#define ALL_NON_EXITED_THREADS_SAFE(T, TMP) \
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for ((T) = thread_list; \
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(T) != NULL ? ((TMP) = (T)->next, 1): 0; \
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(T) = (TMP)) \
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if ((T)->state != THREAD_EXITED)
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extern int thread_count (void);
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/* Switch from one thread to another. */
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extern void switch_to_thread (ptid_t ptid);
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/* Marks thread PTID is running, or stopped.
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If PTID is minus_one_ptid, marks all threads. */
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extern void set_running (ptid_t ptid, int running);
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/* Marks or clears thread(s) PTID as having been requested to stop.
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If PTID is MINUS_ONE_PTID, applies to all threads. If
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ptid_is_pid(PTID) is true, applies to all threads of the process
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pointed at by PTID. If STOP, then the THREAD_STOP_REQUESTED
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observer is called with PTID as argument. */
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extern void set_stop_requested (ptid_t ptid, int stop);
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/* NOTE: Since the thread state is not a boolean, most times, you do
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not want to check it with negation. If you really want to check if
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the thread is stopped,
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use (good):
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if (is_stopped (ptid))
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instead of (bad):
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if (!is_running (ptid))
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The latter also returns true on exited threads, most likelly not
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what you want. */
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/* Reports if in the frontend's perpective, thread PTID is running. */
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extern int is_running (ptid_t ptid);
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/* Is this thread listed, but known to have exited? We keep it listed
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(but not visible) until it's safe to delete. */
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extern int is_exited (ptid_t ptid);
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/* In the frontend's perpective, is this thread stopped? */
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extern int is_stopped (ptid_t ptid);
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/* Marks thread PTID as executing, or not. If PTID is minus_one_ptid,
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marks all threads.
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Note that this is different from the running state. See the
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description of state and executing fields of struct
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thread_info. */
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extern void set_executing (ptid_t ptid, int executing);
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/* Reports if thread PTID is executing. */
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extern int is_executing (ptid_t ptid);
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/* True if any (known or unknown) thread is or may be executing. */
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extern int threads_are_executing (void);
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/* Merge the executing property of thread PTID over to its thread
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state property (frontend running/stopped view).
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"not executing" -> "stopped"
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"executing" -> "running"
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"exited" -> "exited"
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If PTID is minus_one_ptid, go over all threads.
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Notifications are only emitted if the thread state did change. */
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extern void finish_thread_state (ptid_t ptid);
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/* Same as FINISH_THREAD_STATE, but with an interface suitable to be
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registered as a cleanup. PTID_P points to the ptid_t that is
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passed to FINISH_THREAD_STATE. */
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extern void finish_thread_state_cleanup (void *ptid_p);
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/* Commands with a prefix of `thread'. */
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extern struct cmd_list_element *thread_cmd_list;
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/* Print notices on thread events (attach, detach, etc.), set with
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`set print thread-events'. */
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extern int print_thread_events;
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extern void print_thread_info (struct ui_out *uiout, char *threads,
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int pid);
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extern struct cleanup *make_cleanup_restore_current_thread (void);
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/* Returns a pointer into the thread_info corresponding to
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INFERIOR_PTID. INFERIOR_PTID *must* be in the thread list. */
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extern struct thread_info* inferior_thread (void);
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extern void update_thread_list (void);
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/* Delete any thread the target says is no longer alive. */
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extern void prune_threads (void);
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/* Return true if PC is in the stepping range of THREAD. */
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int pc_in_thread_step_range (CORE_ADDR pc, struct thread_info *thread);
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extern struct thread_info *thread_list;
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#endif /* GDBTHREAD_H */
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