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authorPedro Alves <palves@redhat.com>2015-03-03 01:25:17 +0000
committerPedro Alves <palves@redhat.com>2015-03-03 01:25:17 +0000
commit95e50b2723eba05ca34e9ea69c1de63e65ce9578 (patch)
treec8d908ad51dd6778c1a87d74d05be7d20a3db4a6 /gdb/infrun.c
parentcfe6bf439228831f7bddb8160fb099d0e16215a6 (diff)
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follow-exec: delete all non-execing threads
This fixes invalid reads Valgrind first caught when debugging against a GDBserver patched with a series that adds exec events to the remote protocol. Like these, using the gdb.threads/thread-execl.exp test: $ valgrind ./gdb -data-directory=data-directory ./testsuite/gdb.threads/thread-execl -ex "tar extended-remote :9999" -ex "b thread_execler" -ex "c" -ex "set scheduler-locking on" ... Breakpoint 1, thread_execler (arg=0x0) at src/gdb/testsuite/gdb.threads/thread-execl.c:29 29 if (execl (image, image, NULL) == -1) (gdb) n Thread 32509.32509 is executing new program: build/gdb/testsuite/gdb.threads/thread-execl [New Thread 32509.32532] ==32510== Invalid read of size 4 ==32510== at 0x5AA7D8: delete_breakpoint (breakpoint.c:13989) ==32510== by 0x6285D3: delete_thread_breakpoint (thread.c:100) ==32510== by 0x628603: delete_step_resume_breakpoint (thread.c:109) ==32510== by 0x61622B: delete_thread_infrun_breakpoints (infrun.c:2928) ==32510== by 0x6162EF: for_each_just_stopped_thread (infrun.c:2958) ==32510== by 0x616311: delete_just_stopped_threads_infrun_breakpoints (infrun.c:2969) ==32510== by 0x616C96: fetch_inferior_event (infrun.c:3267) ==32510== by 0x63A2DE: inferior_event_handler (inf-loop.c:57) ==32510== by 0x4E0E56: remote_async_serial_handler (remote.c:11877) ==32510== by 0x4AF620: run_async_handler_and_reschedule (ser-base.c:137) ==32510== by 0x4AF6F0: fd_event (ser-base.c:182) ==32510== by 0x63806D: handle_file_event (event-loop.c:762) ==32510== Address 0xcf333e0 is 16 bytes inside a block of size 200 free'd ==32510== at 0x4A07577: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==32510== by 0x77CB74: xfree (common-utils.c:98) ==32510== by 0x5AA954: delete_breakpoint (breakpoint.c:14056) ==32510== by 0x5988BD: update_breakpoints_after_exec (breakpoint.c:3765) ==32510== by 0x61360F: follow_exec (infrun.c:1091) ==32510== by 0x6186FA: handle_inferior_event (infrun.c:4061) ==32510== by 0x616C55: fetch_inferior_event (infrun.c:3261) ==32510== by 0x63A2DE: inferior_event_handler (inf-loop.c:57) ==32510== by 0x4E0E56: remote_async_serial_handler (remote.c:11877) ==32510== by 0x4AF620: run_async_handler_and_reschedule (ser-base.c:137) ==32510== by 0x4AF6F0: fd_event (ser-base.c:182) ==32510== by 0x63806D: handle_file_event (event-loop.c:762) ==32510== [Switching to Thread 32509.32532] Breakpoint 1, thread_execler (arg=0x0) at src/gdb/testsuite/gdb.threads/thread-execl.c:29 29 if (execl (image, image, NULL) == -1) (gdb) The breakpoint in question is the step-resume breakpoint of the non-main thread, the one that was "next"ed. The exact same issue can be seen on mainline with native debugging, by running the thread-execl.exp test in non-stop mode, because the kernel doesn't report a thread exit event for the execing thread. Tested on x86_64 Fedora 20. gdb/ChangeLog: 2015-03-02 Pedro Alves <palves@redhat.com> * infrun.c (follow_exec): Delete all threads of the process except the event thread. Extended comments. gdb/testsuite/ChangeLog: 2015-03-02 Pedro Alves <palves@redhat.com> * gdb.threads/thread-execl.exp (do_test): Handle non-stop. (top level): Call do_test with non-stop as well.
Diffstat (limited to 'gdb/infrun.c')
-rw-r--r--gdb/infrun.c48
1 files changed, 36 insertions, 12 deletions
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 15589b6..f87ed4c 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1060,10 +1060,11 @@ show_follow_exec_mode_string (struct ui_file *file, int from_tty,
/* EXECD_PATHNAME is assumed to be non-NULL. */
static void
-follow_exec (ptid_t pid, char *execd_pathname)
+follow_exec (ptid_t ptid, char *execd_pathname)
{
- struct thread_info *th = inferior_thread ();
+ struct thread_info *th, *tmp;
struct inferior *inf = current_inferior ();
+ int pid = ptid_get_pid (ptid);
/* This is an exec event that we actually wish to pay attention to.
Refresh our symbol table to the newly exec'd program, remove any
@@ -1088,24 +1089,47 @@ follow_exec (ptid_t pid, char *execd_pathname)
mark_breakpoints_out ();
- update_breakpoints_after_exec ();
-
- /* If there was one, it's gone now. We cannot truly step-to-next
- statement through an exec(). */
+ /* The target reports the exec event to the main thread, even if
+ some other thread does the exec, and even if the main thread was
+ stopped or already gone. We may still have non-leader threads of
+ the process on our list. E.g., on targets that don't have thread
+ exit events (like remote); or on native Linux in non-stop mode if
+ there were only two threads in the inferior and the non-leader
+ one is the one that execs (and nothing forces an update of the
+ thread list up to here). When debugging remotely, it's best to
+ avoid extra traffic, when possible, so avoid syncing the thread
+ list with the target, and instead go ahead and delete all threads
+ of the process but one that reported the event. Note this must
+ be done before calling update_breakpoints_after_exec, as
+ otherwise clearing the threads' resources would reference stale
+ thread breakpoints -- it may have been one of these threads that
+ stepped across the exec. We could just clear their stepping
+ states, but as long as we're iterating, might as well delete
+ them. Deleting them now rather than at the next user-visible
+ stop provides a nicer sequence of events for user and MI
+ notifications. */
+ ALL_NON_EXITED_THREADS_SAFE (th, tmp)
+ if (ptid_get_pid (th->ptid) == pid && !ptid_equal (th->ptid, ptid))
+ delete_thread (th->ptid);
+
+ /* We also need to clear any left over stale state for the
+ leader/event thread. E.g., if there was any step-resume
+ breakpoint or similar, it's gone now. We cannot truly
+ step-to-next statement through an exec(). */
+ th = inferior_thread ();
th->control.step_resume_breakpoint = NULL;
th->control.exception_resume_breakpoint = NULL;
th->control.single_step_breakpoints = NULL;
th->control.step_range_start = 0;
th->control.step_range_end = 0;
- /* The target reports the exec event to the main thread, even if
- some other thread does the exec, and even if the main thread was
- already stopped --- if debugging in non-stop mode, it's possible
- the user had the main thread held stopped in the previous image
- --- release it now. This is the same behavior as step-over-exec
- with scheduler-locking on in all-stop mode. */
+ /* The user may have had the main thread held stopped in the
+ previous image (e.g., schedlock on, or non-stop). Release
+ it now. */
th->stop_requested = 0;
+ update_breakpoints_after_exec ();
+
/* What is this a.out's name? */
printf_unfiltered (_("%s is executing new program: %s\n"),
target_pid_to_str (inferior_ptid),