ttrace.2 (2010 09)

t
ttrace(2) ttrace(2)
Events
As noted earlier, a tracing process can set event flags in the context of a traced process, or its individual
threads, to cause the threads to respond to specific events during their execution. When an event flag is
set in the context of the process, all threads in the process respond to the event. When set in the context
of a thread, only the specific thread will respond to the event.
Important
If an event is requested by the process, the event mask of the thread is not examined. For the event mask
of the thread to be significant, the process event must be be unset. Similarly, if an event option is enabled
in the process, the option for the thread is not considered. Event masks may be inherited across
fork()
using the tte_opts options in the ttevent_t
structure. If TTEO_PROC_INHERIT
is set, the child
process inherits the event mask of its parent. If
TTEO_LWP_INHERIT
is set, the lwp inherits the event
mask of the lwp that invoked
fork(). If the latter is set, the lwp created by
lwp_create() also
inherits the event mask of the creating thread.
These events are:
TTEVT_SIGNAL This event flag indicates that the traced thread needs to examine signal mask bits
when processing signals. This means that, by default, threads stop when receiving a
signal. If the signal being processed has its mask bit set, signal processing continues
as though the process were not traced: the traced thread is not stopped, and the trac-
ing process is not notified of the signal. On the other hand, if the signal mask bit is
not set for the signal being processed, the traced thread is stopped and the tracing
process is notified via ttrace_wait()
.
Note that the SIGKILL signal can never be unmasked. It behaves as though its mask
bit were always set. This means that a SIGKILL signal cannot be used to stop a
traced thread. The SIGTRAP signal is also special in that it is used to stop traced
threads when they respond to a trap, such as a breakpoint or a single step. Conse-
quently, masking SIGTRAP, even though allowed, will result in unexpected behavior
in these conditions.
TTEVT_FORK This event flag indicates that the traced thread needs to take special action when it
invokes fork(). When set, both the parent thread and the initial thread in the child
process stop (after the child process is marked as a traced process and adopts its
parent’s debugger). Both threads log the fact that they stopped in response to a
TTEVT_FORK event. The parent thread provides the pid of the child process in the
appropriate portion of the ttstate_t structure. The initial thread of the child pro-
cess provides the pid of the parent in the same location. See the ttstate_t struc-
ture description for further details.
TTEVT_VFORK This event flag indicates that the traced thread needs to take special action when it
invokes vfork(). The behavior is identical to that of TTEVT_FORK but it is impor-
tant to note that the caveats with respect to vfork(), continue to apply here. In
particular, it needs to be remembered that when the child process stops, its parent is
asleep, and that the child borrows the parent’s address space until a call to exec()
or an exit (either by a call to exit() or abnormally) takes place. Continuing the
parent process before the above steps take place results in an error.
TTEVT_PREFORK This event flag indicates that the traced thread needs to notify the debugger, during a
fork() or vfork() operation, just after the child process ID and thread ID is
known and before the child process is created and set to run. The parent thread is
stopped and it provides the pid of the child process and lwpid of the child’s initial
thread.
Note: Upon continuation from this event, the traced thread does not guarantee that
the child process with an earlier returned pid and lwpid can be created since the
fork() or vfork() operation might fail.
TTEVT_FORK_FAIL
This event flag indicates that the traced thread needs to notify the debugger upon the
failure of a fork() or vfork() operation. The traced parent thread is stopped and
returns the error code for fork failure.
TTEVT_EXEC This event flag indicates that a traced thread needs to notify the debugger upon com-
pletion of loading the new executable file, in the exec() system call. The length of
the pathname string (not including a null terminating character) is returned in the
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