On Mon, 23 Dec 2013 13:54:19 +0100, Mark Wielaard wrote:
> On Sun, 2013-12-22 at 16:51 +0100, Jan Kratochvil wrote:
> > If I have PID=12000 and I do 'eu-stack -p 12001' (its thread TID) then for
> > elfutils in fact PID is 12001. So if Dwfl_Thread_Callbacks.next_thread
> > returns 12001 first we can backtrace it and stop.
>
> This just shows a bug in linux-pid-attach. It doesn't properly report
> the PID (Tgid). It should only report 12001 as PID if it really is the
> thread group leader of the given TID. I'll fix that.
OK, I agree, then the situation is different. It looks a bit unusual as it is
not the behavior of GDB.
> Updated patch attached.
Fine with that with the comments below.
[...]
> --- a/libdwfl/dwfl_frame.c
> +++ b/libdwfl/dwfl_frame.c
> @@ -273,6 +273,93 @@ dwfl_getthreads (Dwfl *dwfl, int (*callback)
> (Dwfl_Thread *thread, void *arg),
> }
> INTDEF(dwfl_getthreads)
>
> +struct one_arg
> +{
> + pid_t tid;
> + bool seen;
> + int (*callback) (Dwfl_Thread *thread, void *arg);
> + void *arg;
> +};
> +
> +static int
> +get_one_thread_cb (Dwfl_Thread *thread, void *arg)
> +{
> + struct one_arg *oa = (struct one_arg *) arg;
> + if (! oa->seen && INTUSE(dwfl_thread_tid) (thread) == oa->tid)
> + {
> + oa->seen = true;
> + return oa->callback (thread, oa->arg);
Maybe it was intentionall to keep the code simple - but if oa->callback
returns DWARF_CB_OK then it will needlessly continue iterating the threads
despite it can never find that TID again.
> + }
> +
> + return DWARF_CB_OK;
> +}
> +
> +/* Note not currently exported, will be when there are more Dwfl_Thread
> + properties to query. Use dwfl_getthread_frames for now directly. */
> +static int
> +dwfl_getthread (Dwfl *dwfl, pid_t tid,
It is no longer public so I think it should not have dwfl_* prefix.
> + int (*callback) (Dwfl_Thread *thread, void *arg),
> + void *arg)
> +{
> + Dwfl_Process *process = dwfl->process;
> + if (process == NULL)
As the function is no longer public this can be rather an assert.
> + {
> + __libdwfl_seterrno (dwfl->process_attach_error);
> + return -1;
> + }
> +
> + if (process->callbacks->get_thread != NULL)
> + {
> + Dwfl_Thread thread;
> + thread.process = process;
> + thread.unwound = NULL;
> + thread.callbacks_arg = NULL;
> +
> + if (process->callbacks->get_thread (dwfl, tid, process->callbacks_arg,
> + &thread.callbacks_arg))
> + {
> + int err;
> + thread.tid = tid;
> + err = callback (&thread, arg);
> + thread_free_all_states (&thread);
> + return err;
> + }
> +
> + return -1;
> + }
> +
> + struct one_arg oa = { .tid = tid, .callback = callback,
> + .arg = arg, .seen = false };
> + int err = INTUSE(dwfl_getthreads) (dwfl, get_one_thread_cb, &oa);
> + if (err == DWARF_CB_OK && ! oa.seen)
__libdwfl_seterrno is not called.
> + return -1;
> +
> + return err;
> +}
> +
> +struct one_thread
> +{
> + int (*callback) (Dwfl_Frame *frame, void *arg);
> + void *arg;
> +};
> +
> +static int
> +get_one_thread_frames_cb (Dwfl_Thread *thread, void *arg)
> +{
> + struct one_thread *ot = (struct one_thread *) arg;
> + return INTUSE(dwfl_thread_getframes) (thread, ot->callback, ot->arg);
> +}
> +
> +int
> +dwfl_getthread_frames (Dwfl *dwfl, pid_t tid,
> + int (*callback) (Dwfl_Frame *frame, void *arg),
> + void *arg)
> +{
> + struct one_thread ot = { .callback = callback, .arg = arg };
> + return dwfl_getthread (dwfl, tid, get_one_thread_frames_cb, &ot);
> +}
> +INTDEF(dwfl_getthread_frames)
> +
> int
> dwfl_thread_getframes (Dwfl_Thread *thread,
> int (*callback) (Dwfl_Frame *state, void *arg),
> diff --git a/libdwfl/libdwfl.h b/libdwfl/libdwfl.h
> index 007089b..f1c0052 100644
> --- a/libdwfl/libdwfl.h
> +++ b/libdwfl/libdwfl.h
> @@ -662,6 +662,17 @@ typedef struct
> pid_t (*next_thread) (Dwfl *dwfl, void *dwfl_arg, void **thread_argp)
> __nonnull_attribute__ (1);
>
> + /* Called to get a specific thread. Returns true if there is a
> + thread with the given thread id number, returns false if no such
> + thread exists and may set dwfl_errno in that case. THREAD_ARGP
s/may/it will/. Setting errno has to be mandatory, not voluntary.
> + is never NULL. *THREAD_ARGP will be passed to
> + set_initial_registers or thread_detach callbacks together with
> + Dwfl_Thread *thread. This method may be NULL and will then be
> + emulated using the next_thread callback. */
> + bool (*get_thread) (Dwfl *dwfl, pid_t tid, void *dwfl_arg,
> + void **thread_argp)
> + __nonnull_attribute__ (1);
> +
> /* Called during unwinding to access memory (stack) state. Returns true
> for
> successfully read *RESULT or false and sets dwfl_errno () on failure.
> This method may be NULL - in such case dwfl_thread_getframes will return
> @@ -762,6 +773,16 @@ int dwfl_thread_getframes (Dwfl_Thread *thread,
> void *arg)
> __nonnull_attribute__ (1, 2);
>
> +/* Like dwfl_thread_getframes, but specifying the thread by its unique
> + identifier number. Returns zero if all frames have been processed
> + by the callback, returns -1 on error (and when no thread with
> + the given thread id number exists), or the value of the callback
> + when not DWARF_CB_OK. -1 returned on error will set dwfl_errno (). */
> +int dwfl_getthread_frames (Dwfl *dwfl, pid_t tid,
> + int (*callback) (Dwfl_Frame *thread, void *arg),
> + void *arg)
> + __nonnull_attribute__ (1, 3);
> +
> /* Return *PC (program counter) for thread-specific frame STATE.
> Set *ISACTIVATION according to DWARF frame "activation" definition.
> Typically you need to substract 1 from *PC if *ACTIVATION is false to
> safely
[...]
Thanks,
Jan
