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Re: [PATCH] Remove support for thread events without PTRACE_EVENT_CLONE in GDB.




On 12/10/2015 09:47 AM, Pedro Alves wrote:
On 12/09/2015 05:39 PM, Antoine Tremblay wrote:
Before, on systems that did not support PTRACE_EVENT_CLONE, both GDB and
GDBServer coordinated with libthread_db.so to insert breakpoints at magic
locations in libpthread.so, in order to break at thread creation and
thread death.

Support for thread events was removed from GDBServer as patch:
https://sourceware.org/ml/gdb-patches/2015-11/msg00466.html

This patch removes support for thread events in GDB.

No regressions found on Ubuntu 14.04 x86_64.

gdb/ChangeLog:
	* breakpoint.c (create_thread_event_breakpoint): Remove.
	(remove_thread_event_breakpoints): Remove.

That's still used:

  $ grep create_thread_event_breakpoint gdb/*
  gdb/aix-thread.c:  if (!create_thread_event_breakpoint (target_gdbarch (), pd_brk_addr))



Ouch, I had missed that one. I'll re-add the function.

Also I noticed I forgot to remove the declaration in breakpoint.h I'll fix that for remove_thread_event_breakpoint.


-  /* Under GNU/Linux, we have to attach to each and every thread.  */
-  if (target_has_execution
-      && tp == NULL)
-    {
-      int res;
-
-      res = lin_lwp_attach_lwp (ptid_build (ptid_get_pid (ptid),
-					    ti_p->ti_lid, 0));
-      if (res < 0)
-	{
-	  /* Error, stop iterating.  */


Is lin_lwp_attach_lwp used anywhere after this?


No indeed, Removing.



@@ -1592,24 +1200,10 @@ find_new_threads_callback (const td_thrhandle_t *th_p, void *data)

    if (ti.ti_tid == 0)
      {
-      /* A thread ID of zero means that this is the main thread, but
-	 glibc has not yet initialized thread-local storage and the
-	 pthread library.  We do not know what the thread's TID will
-	 be yet.  Just enable event reporting and otherwise ignore
-	 it.  */

You shouldn't remove the whole comment -- it's still all correct
except the last sentence.


Yes I hesitated on that one, it felt like the reason for the comment was the last sentence so I removed it.

But I'm OK with leaving it there.

V2 follows in next mail.

Thanks,
Antoine


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