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Linux: No need to set ptrace event options in fork/clone children.

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Oleg Nesterov told me that the Linux kernel copies the parent's ptrace
options to fork/clone children, so there's no need for GDB to do that
manually.

I was actually a bit surprised, since I thought the ptracer had to
always set the ptrace options itself, and GDB is indeed calling
PTRACE_SETOPTIONS for each new fork child, if it'll stay attached.

Looking at the history of that code, I found that is was actually I
who added that set-ptrace-options-in-children bit, back in
http://sourceware.org/ml/gdb-patches/2009-05/msg00656.html.  But,
honestly, I don't recall why I needed that.  I think I may have just
blindly believed it was necessary.

I then looked back at the history of all the PTRACE_SETOPTIONS code we
have, and found that gdb never did copy the ptrace options before my
patch.  But, when gdbserver learnt to use PTRACE_EVENT_CLONE, at
http://sourceware.org/ml/gdb-patches/2007-10/msg00547.html, it was
made to do 'ptrace (PTRACE_SETOPTIONS, new_pid, 0,
PTRACE_O_TRACECLONE)' for all new clones.  Hmmm.  But, GDB itself
never did that, so it can't really ever have been necessary, I
believe, otherwise GDB should have been doing it too.

(GDBserver doesn't support following forks, and so naturally doesn't
do any PTRACE_SETOPTIONS on fork children.)

So this patch removes the -I believe- unnecessary ptrace syscalls.

Tested on x86_64 Fedora 17, native/gdbserver, and on x86_64 RHEL5
native/gdbserver (Linux 2.6.18, I think a ptrace-on-utrace kernel).
No regressions.

gdb/
2013-03-22  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (linux_child_follow_fork): Don't call
	linux_enable_event_reporting.
	(linux_handle_extended_wait): Don't call
	linux_enable_event_reporting.

gdb/gdbserver/
2013-03-22  Pedro Alves  <palves@redhat.com>

	* linux-low.c (handle_extended_wait): Don't call
	linux_enable_event_reporting.
This commit is contained in:
Pedro Alves 2013-03-22 14:52:26 +00:00
parent a2213dca18
commit 3e74e146f2
4 changed files with 12 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
gdb/ChangeLog
View File

@ -1,3 +1,10 @@
2013-03-22 Pedro Alves <palves@redhat.com>
* linux-nat.c (linux_child_follow_fork): Don't call
linux_enable_event_reporting.
(linux_handle_extended_wait): Don't call
linux_enable_event_reporting.
2013-03-22 Pedro Alves <palves@redhat.com>
* hppa-hpux-tdep.c (hppa_hpux_push_dummy_code): Define INSN macro,

5
gdb/gdbserver/ChangeLog
View File

@ -1,3 +1,8 @@
2013-03-22 Pedro Alves <palves@redhat.com>
* linux-low.c (handle_extended_wait): Don't call
linux_enable_event_reporting.
2013-03-15 Tony Theodore <tonyt@logyst.com>
PR build/9098:

2
gdb/gdbserver/linux-low.c
View File

@ -468,8 +468,6 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
warning ("wait returned unexpected status 0x%x", status);
}
linux_enable_event_reporting (new_pid);
ptid = ptid_build (pid_of (event_child), new_pid, 0);
new_lwp = (struct lwp_info *) add_lwp (ptid);
add_thread (ptid, new_lwp);

4
gdb/linux-nat.c
View File

@ -643,9 +643,6 @@ linux_child_follow_fork (struct target_ops *ops, int follow_child)
parent_pid = ptid_get_pid (inferior_ptid);
child_pid = PIDGET (inferior_thread ()->pending_follow.value.related_pid);
if (!detach_fork)
linux_enable_event_reporting (pid_to_ptid (child_pid));
if (has_vforked
&& !non_stop /* Non-stop always resumes both branches. */
&& (!target_is_async_p () || sync_execution)
@ -2316,7 +2313,6 @@ linux_handle_extended_wait (struct lwp_info *lp, int status,
this fork. We're actually doing an infcall in
linux-fork.c. */
ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
linux_enable_event_reporting (pid_to_ptid (new_pid));
/* Report the stop to the core. */
return 0;