[Bug libc/2328] _dl_debug_state() RT_CONSISTENT called too early

["gbenson at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=2328

--- Comment #8 from Gary Benson <gbenson at redhat dot com> 2011-08-11 12:11:47 UTC ---
Created attachment 5895
  --> http://sourceware.org/bugzilla/attachment.cgi?id=5895
Proposed patch for Fedora

To elaborate on Jan's comment above, this is the fix we are proposing for
Fedora.  It adds a new function, _dl_debug_notify, which is called wherever
_dl_debug_state was previously called, and in a couple of other places.  For
backwards compatibility, _dl_debug_notify calls _dl_debug_state whenever it was
previously called, so applications using _dl_debug_state will see no change.
The new interface is in the form of a number of SystemTap probes in
_dl_debug_notify which applications can locate and set breakpoints on if
necessary.  The new interface has the following advantages over the existing
one:

* Applications using the new interface have much more control over the events
they are notified about.  They can set breakpoints or whatever on the probes of
interest and ignore probes that are not of interest.

* Applications using the new interface are able to be notified about other
events than the ones supported by the existing interface.  Currently there are
two new events, for the start and end of object relocation, but the interface
is extensible in the sense that new probes can be added for other events of
interest.

* Applications using the new interface can handle libraries loaded into
namespaces other than the default, eg with dlmopen.  Under the existing
interface _dl_debug_state is called but the data structure for the namespace
(with the list of loaded libraries) is unavailable.  This allows, for example,
for a fix to bug 11839.

In addition to the addition of new probes, the new interface is also extensible
in the sense that new arguments may be added to existing probes without
breaking compatibility.

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