Re: [PATCH,resubmit] Add static probes to runtime linker

[Paul Pluzhnikov <ppluzhnikov at google dot com>]

On Thu, Jul 5, 2012 at 2:33 AM, Gary Benson <gbenson@redhat.com> wrote:

+  map_complete:
+    The linker has finished removing objects into the specified
+    namespace.  The namespace's r_debug structure is consistent and
+    may be inspected.

Typo above: should be unmap_complete.

@@ -1736,7 +1739,7 @@ open_verify (const char *name, struct filebuf
*fbp, struct link_map *loader,
 	      name = strdupa (realname);
 	      free (realname);
 	    }
-	  lose (errval, fd, name, NULL, NULL, errstring, NULL);
+	  lose (errval, fd, name, NULL, NULL, errstring, NULL, 0);
 	}

Shouldn't the last parameter to lose() above be nsid?

Also, a general comment. One of the reasons the current r_debug
interface is painful is that the debugger is told: "the link_map may
have changed, go figure it out". When there are 5000 shared libraries
loaded (as is routinely the case here at Google), it takes a loooong
time for GDB to figure out whether anything in fact did change, and
exactly what. IIRC, at process startup, we get one RT_CONSISTENT for
each added DSO, and GDB re-scans the entire link_map list on each one,
resulting in quadratic behavior.

Since we are now defining a brand-new interface, it would be nice to
make it possible for the debugger to be more efficient.

Lastly, could this interface be evolved? I don't know if system tap
probes already have a mechanism for versioned interface. If they do,
great. If not, the interface should probably include version number
somewhere.


-- 
Paul Pluzhnikov