[Bug uprobes/5079] runtime/uprobes: stap module exit w/ outstanding uretprobe_instances

["jkenisto at us dot ibm dot com" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From jkenisto at us dot ibm dot com  2007-10-02 18:31 -------
Here's a proposed design for modifying stap to optionally build
and use a uprobes module whose source resides in runtime/uprobes.

Currently, runtime/uprobes contains code that is included
directly into the stap-generated module.  This suffers from
problems, as reported in this bugzilla.  It will be modified
to be built as a kernel module that staprun can insert, as
needed, before inserting the stap-generated module.

If stap emits calls to the uprobes API, it will also attempt to
build uprobes as a module, using the source and (new) Makefile
in runtime/uprobes.  Stap will also pass the -u ("uprobes") flag
to staprun.

To account for the possibility of uprobes being part of the kernel
build (either as a module or as a built-in component), stap will
generate code that looks something like:

#if defined(CONFIG_UPROBES) || defined(CONFIG_UPROBES_MODULE)
#include <linux/uprobes.h>
#else
#include "uprobes/uprobes.h"
#endif

When passed the -u flag, staprun will check to see whether (say)
unregister_uprobe already shows up in /proc/kallsyms.  If it doesn't,
staprun will try the following before loading the SystemTap-generated
module:
1. modprobe uprobes
2. Load uprobes.ko from runtime/uprobes.
Seems like we have to do #1 first because of the way the above
#includes work.  If the user wants to use the stap-runtime version
of uprobes.ko instead of the version in /lib/modules, then I
guess he/she should copy the stap-runtime version into
/lib/modules.

Questions:
- Should we avoid the make if (say) unregister_uprobe already shows
up in /proc/kallsyms?  What would be the implications for a "stap now,
staprun later" scenario?
- Should we avoid using /lib/modules/.../uprobes.ko, and instead
use only the stap runtime version?  If so, we'd take the
"defined(CONFIG_UPROBES_MODULE)" clause out of the above code;
and we'd skip the modprobe.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dsmith at redhat dot com,
                   |                            |hunt at redhat dot com, fche
                   |                            |at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=5079

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