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SubjectRe: [PATCH] module interface improvement for kprobes
On Mon, Aug 07, 2006 at 10:22:13AM +0530, Ananth N Mavinakayanahalli wrote:
> On Fri, Aug 04, 2006 at 04:57:11PM +0100, Christoph Hellwig wrote:
> > > {
> > > /* grab the module, making sure it won't get unloaded until
> > > * we're done */
> > > const char *mod_name = "joydev";
> > > if (module_get_byname(mod_name, &mod) != 0)
> > > return 1;
> > >
> > > /* Specify the address/offset where you want to insert
> > > * probe. If this were a real kprobe module, we'd "relocate"
> > > * our probe address based on the load address of the module
> > > * we're interested in. */
> > > kp.addr = (kprobe_opcode_t *) mod->module_core + 0;
> > >
> > > /* All set to register with Kprobes */
> > > register_kprobe(&kp);
> > > return 0;
> > > }
> >
> > This interface is horrible. You actual patch looks good to me, but it
> > I can't see why you would need it. kallsyms_lookup_name deals with modules
> > transparently and you shouldn't put a probe at a relative offset into a
> > module but only at a symbol you could find with kallsys.
> >
> > That beeing said we should probably change the kprobes interface to
> > automatically do the kallsysms name lookup for the caller. It would simplify
> > the kprobes interface and allow us to get rid of the kallsyms_lookup_name
> > export that doesn't have a valid use except for kprobes. With
> > that change the example kprobe would look like:
>
> This sounds like a good idea. How about we still allow .addr atleast for
> users who know what they are doing and would want to just specify a text
> addr?
>
> > static struct kprobe kp = {
> .addr = <addr>
>
> > .pre_handler = handler_pre,
> > .post_handler = handler_post,
> > .fault_handler = handler_fault,
> > .symbol_name = "do_fork",
> > };
>
> The symbol_name lookup can then be done when only when .addr is non-NULL.

Duh! I meant to say lookup when .addr is NULL.

Ananth
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