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.
That said, I have a working patch I was planning to post today that
introduces the KPROBE_ADDR macro that abstracts out the architecture-specific
artefacts of getting the actual text address to probe, so kprobe modules
can be made more portable. I was envisaging this to be used by the module
writer, but with your idea, this could live in-kernel itself.
I'll cook up a patch for this in a short while.
Ananth
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