Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)

[Namhyung Kim <namhyung@kernel.org>]

Hi Oleg,

On Tue, 5 Nov 2013 17:28:20 +0100, Oleg Nesterov wrote:
> On 11/05, Namhyung Kim wrote:
>>
>> On Mon, 4 Nov 2013 16:01:12 +0100, Oleg Nesterov wrote:
>> > Or the syntax should be "name=probe @file/addr" or something like this.
>>
>> Okay.  Let's call this kind of thing "cross-fetch" (or a better name can
>> be suggested).
>
> Yes ;) and I am afraid there was some confusion in our discussion.
> I probably confused "probe other binaries" with cross-fetch and vice
> versa sometimes.

Sorry for not being clear enough.

>
>> > So far I think that trace_uprobes.c should not play games with vma. At all.
>>
>> Yes, playing with vma is fragile.  But otherwise how can we get the
>> address from the file+offset in random processes?
>
> Yes, this is not as simple as I thought.
>
> Let me repeat, somehow I completely forgot we need to probe other (libc)
> binaries (not only the executable itself) and dump the data from that
> binary. That is why I wrongly thought that that ->start_data trick can
> work.
>
> OK, I see other emails from you. Perhaps we can rely on instruction_pointer(),
> (I'll write more emails on this), But if not, then we probably need tu->inode
> and vma games in fetch/get_user_vaddr(). I'd still like to avoid this, if
> possible, but I am no longer sure.

Yes, I think it'll be necessary for the cross-fetch anyway.

Thanks,
Namhyung