Messages in this thread | | | Date | Tue, 5 Nov 2013 17:28:20 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6) |
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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.
> This is more complex situation and needs more discussion > as you said. So let's skip the discussion for now. :)
Agreed.
> > 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.
> >> > Can't we simply implement get_user_vaddr() as > >> > > >> > static void __user *get_user_vaddr(unsigned long addr, struct trace_uprobe *tu) > >> > { > >> > void __user *vaddr = (void __force __user *)addr; > >> > > >> > /* A NULL tu means that we already got the vaddr */ > >> > if (tu) > >> > vaddr += (current->mm->start_data & PAGE_MASK); > >> > > >> > return vaddr; > >> > } > >> > > >> This can only work with the probes fetching data from the executable, > >> right? But as I said it should support any other binaries too. > > > > See above, we can't in general read other binaries. > > Okay, I need to clarify my words. I'm not saying about "cross-fetch" > here, what I wanted to say is adding a probe in some dso and fetch data > from the dso. > > [...snip...]
Yes, sorry for confusion, see above.
Oleg.
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