# Re: \[PATCH 23/33\] x86/asm/bpf: Create stack frames in bpf\_jit.S

- From: Ingo Molnar \<mingo@kernel.org\>
- Date: 2016-01-22 07:36:55 
- List: netdev
- Page: https://ratatoskr.run/netdev/2016/01/4665999
- Thread: https://ratatoskr.run/netdev/2016/01/4665783/t.md

```text

* Alexei Starovoitov [ref] wrote:

> > > I could be missing something. I think either this patch is not need or you 
> > > need to teach the tool to ignore all JITed stuff. I don't think it's 
> > > practical to annotate everything. Different JITs do their own magic. s390 
> > > JIT is even more fancy.
> > 
> > Well, but the point of these patches isn't to make the tool happy.  It's 
> > really to make sure that runtime stack traces can be made reliable. Maybe I'm 
> > missing something but I don't see why JIT code can't honor 
> > CONFIG_FRAME_POINTER just like any other code.
> 
> It can if there is no performance cost added. I can speak for x64 JIT, but the 
> rest needs to be analyzed as well. My point was that may be it's easier to 
> ignore all JITed code and just say that such call stacks may be unreliable? 
> live-patching is not applicable to JITed code anyway or you want to livepatch 
> the callees of it?

So the rule is that if frame pointers are enabled all kernel code should have 
correct stack frames - in case an IRQ (or NMI) hits it or it crashes.

Thanks,

	Ingo
```