Re: [PATCH] objtool: fix build of 64-bit kernel with 32-bit userspace

[Mikulas Patocka]

On Tue, 7 Nov 2017, Josh Poimboeuf wrote:

> > Is there some technical reason why do you want to avoid 
> > CONFIG_GUESS_UNWINDER?
> 
> The technical reason for avoiding the guess unwinder is that it's
> sketchy: it gives false positive results.

I've always used kernels without frame pointer and I don't see any problem 
with decoding stack traces with some phantom entries that were left in the 
stack - it's easy to find out which functions could call which functions 
and discard the phantom entries.

> Not only for oopses, but for all the other users of the unwinder: 
> /proc/<pid>/stack, perf, lockdep, etc.  So it's a correctness issue.

Experts need these features, but casual users don't.

> I agree with you that the frame pointer unwinder has drawbacks, but if
> somebody cares about those drawbacks, I would consider that person an
> "expert" ;-)

The Kconfig entry says that frame pointers degrade performance by 5-10% - 
so almost any user would care about it, not just experts.

Mikulas