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SubjectRe: [RFC 0/5] kernel: backtrace unwind support
Em Fri, Feb 10, 2012 at 10:59:51AM -0800, Linus Torvalds escreveu:
> On Fri, Feb 10, 2012 at 9:43 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> >
> > So I CC'ed Linus who has a strong here, jejb since he's the one that
> > told me several time there's a number of literate dwarfs already in the
> > kernel and Jan because I think it was him that tried last on x86.
>
> I never *ever* want to see this code ever again.
>
> Sorry, but last time was too f*cking painful. The whole (and *only*)
> point of unwinders is to make debugging easy when a bug occurs. But
> the f*cking dwarf unwinder had bugs itself, or our dwarf information
> had bugs, and in either case it actually turned several "trivial" bugs
> into a total undebuggable hell.
>
> It was made doubly painful by the developers involved then several
> times ignoring the problem, and claiming the code was bug-free when it
> clearly wasn't, or trying to claim that the problem was that we set up
> some random dwarf information wrong, when THAT GOES WITHOUT SAYING
> (since dwarf is a complex mess that never gets any actual testing
> except when things go wrong - at which point the code had better work
> regardless of whether the dwarf info was correct or not).
>
> So no. An unwinder that is several hundred lines long is simply not
> even *remotely* interesting to me.
>
> If you can mathematically prove that the unwinder is correct - even in
> the presence of bogus and actively incorrect unwinding information -
> and never ever follows a bad pointer, I'll reconsider.
>
> In the absence of that, just follow the damn chain on the stack
> *without* the "smarts" of an inevitably buggy piece of crap.

"Vote for --fno-omit-frame-pointer! One register is a cheap price to pay
for not going insane!"

/me goes back to non political things.

- Arnaldo


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