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Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf)

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf)
Date 2017-07-12 10:30 +0200
Message-ID <u2lbX-5M9-1@gated-at.bofh.it> (permalink)
References <u25qx-454-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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* Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> The biggest change is that undwarf was renamed to ORC.  Here's the
> relevant explanation from the docs:
> 
>   Etymology
>   ---------
>   
>   Orcs, fearsome creatures of medieval folklore, are the Dwarves' natural
>   enemies.  Similarly, the ORC unwinder was created in opposition to the
>   complexity and slowness of DWARF.
>   
>   "Although Orcs rarely consider multiple solutions to a problem, they do
>   excel at getting things done because they are creatures of action, not
>   thought." [3]  Similarly, unlike the esoteric DWARF unwinder, the
>   veracious ORC unwinder wastes no time or siloconic effort decoding
>   variable-length zero-extended unsigned-integer byte-coded
>   state-machine-based debug information entries.
>   
>   Similar to how Orcs frequently unravel the well-intentioned plans of
>   their adversaries, the ORC unwinder frequently unravels stacks with
>   brutal, unyielding efficiency.
>   
>   ORC stands for Oops Rewind Capability.

Perfect naming!

(ORC might also stand for "Optimized Rewind Capability".)

> Create a new "ORC" unwinder, enabled by CONFIG_ORC_UNWINDER, and plug it
> into the x86 unwinder framework.  Objtool is used to generate the ORC
> debuginfo.  The ORC debuginfo format is basically a simplified version
> of DWARF CFI.  More details below.

BTW., we should perhaps consolidate our unwinder related Kconfig space, 
hierarchically:

	CONFIG_UNWINDER
	CONFIG_UNWINDER_ORC
	CONFIG_UNWINDER_FRAME_POINTERS

Note that as a side effect it would be a valid small systems build option to have 
no unwinder at all, if CONFIG_EXPERT=y is set and such: !CONFIG_UNWINDER=n would 
be a sibling to !CONFIG_BUG.

CONFIG_FRAME_POINTERS et al would be left for architectures where it has a meaning 
beyond backtrace generation. (Not sure whether there's any such architectures.)

> The unwinder works well in my testing.  It unwinds through interrupts,
> exceptions, and preemption, with and without frame pointers, across
> aligned stacks and dynamically allocated stacks.  If something goes
> wrong during an oops, it successfully falls back to printing the '?'
> entries just like the frame pointer unwinder.

Ok, I'll start applying your patches after -rc1, unless anyone objects.

> The ORC data format does have a few downsides compared to DWARF.  The
> ORC unwind tables take up ~1MB more memory than DWARF eh_frame tables.

Could we also write this in percentage, not absolute RAM size - i.e. ORC unwind 
tables take 30% more RAM (+0.7 MB on an x86 defconfig kernel) than DWARF eh_frame 
tables.

Thanks,

	Ingo

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Thread

[PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-11 17:40 +0200
  Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Ingo Molnar <mingo@kernel.org> - 2017-07-12 10:30 +0200
    Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-12 16:50 +0200
      Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Ingo Molnar <mingo@kernel.org> - 2017-07-12 21:30 +0200
        Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-14 19:20 +0200
  Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andres Freund <andres@anarazel.de> - 2017-07-12 23:50 +0200
    Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 00:40 +0200
      Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andres Freund <andres@anarazel.de> - 2017-07-13 00:40 +0200
        Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 00:50 +0200
          Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andres Freund <andres@anarazel.de> - 2017-07-13 01:00 +0200
      Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Peter Zijlstra <peterz@infradead.org> - 2017-07-13 09:20 +0200
        Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Peter Zijlstra <peterz@infradead.org> - 2017-07-13 11:00 +0200
          Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Ingo Molnar <mingo@kernel.org> - 2017-07-13 11:20 +0200
            Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 14:20 +0200
              Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 14:30 +0200
                Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 14:40 +0200
                Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Ingo Molnar <mingo@kernel.org> - 2017-07-14 10:40 +0200
              Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Ingo Molnar <mingo@kernel.org> - 2017-07-14 10:30 +0200
        Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Peter Zijlstra <peterz@infradead.org> - 2017-07-13 11:00 +0200
  Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andi Kleen <andi@firstfloor.org> - 2017-07-13 00:40 +0200
    Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 00:50 +0200
      Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andi Kleen <andi@firstfloor.org> - 2017-07-13 06:30 +0200
        Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 15:20 +0200
      Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Ingo Molnar <mingo@kernel.org> - 2017-07-13 11:30 +0200
    Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andy Lutomirski <luto@kernel.org> - 2017-07-13 01:30 +0200
    Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Mike Galbraith <efault@gmx.de> - 2017-07-13 05:10 +0200
      Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andi Kleen <andi@firstfloor.org> - 2017-07-13 06:20 +0200
        Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Mike Galbraith <efault@gmx.de> - 2017-07-13 06:40 +0200
          Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Andi Kleen <andi@firstfloor.org> - 2017-07-13 06:50 +0200
            Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Mike Galbraith <efault@gmx.de> - 2017-07-13 07:30 +0200
            Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) Jiri Kosina <jikos@kernel.org> - 2017-07-13 14:10 +0200

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