Messages in this thread | | | Date | Wed, 12 Jul 2017 10:27:10 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v3 00/10] x86: ORC unwinder (previously undwarf) |
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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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