* Josh Poimboeuf <jpoimboe@xxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
