LWN: Comments on "The ORCs are coming"

The ORCs are coming

johill — Thu, 14 Sep 2017 07:09:14 +0000

Now that this is merged ...

What happens if we crash in eBPF JIT'ed code? Clearly there cannot be any ORC annotation for that? I'm not sure the JIT ever emits stack usage though.

Is objtool for x86_64 only?

ajdlinux — Thu, 14 Sep 2017 03:54:14 +0000

ARM people feel neglected? I work exclusively on powerpc! :P

From what I can tell of the initially-x86-only features that do get ported to other architectures, arm/arm64 gets them first, powerpc can be (an often distant) second, and everything else may well be never...

ARMing ORCs

vomlehn — Thu, 07 Sep 2017 19:46:26 +0000

Nice. Having done truly shameful things to get MIPS stack backtraces, I spent some time on an approach like this but changed jobs and it fell out of my universe. I have, apparently, a stack backtrace fetish and would take on the ARM version if I could just clone myself. Sigh.

The ORCs are coming

vineetg — Sun, 06 Aug 2017 15:08:44 +0000

Is this x86 specific or can this be adapted to all arches ?

Is objtool for x86_64 only?

Wol — Thu, 03 Aug 2017 09:50:32 +0000

Ring the hobbits, maybe?

Cheers,
Wol

The ORCs are coming

vbabka — Tue, 01 Aug 2017 14:32:27 +0000

Matt Fleming yesterday also posted a blog post about ORC unwinder, with some more details for some aspects of the topic: http://www.codeblueprint.co.uk/2017/07/31/the-orc-unwinde...

Is objtool for x86_64 only?

nix — Tue, 01 Aug 2017 13:38:26 +0000

ARMing ORCs seems distinctly dangerous to me: they are not renowned for friendliness as neighbours. However, in this case the ARMs have already taken over the world so I'm not sure there's much the ORCs could do. :P

Is objtool for x86_64 only?

corbet — Tue, 01 Aug 2017 12:24:08 +0000

Lots of kernel features show up on x86 first; it doesn't usually take all that long for the interesting ones to spread to the other architectures. I don't know of anybody working on ARMing the ORCs at the moment, but it would not surprise me if it happened fairly soon once the x86 stuff lands.

Is objtool for x86_64 only?

alison — Tue, 01 Aug 2017 05:36:38 +0000

There are a legion of readers who work exclusively on ARM processors. I'm disappointed to read the entire article and then realize, looking at the source tree, that "at least on the x86 architecture" meant that the ORC format is not supported on any processors I work with. It would be nice to see a clearer statement of architecture-specificity in the first paragraph.

User space

alkbyby — Sat, 22 Jul 2017 02:02:17 +0000

User space is likely to need more complex unwinding support. Since it has wider set of possible compilers/runtimes and programming language features. I.e. at least unwinding RBP is likely to be needed.

User space

corbet — Thu, 20 Jul 2017 21:06:38 +0000

That's a question that came up in the conversation; I didn't manage to work it into the article, sorry. There is definitely interest in doing that, and it seems possible, but nobody is working on it at the moment.

The ORCs are coming

Sesse — Thu, 20 Jul 2017 20:58:11 +0000

A related question; will this eventually seep down into userspace, so that we can get reliable perf backtraces without frame pointers? (Yes, there's --call-graph=dwarf, but it requires dumping the entire stack to the perf trace, since DWARF is too slow to trace in realtime. So it makes for slow, huge traces.)

The ORCs are coming

corbet — Thu, 20 Jul 2017 19:57:28 +0000

ORC will track neither of those things; it just provides the information needed to make sense of the kernel stack. The kallsyms mechanism can associate symbols with addresses, as always.

The ORCs are coming

jhoblitt — Thu, 20 Jul 2017 19:53:41 +0000

I haven't tried to grok the pathset... Will ORC track file/lineno or just symbol name?