[LLVMdev] ARM unwinding bug (original) (raw)

Mason Wheeler masonwheeler at yahoo.com
Wed Jul 29 14:23:06 PDT 2015

From: Renato Golin <renato.golin at linaro.org>

On 29 July 2015 at 20:14, Mason Wheeler <masonwheeler at yahoo.com> wrote: > Well, yes, an unwinding expert was who I was really hoping to hear from. But > if I understand correctly, you're saying that rather than seeing the values Ben > reported, the sample code crashes on you on both compilers? I do notice that > you're using different versions of both compilers than he was, which may or may > not be relevant. What hardware was this on? Ben said he's been using a > Raspberry Pi, not sure which model. Yes, so, that's yet another missing info. Which ARM? RaspberyPi, although popular, is a very old and somewhat deprecated architecture (ARMv6). Most people work on ARMv7 and ARMv8 nowadays, so if you can't reproduce the bugs on those, you'll have a hard time finding people to help you.

I asked Ben, and he says he's using the Raspberry Pi 2 (ARM 7) model.

Also, Clang 3.6 is not that old, but we don't really provide maintenance to non-trunk versions of the compiler, so if you want a bug looked into, you need to reproduce it in trunk. If you can't, than the problem is fixed, and you either wait for the new release to come out, or build your own from trunk.

OK, we'll try that.

> In the meantime, can you provide details of the crash you're observing? > Just saying "it crashes on FooBarBaz," which is not even mentioned anywhere in > the source of the test case, doesn't provide much useful information. At the > risk of trotting out one of the oldest cliches in the book, this works (or at > least breaks as described) on our end! :P

That's the catch. I know that unwstep() calls UnwindVRSPop() while loading the stack frame, because you need the context of that frame, so for me that looked like a good thing to say. If you report a bug in the unwinder, I expect you to either understand a bit about it (like me), or to have

someone at your disposal that do.

That would be Ben. :)

If out of those 20 million developers, not a single one can help you,> then maybe it's not that important for them...

Meh. It's more of a "if you build it, they will come" thing. We haven't finished building it yet, but when we do, they will come! :D

> Forgive my saying so, but that seems like a bizarre attitude, as you've > already admitted that you don't know much about unwinding. Isn't that the > entire point of specialization?

I have worked with unwinding some years ago, but the knowledge is very specific and I forgot most of it. That's why I still have a look around, but I'm no specialist, by far. Logan and Anton are the guys you're looking for.

Awesome. I hope one of them sees this then. :)

Would you rather I didn't look at it, or replied to your email, if I'm not the specialist? (this is a genuine question)

Genuine answer: If you do know something, I'd rather you reply with that and contribute what you can, even if you don't know everything. Every little contribution can be helpful.

There is no such thing as free lunch. But if you want to share your lunch with me, and if I would like to have half of your sandwich, I'd be glad to give half of mine to you.

Makes sense?

Makes perfect sense to me. Share with me a fix for this bug, and in return I'll happily share with you my ARM32 CLR, and the Android support, once we get them working. :D

Mason

More information about the llvm-dev mailing list