[Lldb-commits] green dragon testsuite crash on TestCoroutineHandle.py from coroutines formatter changes, temporarily revert?

Fri Nov 25 18:20:52 PST 2022

Hi Adrian, thanks for digging in.  I am not sure about the policies of the builders, I think we had failing test cases for a bunch of days & it may have already been red when your change went in, so it wasn't detected as a change in status.  That might have something to do with it.  I thought the behavior was like you described, too.

I don't know what tools are installed on the builder but I'll ask around the office on Monday, I know there are people who are more familiar with how these bots are set up.

J

> On Nov 25, 2022, at 2:22 PM, Adrian Vogelsgesang <avogelsgesang at salesforce.com> wrote:
> 
> Hm... wait a second...
> 
> Which clang-version is https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/ using? Is it using an older version of clang? Does that version already contain the patch https://reviews.llvm.org/D132580?
> 
> If not, that might explain things...
> 
> On Fri, Nov 25, 2022 at 11:18 PM Adrian Vogelsgesang <avogelsgesang at salesforce.com> wrote:
> Hi Jason,
> 
> Sorry for the late reply - your mail got caught in my spam filter, and I just realized about the build breakage now after you reverted the commits. Just to confirm: 
> 
> I looked at the original change again, and I think I know what's going wrong here: Devirtualization fails, and `promise_type` stays `void`. Obviously, `CreateValueObjectFromAddress` cannot create an object of type `void` and fails. The previous version was robust against that scenario, but https://reviews.llvm.org/D132815 accidentally regressed this.
> 
> If a program has all the expected debug info, devirtualization should never fail and `promise_type` never stays `void`. It seems something is wrong/unexpected with the debug info on Darwin. Devirtualization relies on being able to identify the function pointer of the `destroy` function and inspects that function. So the root cause seems to be the same as for the revert https://github.com/llvm/llvm-project/commit/2b2f2f66141d52dc0d3082ddd12805d36872a189: For some reason, the debugger cannot find debug info for the function pointed to by the `destroy` function.
> 
> However, I still don't quite understand what's wrong with the debug info on Mac.
> 
> Either way, the pretty printer should of course be robust against such unexpected debug info. I think a simple additional check should be enough to make this robust so we no longer crash:
> if (!promise_type.isVoid()) { // <---- additional check
>   lldb::ValueObjectSP promise = CreateValueObjectFromAddress(
>       "promise", frame_ptr_addr + 2 * ptr_size, exe_ctx, promise_type);
>   Status error;
>   lldb::ValueObjectSP promisePtr = promise->AddressOf(error);
>   if (error.Success())
>     m_promise_ptr_sp = promisePtr->Clone(ConstString("promise"));
> }
> 
> Meta question: I am a bit confused about https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/. I thought LLVM's buildbots were set up to send an email in case somebody breaks the build. Also, I made sure that all builds in https://lab.llvm.org/buildbot/#/builders stayed green after my commit. So what are the expectations around which CIs need to stay green after a commit? Do I need to setup anything such that green.lab.llvm.org also sends me an email if I break it?
> 
> Cheers,
> Adrian
> 
> On Thu, Nov 24, 2022 at 10:50 PM Jason Molenda <jason at molenda.com> wrote:
> Ah, little misstatement below.  My first thought was that promise_type was null, but when I stepped through here with a debugger, it was not.  I didn't know how to dig in to a CompilerType object but there was some reason why this CreateValueObjectFromAddress failed to return an actual ValueObject, and I assumed it's something to do with that CompilerType.  But I didn't dig in far enough to understand what the issue in the type was.
> 
> > On Nov 24, 2022, at 1:20 PM, Jason Molenda <jason at molenda.com> wrote:
> > 
> > Hi Adrian, the green dragon Incremental CI bot has been failing the past couple of days after the changes for the coroutines formatter, most directly   https://reviews.llvm.org/D132815 landed - TestCoroutineHandle.py results in a segfault on Darwin systems (both on the CI and on my mac desktop) consistently.   https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/
> > 
> > It's crashing in formatters::StdlibCoroutineHandleSyntheticFrontEnd where you're doing
> > 
> > ```
> >  // Add the `promise` member. We intentionally add `promise` as a pointer type
> >  // instead of a value type, and don't automatically dereference this pointer.
> >  // We do so to avoid potential very deep recursion in case there is a cycle in
> >  // formed between `std::coroutine_handle`s and their promises.
> >  lldb::ValueObjectSP promise = CreateValueObjectFromAddress(
> >      "promise", frame_ptr_addr + 2 * ptr_size, exe_ctx, promise_type);
> >  Status error;
> >  lldb::ValueObjectSP promisePtr = promise->AddressOf(error);
> > ```
> > 
> > and the promise_type dose not have a CompilerType so promisePtr is nullptr and we crash on the method call to AddressOf. I looked briefly, but this isn't a part of lldb I know well and I'm not sure the nature of the problem.
> > 
> > It's a long weekend in the US, so if you have a suggestion for addressing this that'd be great, or I can roll back the changes necessary to get the bot clean later today and we can look at this next week.  
> > 
> > Thanks!
> 
> 