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

[Adrian Vogelsgesang via lldb-commits]

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!
>
>
>
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