[llvm-dev] LLVM 10 ORC2 issue with symbol resolution

[Lang Hames via llvm-dev]

Hi Dibyendu,

I am a bit confused about this. I assumed that cantFail() will abort
> the process on error - but my process doesn't abort.
> I have cantFail() in a few places, I am not sure if you are suggesting
> adding the error logging everywhere ...


Are you building LLVM in +Asserts mode? I believe that cantFail should
abort in +Asserts builds, but it's effectively a no-op if asserts are
disabled.

If you are building in +Asserts mode it could also be consumeError: that
function is intended to silently consume errors.

Both cantFail and consumeError should be used very carefully. The cantFail
function should only be used if you are 100% certain that an error can
never occur at runtime if program invariants hold. E.g. adding a symbol to
a newly created JITDylib can't fail because there are no existing
definitions to clash with. The consumeError function should only be used if
you have genuinely dealt with whatever error condition arose. If you think
that an error is being silently dropped please see if you can trace it by
putting a breakpoint on the ErrorInfoBase constructor and destructor, then
following any errors generated up the stack to the point where they're
dropped. Silently dropped errors (in +Asserts mode) are likely bugs in the
llvm::Error system and we definitely want to get them fixed.

Regards,
Lang.

On Mon, Apr 13, 2020 at 1:46 PM Dibyendu Majumdar <mobile at majumdar.org.uk>
wrote:

> Hi Lang,
>
> On Mon, 13 Apr 2020 at 21:26, Lang Hames <lhames at gmail.com> wrote:
> >
> >> I had a look - to be honest I am not sure where the error is being
> >> reported from. It looks like this:
> >> JIT session error: Symbols not found: [ luaV_tointeger_, luaG_runerror ]
> >> I don't think it is from any logging I am doing.
> >
> >
> > Errors in ORC may trigger cascading failures. E.g. if two different
> modules M1 and M2 both reference a function "foo" which cannot be resolved,
> then you have three errors: A failure to resolve "foo", A failure to
> materialize the symbols in M1, and a failure to materialize the symbols in
> M2. When such a cascade occurs ORC will usually report the original
> error(s) via ExecutionSession::reportError (which logs them to stderr by
> default) and return a derived error (e.g. failure-to-materialize) to
> callers. I believe you're seeing the logged error, and you will see a
> failure-to-materialize error if you log the result that reaches cantFail in
> your example above.
> >
>
> I am a bit confused about this. I assumed that cantFail() will abort
> the process on error - but my process doesn't abort.
> I have cantFail() in a few places, I am not sure if you are suggesting
> adding the error logging everywhere ...
>
> Thanks and Regards
> Dibyendu
>
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