Bug 58209 - LLVM/bitcode can't handle filter clauses
Summary: LLVM/bitcode can't handle filter clauses
Status: CONFIRMED
Alias: None
Product: iOS
Classification: Xamarin
Component: Mono runtime / AOT compiler (show other bugs)
Version: master
Hardware: PC Mac OS
: --- normal
Target Milestone: Future Cycle (TBD)
Assignee: Zoltan Varga
URL:
Depends on:
Blocks:
 
Reported: 2017-07-18 11:39 UTC by Rolf Bjarne Kvinge [MSFT]
Modified: 2017-10-05 16:16 UTC (History)
3 users (show)

Tags:
Is this bug a regression?: No
Last known good build:

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Status:
CONFIRMED

Description Rolf Bjarne Kvinge [MSFT] 2017-07-18 11:39:42 UTC
LLVM does not support filter clauses in exception handling, and we fall back to the JIT.

This is a problem on watchOS, where bitcode does not allow us to fall back to the JIT, and at runtime we end up with assertions/exceptions.
Comment 1 Rolf Bjarne Kvinge [MSFT] 2017-07-18 11:41:24 UTC
I have a POC of a new linker step that detects filter clauses when building for bitcode, and replaces the corresponding method with an exception, and reports a warning at build time: https://github.com/rolfbjarne/xamarin-macios/commit/f1d46b4b1c94fcea92718d1a4d1321f371ed2482 (this POC detects fault clauses as well, since it was implemented before support for fault clauses was implemented in the mono runtime).
Comment 2 Rolf Bjarne Kvinge [MSFT] 2017-07-18 11:44:37 UTC
This new linker step runs even if the linker is disabled (although that should be a very rare scenario for watchOS apps, since with the linker disabled the app ends up being too big for the App Store).
Comment 3 Rolf Bjarne Kvinge [MSFT] 2017-10-04 18:33:12 UTC
One major advantage of the linker step is that it makes debug and release builds behave the same (i.e. no surprises when running the release build)