Bug 38765 - Support for accurate process/thread state in crash reports
Summary: Support for accurate process/thread state in crash reports
Status: CONFIRMED
Alias: None
Product: iOS
Classification: Xamarin
Component: XI runtime (show other bugs)
Version: unspecified
Hardware: PC Mac OS
: --- enhancement
Target Milestone: Future Cycle (TBD)
Assignee: Bugzilla
URL:
Depends on:
Blocks:
 
Reported: 2016-02-15 14:34 UTC by Rolf Bjarne Kvinge [MSFT]
Modified: 2017-01-19 06:36 UTC (History)
1 user (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
CONFIRMED

Description Rolf Bjarne Kvinge [MSFT] 2016-02-15 14:34:35 UTC
This is a spin-off bug from bug #4120.

Currently for SIGSEGVs, Mono will:

1) Handle the SIGSEGV
2) Check if it's in managed code (if it is, throw a NullReferenceException. That's not what this bug is about).
3) If in native code, print diagnostics to stderr/logs.
4) Raise SIGABRT.

The problem here is 4), when raising SIGABRT the register/thread/process state from the SIGSEGV is lost, and it may contain information crucial to diagnose a crash (see bug #4120, comments 22/24 for examples).

Suggestion:

1) Add support to enable crash chaining [1]. This must be opt-in, because currently crash reporters depend on us raising SIGABRT for SIGSEGVs we recognize as NullReferenceExceptions [2].

  a) Using an argument to mtouch: --enable-crash-chaining. Pro: easy to implement. Con: hard to set from third-party libraries (which is usually how crash reporters are consumed by customers).
  b) Using an assembly-level attribute. [assembly: CrashChaining (true)]. Con: harder to implement (but not very hard I think). Pro: can easily be configured from third-party libraries.

2) Add support for providing a native method that initializes crash reporters (so that the signal handlers for the crash reporter is installed before Mono's).

  a) Using an argument to mtouch. --crash-reporter-initialization-function:<function name>
  b) Using an assembly-level attribute.

  Same cons/pros as for 1).

3) Add support for 1) and 2) to Xamarin.Insights.

[1] https://github.com/mono/mono/commit/8ffc4070a94c5c3ef73b99e836e1b1e5652dffba
[2] http://stackoverflow.com/a/14499336/458193
Comment 1 Rolf Bjarne Kvinge [MSFT] 2017-01-19 06:36:33 UTC
2) Is already implemented: https://github.com/mono/mono/commit/aaaead4. This will be in C9.

There's also another option for 1):

c) Automatically detect apps that call https://github.com/mono/mono/commit/aaaead4, and then enable crash chaining.