Testing with deep checking reports false positives

[rptb1]

#205 says:

... a build with make -f lii6ll.gmk VARIETY=cool CFLAGSDEBUG='-O0 -g3 -DCHECKLEVEL=CheckLevelDEEP' testci currently fails in several tests.

and also:

We should build and run a deep checking build on at least one platform.

Several steps are needed:

1. Introduce an easier way to build and test with deep checking.
2. Add testing with deep checking to CI so that we catch problems early.
3. Analyse and fix current test failures with deep checking.

I have found false positives in deep checking errors have been introduced in various changes:

1. branch/2016-04-16/trace-gens finishes the ring of generations but goes on to use the arena with an invalid trace.
2. branch/2020-08-31/walk synthesizes a trace that fails to pass TraceCheck because it has no generations.
3. Deep checking has an infinite recursion in ArenaCheck via ShieldCheck, which checks some segments, which check their addresses via ChunkOfAddr, which checks the arena with ArenaCheck. I haven't discovered when this was introduced yet.
4. ArenaRootsWalk synthesizes an invalid trace in TraceStateINIT that is flipped. ArenaRootsWalk dates back to 1999 so it was introduced by some other change. I haven't discovered when yet.

There may be more. I have yet to run the entire test suite.

So far I have no evidence that any of these would cause failures in production, but deep checking is a valuable tool when, e.g. working on subtle parts of the MPS like the shield, and we ought to fix it up.

[rptb1]

We should check whether CHECKLEVEL_DYNAMIC (using a variable to control checking levels) has a reasonable overhead and perhaps use it by default for the cool variety. That would avoid proliferation of varieties and allow for easy switching to deep checking without rebuilding.

[rptb1]

We should probably include a deep checking run in our release procedure along with the other testing methods. See also #125

[rptb1]

I was investigating the process issues around this, and thought I'd note here the related issues I found.

• job003302 mps_arena_create fails with deep consistency checks
• job003692 MPS deep checking fails at bootstrap
• job004026 Failed shield assertions with DEEP checking