Bug 6112 - AOT: Crash in imt_thunks
Summary: AOT: Crash in imt_thunks
Status: RESOLVED FIXED
Alias: None
Product: Runtime
Classification: Mono
Component: General ()
Version: unspecified
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Bugzilla
URL:
Depends on:
Blocks:
 
Reported: 2012-07-13 09:58 UTC by Virgile Bello
Modified: 2012-07-16 12:15 UTC (History)
3 users (show)

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


Attachments
File reproducing the issue. (780 bytes, text/plain)
2012-07-13 09:58 UTC, Virgile Bello
Details


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Status:
RESOLVED FIXED

Description Virgile Bello 2012-07-13 09:58:56 UTC
Created attachment 2192 [details]
File reproducing the issue.

Attached file reproduces the issue (happens only in full AOT).
Crashes happen in "imt_thunks" (output: Trace/breakpoint trap (core dumped))

I investigated little bit in mono internals and found it was due to imt_thunks. Checked imt_thunks assembly code (seems good) and generated/called IMT thunks.

Basically, it seems the issue is that, in this test case, IEnumerable<A>.get_Current() is the method registered registered in IMT, but IEnumerable<object>.get_Current() is the one requested (probably due to contravariance).

Note that interestingly, it fails only when requesting the second item (second call to IEnumerable<object>.get_Current(), first one seems OK). Actually in this case the bug only happens when collection has more than 1 element.

It also happened in some other cases as well that seemed related to collections/enumerables, easily triggered when using Linq and/or using collections (not sure yet how much will be working by fixing this specific test).

I plan to try to fix it next week when I get back to work, but if someone happens to know better the internals and how to fix it quickly, some hints/confirmation/help would be welcome!
Comment 1 Zoltan Varga 2012-07-15 09:00:02 UTC
Fixed in master.
Comment 2 Virgile Bello 2012-07-15 22:32:28 UTC
Thank for your help, saw the fix.
However I couldn't test it because I run in x64 full aot, do you think it's possible to fix it for x64 as well?
Comment 3 Zoltan Varga 2012-07-15 23:14:09 UTC
Should be fixed.
Comment 4 Virgile Bello 2012-07-16 11:34:08 UTC
Thanks for your help, looks good!

I could test it and there was a small compilation error (mono_x86_patch renamed to mono_amd64_patch) and also I removed extra indirection (amd64_mov_reg_membase => amd64_alu_reg_imm: causing crash).

I fixed it in pull request: https://github.com/mono/mono/pull/391
Please merge it if it looks good to you!
Comment 5 Zoltan Varga 2012-07-16 12:15:22 UTC
-> fixed.