[release/5.0-rc2] Properly handle byrefs in tailcall helper stubs #41875
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Switch to using ByReference instead of using stind.i/ldind.i and relying on the JIT to report the locations being moved between. Fixes #41555
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BruceForstall
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Sep 4, 2020
jeffschwMSFT
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Approved. Please get a cr and a clean ci. I will take it for RC2 consideration
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Backport of #41815 to release/5.0-rc2
/cc @BruceForstall @jakobbotsch
Customer Impact
This fixes a GC hole that could cause a crash or data corruption. This could happen in a small window for tail call functions via the new tailcall-via-helper mechanism if byref arguments were passed.
The original issue is #41555
Testing
Our full complement of CI GCStress runs was performed; the originally failing test was not observed to be failing any more. Additionally, @BruceForstall manually examined GC info for the tailcall helper stubs for the previously failing test, and observed the change looked correct.
Risk
low