dotnet/runtime

Null checks in incorrect order in Cordb::Terminate

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#47,463 opened on Jan 26, 2021

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area-Diagnostics-coreclrhelp wanted

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Description

There's a null-check for m_rcEventThread in Cordb::Terminate here:

https://github.com/dotnet/runtime/blob/3f12b16fa6db2b2ca5c9016ed9540547a3e752d5/src/coreclr/debug/di/rsmain.cpp#L1125

But the variable is already used without null-testing a littler earlier in the same method:

https://github.com/dotnet/runtime/blob/3f12b16fa6db2b2ca5c9016ed9540547a3e752d5/src/coreclr/debug/di/rsmain.cpp#L1079

If the variable was actually null, dereferencing it leads to undefined behaviour, so a compiler is free to assume that wont happen. A recent compiler might therefore remove the null check on line 1125 entirely. We should probably null-check m_rcEventThread everywhere, or remove the null-checks.

Contributor guide

Research direction
Examine the code in rsmain.cpp around lines 1079 and 1125. Understand the usage of m rcEventThread and determine if it can be null. Then either add null checks where needed or remove the unnecessary null check to ensure consistent handling.
Tech stack
cpp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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1-3 hours
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Active
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Clear
Prerequisites
C++
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75