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Fix use of uninitialized variables in managed decimal implementation #25674
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The CoreFX tests have not hit this problem because of the stacklayout from XUnit is very predictable with the specific stack locations all typically being zero by luck. |
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@MeiChin-Tsai Could you please approve this change? |
stephentoub
approved these changes
Jul 13, 2019
| @@ -156,6 +156,13 @@ private ulong Low64 | |||
| 1e80 | |||
| }; | |||
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| // Used to fill uninitialized stack variables with non-zero pattern in debug builds | |||
| [System.Diagnostics.Conditional("DEBUG")] | |||
| private static unsafe void Poison<T>(ref T s) where T: unmanaged | |||
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Nit: maybe DebugPoison so the debug-only-ness is clearer at call site?
Would it make sense for the future to add a mode for the JIT where non-initlocals are poisoned in a similar way? |
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Yes, that would make sense - especially if the skipinitlocals becomes more mainstream. Filled https://github.com/dotnet/coreclr/issues/25683 |
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I have noticed that decimal multiplications and divisions return bogus results intermittently while working on unrelated issues. It turns out a few places in the new managed decimal implementation use uninitialized stack variables. I have added debug-only instrumentation to catch these.