Address COM interop case involving legacy wCode usage.
#117596
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The wCode field in the EXCEPINFO is a 16-bit signed integer. This is a legacy field for 16-bit Windows, but is still used in many COM servers. The current implementation assumed it would result in an Exception using Marshal.GetExceptionForHR(), but converting a short to an int, will rarely result in a negative value which means null will almost always be returned. This change checks if the exception is null and if so, creates a simple COMException with the error code.
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Pull Request Overview
This PR fixes a bug in COM interop exception handling where legacy 16-bit wCode values were not properly converted to exceptions. The issue occurred because converting a short to an int rarely produces negative values, causing Marshal.GetExceptionForHR() to return null instead of a proper exception.
- Adds null-checking logic to create a fallback
COMExceptionwhenMarshal.GetExceptionForHR()returns null - Updates method signatures and null checks to use modern C# nullable reference types and patterns
- Improves code documentation with detailed comments explaining the legacy
wCodebehavior
src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ExcepInfo.cs
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src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ExcepInfo.cs
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Tagging subscribers to this area: @cston |
jkoritzinsky
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Jul 14, 2025
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/bg-a Android timeout |
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/ba-g Android timeout |
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/backport release/9.0-staging |
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/backport to release/9.0-staging |
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Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/16283173445 |
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The
wCodefield in theEXCEPINFOis a 16-bit signed integer. This is a legacy field for 16-bit Windows, but is still used in many COM servers. The current implementation assumed it would result in anExceptionusingMarshal.GetExceptionForHR(), but converting ashortto anint, will rarely result in a negative value which meansnullwill almost always be returned. This change checks if the exception isnulland if so, creates a simpleCOMExceptionwith the error code.Fixes #117568