Fix off-by-one error in TypePreinit switch instruction handling #123911
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…et#123833) The switch IL instruction interpreter used > instead of >= when checking if the switch value exceeds the case count. Per ECMA-335, switch should fall through to the next instruction when value >= count, but the code only did this for value > count. When value exactly equals count, the code tried to read a non-existent jump table entry, corrupting the IL reader offset and causing an IndexOutOfRangeException during NativeAOT compilation. Added test case for the boundary condition (value == case count).
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Tagging subscribers to this area: @agocke, @dotnet/ilc-contrib |
MichalStrehovsky
approved these changes
Feb 2, 2026
This was referenced Feb 3, 2026
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Summary
Fixes #123833
The switch IL instruction interpreter in TypePreinit used
>instead of>=when checking if the switch value exceeds the case count. Per ECMA-335, switch should fall through to the next instruction whenvalue >= count, but the code only did this forvalue > count.When the value exactly equals the case count, the code tried to read a non-existent jump table entry, corrupting the IL reader offset and causing an
IndexOutOfRangeExceptionduring NativeAOT compilation.Changes
target > counttotarget >= countin the switch instruction handler