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Coerce call arguments according to ECMA-335

  • Article

ECMA-335 (Table III.9: Signature Matching) describes which implicit conversions are supported for call arguments. This change adds checking for the supported conversions.

Version introduced

6.0

Change description

In previous .NET versions, the just-in-time (JIT) compiler does not coerce call arguments according to ECMA-335. This leads to undefined behavior on some platforms. For example, on x86, passing a long value as an int register leaves the register undefined.

Starting in .NET 6, if implicit conversion is not allowed, then the JIT compiler throws an InvalidProgramException. There are two conversion cases that are still allowed:

  • int8 -> nint on 64-bit platform (because it's used often and doesn't lead to bad code)
  • byref -> nint

Reason for change

The previous behavior caused silent, bad code generation on some platforms, including Arm64 Apple.

If you updated to .NET 6 and your app throws InvalidProgramException exceptions because of this change, use an explicit conversion for the affected argument or fix the callee declaration.

Affected APIs

None.