D272 - Out-parameters are written at their declared width

Status: decided Date: 2026-08-25

An implementation writes an out-parameter at the width of the type it points to: four bytes through an int *, a full word through a pointer-sized slot. A pointer-to-pointer argument is a handle the implementation allocates and writes back, not the object itself.

Why: writing a word through an int * overwrites the caller's neighbouring variable, and that corruption surfaces far from the call. Treating &attr as the attribute object overwrites the guest's own pointer variable.

Rejected:

• Writing a full word everywhere: corrupts the neighbouring stack slot.
• Treating a double pointer as the object: overwrites the guest's variable with a value.