Fix select missing stack map declarations for GC refs#12862
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fitzgen wants to merge 1 commit intobytecodealliance:mainfrom
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Fix select missing stack map declarations for GC refs#12862fitzgen wants to merge 1 commit intobytecodealliance:mainfrom
select missing stack map declarations for GC refs#12862fitzgen wants to merge 1 commit intobytecodealliance:mainfrom
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The `select` and typed `select` Wasm operators create new SSA values in Cranelift but were not calling `declare_value_needs_stack_map` on the result when the operand type is a GC reference. This meant the result, when kept on the Wasm operand stack (not stored in a local variable), would not appear in stack maps at subsequent safepoints. If a GC collection occurred at such a safepoint, the collector would not see the `select`'s result as a live GC root and could free the referenced object, leading to use-after-free. The fix checks `select`'s operand types for reference types and declares the result as requiring inclusion in stack maps when needed.
cfallin
approved these changes
Mar 28, 2026
| needs_stack_map | ||
| } | ||
| _ => false, | ||
| }) { |
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Could we wrap this predicate up in another environ helper? Something like environ.ty_needs_stack_map(ty)? The embedded match in a closure in an if is a little awkward otherwise
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The
selectand typedselectWasm operators create new SSA values in Cranelift but were not callingdeclare_value_needs_stack_mapon the result when the operand type is a GC reference. This meant the result, when kept on the Wasm operand stack (not stored in a local variable), would not appear in stack maps at subsequent safepoints.If a GC collection occurred at such a safepoint, the collector would not see the
select's result as a live GC root and could free the referenced object, leading to use-after-free.The fix checks
select's operand types for reference types and declares the result as requiring inclusion in stack maps when needed.