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interp: keep partial loads independent of buffers owned by a caller's memory view - #5905
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… memory view A value that a function loads during package initialization must not change when the caller later stores to the same object. Since f5bd750, a partial store changes the buffer of an object in place when the current memory view already owns that object. 3a0d724 made load copy the loaded slice in that case, but it checked only the current view. When a callee loads part of an object that its caller owns, the callee has its own view, so the returned value still shares the caller's buffer, and the caller's next partial store changes it. For example, an init function that sets a struct field to 1, reads it through a helper function, sets it to 2, and then copies the value it read gives 2 instead of 1. This needs no defer and no revert, and the 0.43.0 release has the same problem. Objects in the runner's base table are never changed in place, so loads from objects that no view owns still return a slice of the buffer without a copy. The problem was found during review of tinygo-org#5903. This change does not depend on tinygo-org#5903 or on the getWritable fix on dfc/interp-getwritable-rollback.
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Oct 17, 2026
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Looking good @davecheney thank you!
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A value that a function loads during package initialization must not change when the caller later stores to the same object. Since f5bd750, a partial store changes the buffer of an object in place when the current memory view already owns that object. 3a0d724 made load copy the loaded slice in that case, but it checked only the current view. When a callee loads part of an object that its caller owns, the callee has its own view, so the returned value still shares the caller's buffer, and the caller's next partial store changes it. For example, an init function that sets a struct field to 1, reads it through a helper function, sets it to 2, and then copies the value it read gives 2 instead of 1. This needs no defer and no revert, and the 0.43.0 release has the same problem.
Objects in the runner's base table are never changed in place, so loads from objects that no view owns still return a slice of the buffer without a copy.
The problem was found during review of #5903. This change does not depend on #5903 or on the getWritable fix on dfc/interp-getwritable-rollback.