non-deterministically truncate reads/writes #4481
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RalfJung
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RalfJung
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Jul 19, 2025
src/shims/windows/fs.rs
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| @@ -462,6 +463,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> { | |||
| }; | |||
| let io_status_info = this.project_field_named(&io_status_block, "Information")?; | |||
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| // It seems like short writes are not a thing on Windows, so we don't truncate `count` here. | |||
| // FIXME: if we are on a Unix host, short host writes host are visible to the program! | |||
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@CraftSpider is it correct that partial reads/writes are not a thing on Windows?
https://stackoverflow.com/questions/62438021/can-ntreadfile-produce-a-short-read-without-reaching-eof seems fairly clear here.
OTOH that also says that io_status_info would not be written on failure, whereas we always reset it to 0...
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Fixes #4369: with 50% chance, we only read/write half the requested buffer. This quickly found some issues in our test suite.^^