Use uninitialized buffers for read and recvfrom
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Currently, when using an uninitialized buffer for `read`, as would be typical in C or required for `Read::read_buf`, it is casted from `*mut u8` at the FFI boundary in `sys_read`/`sys_readv` to a `&[u8]`. I think this is unsound. Instead, use `&[MaybeUninit<u8>]` internally. I use this instead of `core::io::BorrowedCursor<'_>`, because there are currently no cases where the initialized portion needs to be separately tracked. This enables implementing `std::io::Read::read_buf` for `std::fs::File` and `std::io::Stdin` on Hermit. That effort is tracked in rust-lang/rust#136756.
Since `smoltcp::socket::tcp::Socket::recv_slice` takes a `&[u8]`, inline it and refactor. As a bonus, this avoids a copy and clear in the error case and it makes it more clear that packets are dropped when given an insufficiently large buffer.
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The CI failure seems likely to be unrelated: |
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How should I coordinate with the Hermit side when I submit the PR to Rust for |
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The kernel is built separately from the application and then linked together without LTO at the moment, so I think the chances of something bad happening due to undefined behavior are really slim in this case. So I'd say you can go ahead with that PR right away. Feel free to Tag @stlankes and me in everything Hermit-related to keep us in the loop, of course. :) |
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Currently, when using an uninitialized buffer for
readorrecvfrom, as would be typical in C or required forRead::read_buf, it is casted from*mut u8at the FFI boundary insys_read/sys_readv/sys_recvfromto a&[u8]. I think this is unsound. Instead, use&[MaybeUninit<u8>]internally.I use
&[u8]instead ofcore::io::BorrowedCursor<'_>, because there are currently no cases where the initialized portion needs to be separately tracked.Since
smoltcp::socket::tcp::Socket::recv_slicetakes a&[u8], inline it and refactor. As a bonus, this avoids a copy and clear in the error case and it makes it more clear that packets are dropped when given an insufficiently large buffer.This PR enables implementing
std::io::Read::read_bufforstd::fs::Fileandstd::io::Stdinon Hermit. That effort is tracked in rust-lang/rust#136756.