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POSIX readv()/preadv()/writev()/pwritev() do not use all buffers under preview 2 (as found by Python)Â #7830
Closed as not planned
Description
Test Case
TODO: upload Wasm file here
Steps to Reproduce
- https://github.com/python/cpython/blob/07236f5b39a2e534cf190cd4f7c73300d209520b/Lib/test/test_posix.py#L520-L525
- https://github.com/python/cpython/blob/07236f5b39a2e534cf190cd4f7c73300d209520b/Lib/test/test_posix.py#L307-L311
- https://github.com/python/cpython/blob/07236f5b39a2e534cf190cd4f7c73300d209520b/Lib/test/test_posix.py#L487-L490
- https://github.com/python/cpython/blob/07236f5b39a2e534cf190cd4f7c73300d209520b/Lib/test/test_posix.py#L364-L369
Expected Results
To be told 10 bytes were read/written.
Actual Results
5 bytes, which matches the first buffer, not the total bytes written across all buffers.
Versions and Environment
Wasmtime version or commit: 17.0.0
Operating system: Linux/WSL
Architecture: x64
Extra Info
Success logs when testing readv():
success-readv.txt
Failuse logs:
failure-readv.txt
Activity
[-]POSIX `readv()`/`preadv()`/`writev()`/`pwritev()` misreporting number of bytes read under preview 2 (as found by Python)[/-][+]POSIX `readv()`/`preadv()`/`writev()`/`pwritev()` misreporting number of bytes read/written under preview 2 (as found by Python)[/+]brettcannon commentedon Jan 26, 2024
If I'm looking this up right,
wasmtime/crates/wasi/src/preview2/preview1.rs
Line 1309 in 5c0027b
wasmtime/crates/wasi-preview1-component-adapter/src/lib.rs
Line 989 in 5c0027b
bjorn3 commentedon Jan 26, 2024
The preview2 based preview1 implementation which is now used by default indeed only looks at the first buffer. See also #7757. wasi-preview1-component-adapter also only looks at the first buffer as far as I can see.
alexcrichton commentedon Jan 26, 2024
Yes I can confirm that this is expected right now. It's expected that this is still posix-conformant in that posix doesn't guarantee everything is written. Vectored reads/writes aren't present in preview2 so they're polyfilled from preview1 by looking at the first buffer.
brettcannon commentedon Jan 26, 2024
As in this isn't expected to change? I think I can mark those POSIX functions as unsupported in https://github.com/python/cpython/blob/main/Tools/wasm/config.site-wasm32-wasi so the tests pass if you plan to keep the current semantics.
alexcrichton commentedon Jan 28, 2024
Correct yeah, that's not expected to change.
[-]POSIX `readv()`/`preadv()`/`writev()`/`pwritev()` misreporting number of bytes read/written under preview 2 (as found by Python)[/-][+]POSIX `readv()`/`preadv()`/`writev()`/`pwritev()` do not use all buffers under preview 2 (as found by Python)[/+]brettcannon commentedon Jan 29, 2024
I've tweaked the title and closing this as it's working as intended. I'll patch CPython to consider these functions as unavailable.
pythonGH-115978: Disable `*readv()` and `*writev()` on WASI
GH-115978: Disable `*readv()` and `*writev()` on WASI (GH-116228)
pythonGH-115978: Disable `*readv()` and `*writev()` on WASI (pythonGHâĶ
pythonGH-115978: Disable `*readv()` and `*writev()` on WASI (pythonGHâĶ
[3.12] GH-115978: Disable `*readv()` and `*writev()` on WASI (GH-116228âĶ
2 remaining items
pythonGH-115978: Disable `*readv()` and `*writev()` on WASI (pythonGHâĶ
pythonGH-115978: Disable `*readv()` and `*writev()` on WASI (pythonGHâĶ
python311 py311-html-docs: updated to 3.11.9
python312 py312-html-docs: updated to 3.12.3
python312 py312-html-docs: updated to 3.12.3
pythonGH-115978: Disable `*readv()` and `*writev()` on WASI (pythonGHâĶ
python311 py311-html-docs: updated to 3.11.9
python312 py312-html-docs: updated to 3.12.3
python312 py312-html-docs: updated to 3.12.3
python311 py311-html-docs: updated to 3.11.9
python312 py312-html-docs: updated to 3.12.3
python312 py312-html-docs: updated to 3.12.3
python311 py311-html-docs: updated to 3.11.9
python312 py312-html-docs: updated to 3.12.3
python312 py312-html-docs: updated to 3.12.3