Support for `io_uring`

[sugarraysam]

Hello, as titled I am running into unsupported syscall error in my project, where I do use io_uring.

// from kernel - 425 maps to `io_uring_setup`
uapi/asm-generic/unistd.h
759:#define __NR_io_uring_setup 425
760:__SYSCALL(__NR_io_uring_setup, sys_io_uring_setup)

// Error log from miri
$ cargo +nightly test miri` test runtime::cancel::tests::test_cancel_timeout_multishot ... error: unsupported operation: syscall: unsupported syscall number 425
   --> /home/doodly/opt/io-uring/src/sys/mod.rs:115:15
    |
115 |     to_result(syscall(SYSCALL_SETUP, entries as c_long, p as c_long) as _)
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unsupported operation occurred here

I tried digging into the codebase, and am finding the syscall() function in src/shims/unix/linux_like/syscall.rs, but could not decipher exactly the path ahead to adding support for this syscall.

Thank you for the help.

[RalfJung]

Yeah, we have no support for io_uring at the moment... and I assume that's pretty far out.

[sugarraysam]

Is there another path forward where we first "ignore" io_uring related syscalls so the rest of miri can still work on the project?

I don't care for full io_uring support, I just wanted to use regular miri in the codebase.

[bjorn3]

You can use #[cfg(miri)] to run different code in miri than on regular builds. Miri can't just ignore unknown syscalls however. Syscalls can make arbitrary modifications to the program state, ignoring which can easily cause the program to have UB. ANd besides miri wouldn't know what return value to return for the syscall.