Rust miri test error caused by `mlock`, `munlock` and `madvise` of libc

When running cargo +nightly miri test, encounter the error:

error: unsupported operation: can't call foreign function `mlock` on OS `linux`

This occurs because Miri (Rust’s MIR interpreter) does not fully emulate all system calls or OS-specific functions like mlock (which locks memory pages to prevent swapping). Miri’s sandboxed environment restricts direct interaction with the OS, causing this error.

Solutions

1. Bypass libc functions in Tests (Conditional Compilation)

Use Rust’s cfg attributes to skip mlock during Miri tests:

// In your code where `mlock` is called:  
#[cfg(not(miri))]  // Skip this block when running Miri  
{  
    unsafe {  
        libc::mlock(ptr, len);  
    }  
}

2. Mock libc functions for Miri

Replacing libc functions with a no-op allows tests to proceed without triggering errors. For dependencies that require mlock, create a mock implementation when testing with Miri:

#[cfg(miri)]
mod mock {
    // Replace `mlock` with a no-op during Miri tests
    #[no_mangle]
    pub unsafe extern "C" fn mlock(_addr: *const libc::c_void, _len: libc::size_t) -> libc::c_int {
        0 // Return success
    }

    #[no_mangle]
    pub unsafe extern "C" fn munlock(addr: *const libc::c_void, len: libc::size_t) -> libc::c_int {
        0
    }

    #[no_mangle]
    pub unsafe extern "C" fn madvise(
        addr: *const libc::c_void,
        len: libc::size_t,
        advice: libc::c_int,
    ) -> libc::c_int {
        0
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_with_libc() {
       // code 
    }
}

Key Components: Override mlock, munlock, and madvise with #[no_mangle]

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