Linux 3.10.0-693.2.2.el7.x86_64 seems to somehow expose inconsistent sysctl API

[przygienda]

ewnough said, API changed in mutability on first parameter and ptr/size? and that breaks crates like e.g. sysctl ...

[gnzlbg]

ewnough said,

libc has a million APIs, so it would at least be nice to know which API, which target triple, minimum working example (no dependencies) with instructions to reproduce, etc.

[przygienda]

nightly-x86_64-unknown-linux-gnu

sysctl(...) call changed mutability of parameters ...

reproduce: try to compile sysctl crate which takes libc and uses sysctl(..) calls

[gnzlbg]

Please read https://github.com/rust-lang/libc/pull/1312/files .

[gnzlbg]

The last commit that changed sysctl on x86_64-unknown-linux-gnu is from 2 years ago (343b7c1) and landed on libc 0.2.33. There aren't any commits between 0.2.50 and 0.2.51 touching that API.

[gnzlbg]

rust-semverver also reports no breaking changes between 0.2.50 and 0.2.51 on x86_64-unknown-linux-gnu (https://travis-ci.com/rust-lang/libc/jobs/188592924#L808, https://travis-ci.com/rust-lang/libc/jobs/188694789#L819) and it checks for changes in function signature types.

[przygienda]

thanks, yet somehow it looks like updating to .51 broke sysctl here. I will try to get you an example today to verify it's not something else

[przygienda]

Looked @ it further, it looks like an issues taht has nothing to do with newest libc release but been there since a bit. confusing, it compiles on other plaforms (BSD & MacOS)

Affects stable and nightly ...

--- here's the info, code taken out directly from sysctl-rs crate

extern crate libc;
use libc::{sysctl, c_int, c_void};

fn main() {
let oid: [c_int; 2] = [0, 3];

let mut len: usize = 32;

// We get results in this vector
let mut res: Vec<c_int> = vec![0; 32 as usize];

let name = "abc";

let ret = unsafe {
    sysctl(
        oid.as_ptr(),
        2,
        res.as_mut_ptr() as *mut c_void,
        &mut len,
        name.as_ptr() as *const c_void,
        name.len(),
    )
};

}
[prz@rahi-01 ~/gitlab/sysctl-break]$cargo +stable build
Compiling sysctl-break v0.1.0 (/home/prz/gitlab/sysctl-break)
error[E0308]: mismatched types
--> src/main.rs:16:13
|
16 | oid.as_ptr(),
| ^^^^^^^^^^^^ types differ in mutability
|
= note: expected type *mut i32
found type *const i32

error[E0308]: mismatched types
--> src/main.rs:20:13
|
20 | name.as_ptr() as *const c_void,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
|
= note: expected type *mut libc::c_void
found type *const libc::c_void

error: aborting due to 2 previous errors

For more information about this error, try rustc --explain E0308.
error: Could not compile sysctl-break.

To learn more, run the command again with --verbose.
$cargo +stable --version
cargo 1.33.0 (f099fe94b 2019-02-12)
$uname -a
Linux 3.10.0-693.2.2.el7.x86_64 #1 SMP Tue Sep 12 22:26:13 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

[gnzlbg]

Is there a version of libc that compiled that example for that target correctly?

[przygienda]

johalun/sysctl-rs#22 seems like crate was never tested on linux albeit I remember ages ago to have it working