linux-syscalls 0.4.0

A library to easily invoke linux system calls.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144

use core::{
    ptr,
    sync::atomic::{AtomicU32, Ordering},
};

use crate::{syscall, Errno, Sysno};

const FUTEX_WAIT_BITSET: i32 = 9;
const FUTEX_WAKE: i32 = 1;
const FUTEX_PRIVATE_FLAG: i32 = 128;

const INITIAL: u32 = 0x0;
const RUNNING: u32 = 0x1;
const COMPLETE: u32 = 0x2;
const PANICKED: u32 = 0xffff_ffff;

static mut LOCK: AtomicU32 = AtomicU32::new(INITIAL);

unsafe fn real_init(env: *const ()) {
    crate::env::aux::init(env);
    #[cfg(target_arch = "powerpc64")]
    crate::arch::init();
    crate::env::kernel::init();
    crate::env::vdso::init();
    #[cfg(not(target_arch = "powerpc64"))]
    crate::arch::init();
}

unsafe fn aux_from_environ(env: *const *const u8) -> *const () {
    let mut p = env;
    while !(*p).is_null() {
        p = p.add(1);
    }
    p.add(1) as *mut ()
}

#[cfg(any(doc, not(feature = "bare")))]
unsafe fn aux_ptr() -> *const () {
    extern "C" {
        #[cfg(any(target_env = "gnu", target_env = "musl"))]
        static __environ: *const *const u8;
        #[cfg(not(any(target_env = "gnu", target_env = "musl")))]
        static environ: *const *const u8;
    }
    #[cfg(not(any(target_env = "gnu", target_env = "musl")))]
    let env = environ;
    #[cfg(any(target_env = "gnu", target_env = "musl"))]
    let env = __environ;
    aux_from_environ(env)
}

/// Initialize the environment for the library.
/// It's recommended to call it before anything else in the main function.
#[cfg(any(doc, not(feature = "bare")))]
#[cfg_attr(docs_rs, doc(cfg(not(feature = "bare"))))]
pub fn init() {
    unsafe { inner_init(aux_ptr()) }
}

#[cfg(any(doc, feature = "bare"))]
/// Initialize library from the environment list pointer (`char **envp`).
/// It's recommended to call it before anything else in the main function.
///
/// # Safety
///
/// Dealing with pointers is unsafe by definition.
#[cfg_attr(docs_rs, doc(cfg(feature = "bare")))]
#[allow(clippy::not_unsafe_ptr_arg_deref)]
pub unsafe fn init_from_environ(env: *const *const u8) {
    inner_init(aux_from_environ(env))
}

#[cfg(any(doc, feature = "bare"))]
/// Initialize library from arguments count and arguments list (`int argc, char **argv`).
/// It's recommended to call it before anything else in the main function.
///
/// # Safety
///
/// Dealing with pointers is unsafe by definition.
#[allow(clippy::not_unsafe_ptr_arg_deref)]
#[cfg_attr(docs_rs, doc(cfg(feature = "bare")))]
pub unsafe fn init_from_args(argc: usize, argv: *const *const u8) {
    inner_init(aux_from_environ(argv.add(argc)))
}

#[cfg(any(doc, feature = "bare"))]
/// Initialize library from auxv pointer.
/// It's recommended to call it before anything else in the main function.
///
/// # Safety
///
/// Dealing with pointers is unsafe by definition.
#[cfg_attr(docs_rs, doc(cfg(feature = "bare")))]
pub unsafe fn init_from_auxv(auxv: *const core::ffi::c_void) {
    inner_init(auxv.cast())
}

unsafe fn inner_init(auxv: *const ()) {
    loop {
        match LOCK.compare_exchange_weak(INITIAL, RUNNING, Ordering::Acquire, Ordering::Relaxed) {
            Ok(_) => {
                let _guard = Guard;
                real_init(auxv);
                LOCK.store(COMPLETE, Ordering::Release);
                syscall!(
                    Sysno::futex,
                    ptr::addr_of!(LOCK),
                    FUTEX_WAKE | FUTEX_PRIVATE_FLAG,
                    0x7fffffff,
                )
                .unwrap();
                break;
            }
            Err(x) if x == RUNNING => loop {
                let res = syscall!(
                    Sysno::futex,
                    ptr::addr_of!(LOCK),
                    FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG,
                    x,
                    core::ptr::null::<u8>(),
                    core::ptr::null::<u32>(),
                    !0u32,
                );
                if res != Err(Errno::EINTR) {
                    break;
                }
            },
            Err(x) if x == PANICKED => panic!("syscall locker has been poisoned"),
            Err(_) => break,
        }
    }
}

struct Guard;

impl Drop for Guard {
    fn drop(&mut self) {
        unsafe {
            if LOCK.load(Ordering::Relaxed) == RUNNING {
                LOCK.store(PANICKED, Ordering::Relaxed);
            }
        }
    }
}