library/std/src/rt.rs

   1 //! Runtime services
   2 //!
   3 //! The `rt` module provides a narrow set of runtime services,
   4 //! including the global heap (exported in `heap`) and unwinding and
   5 //! backtrace support. The APIs in this module are highly unstable,
   6 //! and should be considered as private implementation details for the
   7 //! time being.
   8
   9 #![unstable(
  10     feature = "rt",
  11     reason = "this public module should not exist and is highly likely \
  12               to disappear",
  13     issue = "none"
  14 )]
  15 #![doc(hidden)]
  16 #![deny(unsafe_op_in_unsafe_fn)]
  17 #![allow(unused_macros)]
  18
  19 use crate::ffi::CString;
  20
  21 // Re-export some of our utilities which are expected by other crates.
  22 pub use crate::panicking::{begin_panic, panic_count};
  23 pub use core::panicking::{panic_display, panic_fmt};
  24
  25 use crate::sync::Once;
  26 use crate::sys;
  27 use crate::sys_common::thread_info;
  28 use crate::thread::Thread;
  29
  30 // Prints to the "panic output", depending on the platform this may be:
  31 // - the standard error output
  32 // - some dedicated platform specific output
  33 // - nothing (so this macro is a no-op)
  34 macro_rules! rtprintpanic {
  35     ($($t:tt)*) => {
  36         if let Some(mut out) = crate::sys::stdio::panic_output() {
  37             let _ = crate::io::Write::write_fmt(&mut out, format_args!($($t)*));
  38         }
  39     }
  40 }
  41
  42 macro_rules! rtabort {
  43     ($($t:tt)*) => {
  44         {
  45             rtprintpanic!("fatal runtime error: {}\n", format_args!($($t)*));
  46             crate::sys::abort_internal();
  47         }
  48     }
  49 }
  50
  51 macro_rules! rtassert {
  52     ($e:expr) => {
  53         if !$e {
  54             rtabort!(concat!("assertion failed: ", stringify!($e)));
  55         }
  56     };
  57 }
  58
  59 macro_rules! rtunwrap {
  60     ($ok:ident, $e:expr) => {
  61         match $e {
  62             $ok(v) => v,
  63             ref err => {
  64                 let err = err.as_ref().map(drop); // map Ok/Some which might not be Debug
  65                 rtabort!(concat!("unwrap failed: ", stringify!($e), " = {:?}"), err)
  66             }
  67         }
  68     };
  69 }
  70
  71 // One-time runtime initialization.
  72 // Runs before `main`.
  73 // SAFETY: must be called only once during runtime initialization.
  74 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
  75 #[cfg_attr(test, allow(dead_code))]
  76 unsafe fn init(argc: isize, argv: *const *const u8) {
  77     unsafe {
  78         sys::init(argc, argv);
  79
  80         let main_guard = sys::thread::guard::init();
  81         // Next, set up the current Thread with the guard information we just
  82         // created. Note that this isn't necessary in general for new threads,
  83         // but we just do this to name the main thread and to give it correct
  84         // info about the stack bounds.
  85         let thread = Thread::new(Some(rtunwrap!(Ok, CString::new("main"))));
  86         thread_info::set(main_guard, thread);
  87     }
  88 }
  89
  90 // One-time runtime cleanup.
  91 // Runs after `main` or at program exit.
  92 // NOTE: this is not guaranteed to run, for example when the program aborts.
  93 pub(crate) fn cleanup() {
  94     static CLEANUP: Once = Once::new();
  95     CLEANUP.call_once(|| unsafe {
  96         // Flush stdout and disable buffering.
  97         crate::io::cleanup();
  98         // SAFETY: Only called once during runtime cleanup.
  99         sys::cleanup();
 100     });
 101 }
 102
 103 // To reduce the generated code of the new `lang_start`, this function is doing
 104 // the real work.
 105 #[cfg(not(test))]
 106 fn lang_start_internal(
 107     main: &(dyn Fn() -> i32 + Sync + crate::panic::RefUnwindSafe),
 108     argc: isize,
 109     argv: *const *const u8,
 110 ) -> Result<isize, !> {
 111     use crate::{mem, panic};
 112     let rt_abort = move |e| {
 113         mem::forget(e);
 114         rtabort!("initialization or cleanup bug");
 115     };
 116     // Guard against the code called by this function from unwinding outside of the Rust-controlled
 117     // code, which is UB. This is a requirement imposed by a combination of how the
 118     // `#[lang="start"]` attribute is implemented as well as by the implementation of the panicking
 119     // mechanism itself.
 120     //
 121     // There are a couple of instances where unwinding can begin. First is inside of the
 122     // `rt::init`, `rt::cleanup` and similar functions controlled by libstd. In those instances a
 123     // panic is a libstd implementation bug. A quite likely one too, as there isn't any way to
 124     // prevent libstd from accidentally introducing a panic to these functions. Another is from
 125     // user code from `main` or, more nefariously, as described in e.g. issue #86030.
 126     // SAFETY: Only called once during runtime initialization.
 127     panic::catch_unwind(move || unsafe { init(argc, argv) }).map_err(rt_abort)?;
 128     let ret_code = panic::catch_unwind(move || panic::catch_unwind(main).unwrap_or(101) as isize)
 129         .map_err(move |e| {
 130             mem::forget(e);
 131             rtabort!("drop of the panic payload panicked");
 132         });
 133     panic::catch_unwind(cleanup).map_err(rt_abort)?;
 134     ret_code
 135 }
 136
 137 #[cfg(not(test))]
 138 #[lang = "start"]
 139 fn lang_start<T: crate::process::Termination + 'static>(
 140     main: fn() -> T,
 141     argc: isize,
 142     argv: *const *const u8,
 143 ) -> isize {
 144     let Ok(v) = lang_start_internal(
 145         &move || crate::sys_common::backtrace::__rust_begin_short_backtrace(main).report().to_i32(),
 146         argc,
 147         argv,
 148     );
 149     v
 150 }