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Diffstat (limited to 'src/runtime.rs')
| -rw-r--r-- | src/runtime.rs | 581 |
1 files changed, 581 insertions, 0 deletions
diff --git a/src/runtime.rs b/src/runtime.rs new file mode 100644 index 0000000..bd3eed2 --- /dev/null +++ b/src/runtime.rs @@ -0,0 +1,581 @@ +//! Experimental low-level implementation details for libc-like runtime +//! libraries such as [Origin]. +//! +//! Do not use the functions in this module unless you've read all of their +//! code. They don't always behave the same way as functions with similar names +//! in `libc`. Sometimes information about the differences is included in the +//! Linux documentation under “C library/kernel differences” sections. And, if +//! there is a libc in the process, these functions may have surprising +//! interactions with it. +//! +//! These functions are for implementing thread-local storage (TLS), managing +//! threads, loaded libraries, and other process-wide resources. Most of +//! `rustix` doesn't care about what other libraries are linked into the +//! program or what they're doing, but the features in this module generally +//! can only be used by one entity within a process. +//! +//! The API for these functions is not stable, and this module is +//! `doc(hidden)`. +//! +//! [Origin]: https://github.com/sunfishcode/origin#readme +//! +//! # Safety +//! +//! This module is intended to be used for implementing a runtime library such +//! as libc. Use of these features for any other purpose is likely to create +//! serious problems. +#![allow(unsafe_code)] + +use crate::backend; +#[cfg(linux_raw)] +use crate::ffi::CStr; +#[cfg(linux_raw)] +#[cfg(feature = "fs")] +use crate::fs::AtFlags; +#[cfg(linux_raw)] +use crate::io; +#[cfg(linux_raw)] +use crate::pid::Pid; +#[cfg(linux_raw)] +#[cfg(feature = "fs")] +use backend::fd::AsFd; +#[cfg(linux_raw)] +use core::ffi::c_void; + +#[cfg(linux_raw)] +pub use crate::signal::Signal; + +/// `sigaction` +#[cfg(linux_raw)] +pub type Sigaction = linux_raw_sys::general::kernel_sigaction; + +/// `stack_t` +#[cfg(linux_raw)] +pub type Stack = linux_raw_sys::general::stack_t; + +/// `sigset_t` +#[cfg(linux_raw)] +pub type Sigset = linux_raw_sys::general::kernel_sigset_t; + +/// `siginfo_t` +#[cfg(linux_raw)] +pub type Siginfo = linux_raw_sys::general::siginfo_t; + +pub use crate::timespec::{Nsecs, Secs, Timespec}; + +/// `SIG_*` constants for use with [`sigprocmask`]. +#[cfg(linux_raw)] +#[repr(u32)] +pub enum How { + /// `SIG_BLOCK` + BLOCK = linux_raw_sys::general::SIG_BLOCK, + + /// `SIG_UNBLOCK` + UNBLOCK = linux_raw_sys::general::SIG_UNBLOCK, + + /// `SIG_SETMASK` + SETMASK = linux_raw_sys::general::SIG_SETMASK, +} + +#[cfg(target_arch = "x86")] +#[inline] +pub unsafe fn set_thread_area(u_info: &mut UserDesc) -> io::Result<()> { + backend::runtime::syscalls::tls::set_thread_area(u_info) +} + +#[cfg(target_arch = "arm")] +#[inline] +pub unsafe fn arm_set_tls(data: *mut c_void) -> io::Result<()> { + backend::runtime::syscalls::tls::arm_set_tls(data) +} + +/// `prctl(PR_SET_FS, data)`—Set the x86-64 `fs` register. +/// +/// # Safety +/// +/// This is a very low-level feature for implementing threading libraries. +/// See the references links above. +#[cfg(target_arch = "x86_64")] +#[inline] +pub unsafe fn set_fs(data: *mut c_void) { + backend::runtime::syscalls::tls::set_fs(data) +} + +/// Set the x86-64 thread ID address. +/// +/// # Safety +/// +/// This is a very low-level feature for implementing threading libraries. +/// See the references links above. +#[inline] +pub unsafe fn set_tid_address(data: *mut c_void) -> Pid { + backend::runtime::syscalls::tls::set_tid_address(data) +} + +#[cfg(linux_raw)] +#[cfg(target_arch = "x86")] +pub use backend::runtime::tls::UserDesc; + +/// `syscall(SYS_exit, status)`—Exit the current thread. +/// +/// # Safety +/// +/// This is a very low-level feature for implementing threading libraries. +#[inline] +pub unsafe fn exit_thread(status: i32) -> ! { + backend::runtime::syscalls::tls::exit_thread(status) +} + +/// Exit all the threads in the current process' thread group. +/// +/// This is equivalent to `_exit` and `_Exit` in libc. +/// +/// This does not call any `__cxa_atexit`, `atexit`, or any other destructors. +/// Most programs should use [`std::process::exit`] instead of calling this +/// directly. +/// +/// # References +/// - [POSIX `_Exit`] +/// - [Linux `exit_group`] +/// - [Linux `_Exit`] +/// +/// [POSIX `_Exit`]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/_Exit.html +/// [Linux `exit_group`]: https://man7.org/linux/man-pages/man2/exit_group.2.html +/// [Linux `_Exit`]: https://man7.org/linux/man-pages/man2/_Exit.2.html +#[doc(alias = "_exit")] +#[doc(alias = "_Exit")] +#[inline] +pub fn exit_group(status: i32) -> ! { + backend::runtime::syscalls::exit_group(status) +} + +/// `EXIT_SUCCESS` for use with [`exit_group`]. +/// +/// # References +/// - [POSIX] +/// - [Linux] +/// +/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdlib.h.html +/// [Linux]: https://man7.org/linux/man-pages/man3/exit.3.html +pub const EXIT_SUCCESS: i32 = backend::c::EXIT_SUCCESS; + +/// `EXIT_FAILURE` for use with [`exit_group`]. +/// +/// # References +/// - [POSIX] +/// - [Linux] +/// +/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdlib.h.html +/// [Linux]: https://man7.org/linux/man-pages/man3/exit.3.html +pub const EXIT_FAILURE: i32 = backend::c::EXIT_FAILURE; + +/// Return fields from the main executable segment headers ("phdrs") relevant +/// to initializing TLS provided to the program at startup. +/// +/// `addr` will always be non-null, even when the TLS data is absent, so that +/// the `addr` and `file_size` parameters are suitable for creating a slice +/// with `slice::from_raw_parts`. +#[inline] +pub fn startup_tls_info() -> StartupTlsInfo { + backend::runtime::tls::startup_tls_info() +} + +/// `(getauxval(AT_PHDR), getauxval(AT_PHENT), getauxval(AT_PHNUM))`—Returns +/// the address, ELF segment header size, and number of ELF segment headers for +/// the main executable. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man3/getauxval.3.html +#[inline] +pub fn exe_phdrs() -> (*const c_void, usize, usize) { + backend::param::auxv::exe_phdrs() +} + +/// `getauxval(AT_ENTRY)`—Returns the address of the program entrypoint. +/// +/// Most code interested in the program entrypoint address should instead use a +/// symbol reference to `_start`. That will be properly PC-relative or +/// relocated if needed, and will come with appropriate pointer type and +/// pointer provenance. +/// +/// This function is intended only for use in code that implements those +/// relocations, to compute the ASLR offset. It has type `usize`, so it doesn't +/// carry any provenance, and it shouldn't be used to dereference memory. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man3/getauxval.3.html +#[inline] +pub fn entry() -> usize { + backend::param::auxv::entry() +} + +/// `getauxval(AT_RANDOM)`—Returns the address of 16 pseudorandom bytes. +/// +/// These bytes are for use by libc. For anything else, use the `rand` crate. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man3/getauxval.3.html +#[inline] +pub fn random() -> *const [u8; 16] { + backend::param::auxv::random() +} + +#[cfg(linux_raw)] +pub use backend::runtime::tls::StartupTlsInfo; + +/// `fork()`—Creates a new process by duplicating the calling process. +/// +/// On success, the pid of the child process is returned in the parent, and +/// `None` is returned in the child. +/// +/// Unlike its POSIX and libc counterparts, this `fork` does not invoke any +/// handlers (such as those registered with `pthread_atfork`). +/// +/// The program environment in the child after a `fork` and before an `execve` +/// is very special. All code that executes in this environment must avoid: +/// +/// - Acquiring any other locks that are held in other threads on the parent +/// at the time of the `fork`, as the child only contains one thread, and +/// attempting to acquire such locks will deadlock (though this is [not +/// considered unsafe]). +/// +/// - Performing any dynamic allocation using the global allocator, since +/// global allocators may use locks to ensure thread safety, and their locks +/// may not be released in the child process, so attempts to allocate may +/// deadlock (as described in the previous point). +/// +/// - Accessing any external state which the parent assumes it has exclusive +/// access to, such as a file protected by a file lock, as this could +/// corrupt the external state. +/// +/// - Accessing any random-number-generator state inherited from the parent, +/// as the parent may have the same state and generate the same random +/// numbers, which may violate security invariants. +/// +/// - Accessing any thread runtime state, since this function does not update +/// the thread id in the thread runtime, so thread runtime functions could +/// cause undefined behavior. +/// +/// - Accessing any memory shared with the parent, such as a [`MAP_SHARED`] +/// mapping, even with anonymous or [`memfd_create`] mappings, as this could +/// cause undefined behavior. +/// +/// - Calling any C function which isn't known to be [async-signal-safe], as +/// that could cause undefined behavior. The extent to which this also +/// applies to Rust functions is unclear at this time. +/// +/// - And more. +/// +/// # Safety +/// +/// The child must avoid accessing any memory shared with the parent in a +/// way that invokes undefined behavior. It must avoid accessing any threading +/// runtime functions in a way that invokes undefined behavior. And it must +/// avoid invoking any undefined behavior through any function that is not +/// guaranteed to be async-signal-safe. But, what does async-signal-safe even +/// mean in a Rust program? This documentation does not have all the answers. +/// +/// So you're on your own. And on top of all the troubles with `fork` in +/// general, this wrapper implementation is highly experimental. +/// +/// # References +/// - [POSIX] +/// - [Linux] +/// +/// # Literary interlude +/// +/// > Do not jump on ancient uncles. +/// > Do not yell at average mice. +/// > Do not wear a broom to breakfast. +/// > Do not ask a snake’s advice. +/// > Do not bathe in chocolate pudding. +/// > Do not talk to bearded bears. +/// > Do not smoke cigars on sofas. +/// > Do not dance on velvet chairs. +/// > Do not take a whale to visit +/// > Russell’s mother’s cousin’s yacht. +/// > And whatever else you do do +/// > It is better you +/// > Do not. +/// +/// - “Rules”, by Karla Kuskin +/// +/// [`MAP_SHARED`]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/mmap.html +/// [not considered unsafe]: https://doc.rust-lang.org/reference/behavior-not-considered-unsafe.html#deadlocks +/// [`memfd_create`]: https://man7.org/linux/man-pages/man2/memfd_create.2.html +/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html +/// [Linux]: https://man7.org/linux/man-pages/man2/fork.2.html +/// [async-signal-safe]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_04_03 +pub unsafe fn fork() -> io::Result<Fork> { + backend::runtime::syscalls::fork() +} + +/// Regular Unix `fork` doesn't tell the child its own PID because it assumes +/// the child can just do `getpid`. That's true, but it's more fun if it +/// doesn't have to. +pub enum Fork { + Child(Pid), + Parent(Pid), +} + +/// `execveat(dirfd, path.as_c_str(), argv, envp, flags)`—Execute a new +/// command using the current process. +/// +/// # Safety +/// +/// The `argv` and `envp` pointers must point to NUL-terminated arrays, and +/// their contents must be pointers to NUL-terminated byte arrays. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man2/execveat.2.html +#[inline] +#[cfg(feature = "fs")] +#[cfg_attr(doc_cfg, doc(cfg(feature = "fs")))] +pub unsafe fn execveat<Fd: AsFd>( + dirfd: Fd, + path: &CStr, + argv: *const *const u8, + envp: *const *const u8, + flags: AtFlags, +) -> io::Errno { + backend::runtime::syscalls::execveat(dirfd.as_fd(), path, argv, envp, flags) +} + +/// `execve(path.as_c_str(), argv, envp)`—Execute a new command using the +/// current process. +/// +/// # Safety +/// +/// The `argv` and `envp` pointers must point to NUL-terminated arrays, and +/// their contents must be pointers to NUL-terminated byte arrays. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man2/execve.2.html +#[inline] +pub unsafe fn execve(path: &CStr, argv: *const *const u8, envp: *const *const u8) -> io::Errno { + backend::runtime::syscalls::execve(path, argv, envp) +} + +/// `sigaction(signal, &new, &old)`—Modify or query a signal handler. +/// +/// # Safety +/// +/// You're on your own. And on top of all the troubles with signal handlers, +/// this implementation is highly experimental. Even further, it differs from +/// the libc `sigaction` in several non-obvious and unsafe ways. +/// +/// # References +/// - [POSIX] +/// - [Linux] +/// +/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigaction.html +/// [Linux]: https://man7.org/linux/man-pages/man2/sigaction.2.html +#[inline] +pub unsafe fn sigaction(signal: Signal, new: Option<Sigaction>) -> io::Result<Sigaction> { + backend::runtime::syscalls::sigaction(signal, new) +} + +/// `sigaltstack(new, old)`—Modify or query a signal stack. +/// +/// # Safety +/// +/// You're on your own. And on top of all the troubles with signal handlers, +/// this implementation is highly experimental. +/// +/// # References +/// - [POSIX] +/// - [Linux] +/// +/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigaltstack.html +/// [Linux]: https://man7.org/linux/man-pages/man2/sigaltstack.2.html +#[inline] +pub unsafe fn sigaltstack(new: Option<Stack>) -> io::Result<Stack> { + backend::runtime::syscalls::sigaltstack(new) +} + +/// `tkill(tid, sig)`—Send a signal to a thread. +/// +/// # Safety +/// +/// You're on your own. And on top of all the troubles with signal handlers, +/// this implementation is highly experimental. The warning about the hazard +/// of recycled thread ID's applies. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man2/tkill.2.html +#[inline] +pub unsafe fn tkill(tid: Pid, sig: Signal) -> io::Result<()> { + backend::runtime::syscalls::tkill(tid, sig) +} + +/// `sigprocmask(how, set, oldset)`—Adjust the process signal mask. +/// +/// # Safety +/// +/// You're on your own. And on top of all the troubles with signal handlers, +/// this implementation is highly experimental. Even further, it differs from +/// the libc `sigprocmask` in several non-obvious and unsafe ways. +/// +/// # References +/// - [Linux `sigprocmask`] +/// - [Linux `pthread_sigmask`] +/// +/// [Linux `sigprocmask`]: https://man7.org/linux/man-pages/man2/sigprocmask.2.html +/// [Linux `pthread_sigmask`]: https://man7.org/linux/man-pages/man3/pthread_sigmask.3.html +#[inline] +#[doc(alias = "pthread_sigmask")] +pub unsafe fn sigprocmask(how: How, set: Option<&Sigset>) -> io::Result<Sigset> { + backend::runtime::syscalls::sigprocmask(how, set) +} + +/// `sigpending()`—Query the pending signals. +/// +/// # References +/// - [Linux `sigpending`] +/// +/// [Linux `sigpending`]: https://man7.org/linux/man-pages/man2/sigpending.2.html +#[inline] +pub fn sigpending() -> Sigset { + backend::runtime::syscalls::sigpending() +} + +/// `sigsuspend(set)`—Suspend the calling thread and wait for signals. +/// +/// # References +/// - [Linux `sigsuspend`] +/// +/// [Linux `sigsuspend`]: https://man7.org/linux/man-pages/man2/sigsuspend.2.html +#[inline] +pub fn sigsuspend(set: &Sigset) -> io::Result<()> { + backend::runtime::syscalls::sigsuspend(set) +} + +/// `sigwait(set)`—Wait for signals. +/// +/// # Safety +/// +/// If code elsewhere in the process is depending on delivery of a signal to +/// prevent it from executing some code, this could cause it to miss that +/// signal and execute that code. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man3/sigwait.3.html +#[inline] +pub unsafe fn sigwait(set: &Sigset) -> io::Result<Signal> { + backend::runtime::syscalls::sigwait(set) +} + +/// `sigwaitinfo(set)`—Wait for signals, returning a [`Siginfo`]. +/// +/// # Safety +/// +/// If code elsewhere in the process is depending on delivery of a signal to +/// prevent it from executing some code, this could cause it to miss that +/// signal and execute that code. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man2/sigwaitinfo.2.html +#[inline] +pub unsafe fn sigwaitinfo(set: &Sigset) -> io::Result<Siginfo> { + backend::runtime::syscalls::sigwaitinfo(set) +} + +/// `sigtimedwait(set)`—Wait for signals, optionally with a timeout. +/// +/// # Safety +/// +/// If code elsewhere in the process is depending on delivery of a signal to +/// prevent it from executing some code, this could cause it to miss that +/// signal and execute that code. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man2/sigtimedwait.2.html +#[inline] +pub unsafe fn sigtimedwait(set: &Sigset, timeout: Option<Timespec>) -> io::Result<Siginfo> { + backend::runtime::syscalls::sigtimedwait(set, timeout) +} + +/// `getauxval(AT_SECURE)`—Returns the Linux “secure execution” mode. +/// +/// Return a boolean value indicating whether “secure execution” mode was +/// requested, due to the process having elevated privileges. This includes +/// whether the `AT_SECURE` AUX value is set, and whether the initial real UID +/// and GID differ from the initial effective UID and GID. +/// +/// The meaning of “secure execution” mode is beyond the scope of this +/// comment. +/// +/// # References +/// - [Linux] +/// +/// [Linux]: https://man7.org/linux/man-pages/man3/getauxval.3.html +#[cfg(any( + linux_raw, + any( + all(target_os = "android", target_pointer_width = "64"), + target_os = "linux", + ) +))] +#[inline] +pub fn linux_secure() -> bool { + backend::param::auxv::linux_secure() +} + +/// `brk(addr)`—Change the location of the “program break”. +/// +/// # Safety +/// +/// This is not identical to `brk` in libc. libc `brk` may have bookkeeping +/// that needs to be kept up to date that this doesn't keep up to date, so +/// don't use it unless you are implementing libc. +#[cfg(linux_raw)] +#[inline] +pub unsafe fn brk(addr: *mut c_void) -> io::Result<*mut c_void> { + backend::runtime::syscalls::brk(addr) +} + +/// `__SIGRTMIN`—The start of the realtime signal range. +/// +/// This is the raw `SIGRTMIN` value from the OS, which is not the same as the +/// `SIGRTMIN` macro provided by libc. Don't use this unless you are +/// implementing libc. +#[cfg(linux_raw)] +pub const SIGRTMIN: u32 = linux_raw_sys::general::SIGRTMIN; + +/// `__SIGRTMAX`—The last of the realtime signal range. +/// +/// This is the raw `SIGRTMAX` value from the OS, which is not the same as the +/// `SIGRTMAX` macro provided by libc. Don't use this unless you are +/// implementing libc. +#[cfg(linux_raw)] +pub const SIGRTMAX: u32 = { + // Use the actual `SIGRTMAX` value on platforms which define it. + #[cfg(not(any(target_arch = "arm", target_arch = "x86", target_arch = "x86_64")))] + { + linux_raw_sys::general::SIGRTMAX + } + + // On platfoms that don't, derive it from `_NSIG`. + #[cfg(any(target_arch = "arm", target_arch = "x86", target_arch = "x86_64"))] + { + linux_raw_sys::general::_NSIG - 1 + } +}; |