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#![cfg_attr(test, allow(dead_code))]
use self::imp::{drop_handler, make_handler};
pub use self::imp::cleanup;
pub use self::imp::init;
pub struct Handler {
_data: *mut libc::c_void,
}
impl Handler {
pub unsafe fn new() -> Handler {
make_handler()
}
fn null() -> Handler {
Handler { _data: crate::ptr::null_mut() }
}
}
impl Drop for Handler {
fn drop(&mut self) {
unsafe {
drop_handler(self);
}
}
}
#[cfg(any(
target_os = "linux",
target_os = "macos",
target_os = "dragonfly",
target_os = "freebsd",
target_os = "solaris",
target_os = "illumos",
all(target_os = "netbsd", not(target_vendor = "rumprun")),
target_os = "openbsd"
))]
mod imp {
use super::Handler;
use crate::mem;
use crate::ptr;
use libc::MAP_FAILED;
use libc::{mmap, munmap};
use libc::{sigaction, sighandler_t, SA_ONSTACK, SA_SIGINFO, SIGBUS, SIG_DFL};
use libc::{sigaltstack, SIGSTKSZ, SS_DISABLE};
use libc::{MAP_ANON, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE, SIGSEGV};
use crate::sys::unix::os::page_size;
use crate::sys_common::thread_info;
#[cfg(any(target_os = "linux", target_os = "android"))]
unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
#[repr(C)]
struct siginfo_t {
a: [libc::c_int; 3], // si_signo, si_errno, si_code
si_addr: *mut libc::c_void,
}
(*(info as *const siginfo_t)).si_addr as usize
}
#[cfg(not(any(target_os = "linux", target_os = "android")))]
unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
(*info).si_addr as usize
}
// Signal handler for the SIGSEGV and SIGBUS handlers. We've got guard pages
// (unmapped pages) at the end of every thread's stack, so if a thread ends
// up running into the guard page it'll trigger this handler. We want to
// detect these cases and print out a helpful error saying that the stack
// has overflowed. All other signals, however, should go back to what they
// were originally supposed to do.
//
// This handler currently exists purely to print an informative message
// whenever a thread overflows its stack. We then abort to exit and
// indicate a crash, but to avoid a misleading SIGSEGV that might lead
// users to believe that unsafe code has accessed an invalid pointer; the
// SIGSEGV encountered when overflowing the stack is expected and
// well-defined.
//
// If this is not a stack overflow, the handler un-registers itself and
// then returns (to allow the original signal to be delivered again).
// Returning from this kind of signal handler is technically not defined
// to work when reading the POSIX spec strictly, but in practice it turns
// out many large systems and all implementations allow returning from a
// signal handler to work. For a more detailed explanation see the
// comments on #26458.
unsafe extern "C" fn signal_handler(
signum: libc::c_int,
info: *mut libc::siginfo_t,
_data: *mut libc::c_void,
) {
use crate::sys_common::util::report_overflow;
let guard = thread_info::stack_guard().unwrap_or(0..0);
let addr = siginfo_si_addr(info);
// If the faulting address is within the guard page, then we print a
// message saying so and abort.
if guard.start <= addr && addr < guard.end {
report_overflow();
rtabort!("stack overflow");
} else {
// Unregister ourselves by reverting back to the default behavior.
let mut action: sigaction = mem::zeroed();
action.sa_sigaction = SIG_DFL;
sigaction(signum, &action, ptr::null_mut());
// See comment above for why this function returns.
}
}
static mut MAIN_ALTSTACK: *mut libc::c_void = ptr::null_mut();
static mut NEED_ALTSTACK: bool = false;
pub unsafe fn init() {
let mut action: sigaction = mem::zeroed();
for &signal in &[SIGSEGV, SIGBUS] {
sigaction(signal, ptr::null_mut(), &mut action);
// Configure our signal handler if one is not already set.
if action.sa_sigaction == SIG_DFL {
action.sa_flags = SA_SIGINFO | SA_ONSTACK;
action.sa_sigaction = signal_handler as sighandler_t;
sigaction(signal, &action, ptr::null_mut());
NEED_ALTSTACK = true;
}
}
let handler = make_handler();
MAIN_ALTSTACK = handler._data;
mem::forget(handler);
}
pub unsafe fn cleanup() {
Handler { _data: MAIN_ALTSTACK };
}
unsafe fn get_stackp() -> *mut libc::c_void {
let stackp = mmap(
ptr::null_mut(),
SIGSTKSZ + page_size(),
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON,
-1,
0,
);
if stackp == MAP_FAILED {
panic!("failed to allocate an alternative stack");
}
let guard_result = libc::mprotect(stackp, page_size(), PROT_NONE);
if guard_result != 0 {
panic!("failed to set up alternative stack guard page");
}
stackp.add(page_size())
}
#[cfg(any(
target_os = "linux",
target_os = "macos",
target_os = "freebsd",
target_os = "netbsd",
target_os = "openbsd",
target_os = "solaris",
target_os = "illumos"
))]
unsafe fn get_stack() -> libc::stack_t {
libc::stack_t { ss_sp: get_stackp(), ss_flags: 0, ss_size: SIGSTKSZ }
}
#[cfg(target_os = "dragonfly")]
unsafe fn get_stack() -> libc::stack_t {
libc::stack_t { ss_sp: get_stackp() as *mut i8, ss_flags: 0, ss_size: SIGSTKSZ }
}
pub unsafe fn make_handler() -> Handler {
if !NEED_ALTSTACK {
return Handler::null();
}
let mut stack = mem::zeroed();
sigaltstack(ptr::null(), &mut stack);
// Configure alternate signal stack, if one is not already set.
if stack.ss_flags & SS_DISABLE != 0 {
stack = get_stack();
sigaltstack(&stack, ptr::null_mut());
Handler { _data: stack.ss_sp as *mut libc::c_void }
} else {
Handler::null()
}
}
pub unsafe fn drop_handler(handler: &mut Handler) {
if !handler._data.is_null() {
let stack = libc::stack_t {
ss_sp: ptr::null_mut(),
ss_flags: SS_DISABLE,
// Workaround for bug in macOS implementation of sigaltstack
// UNIX2003 which returns ENOMEM when disabling a stack while
// passing ss_size smaller than MINSIGSTKSZ. According to POSIX
// both ss_sp and ss_size should be ignored in this case.
ss_size: SIGSTKSZ,
};
sigaltstack(&stack, ptr::null_mut());
// We know from `get_stackp` that the alternate stack we installed is part of a mapping
// that started one page earlier, so walk back a page and unmap from there.
munmap(handler._data.sub(page_size()), SIGSTKSZ + page_size());
}
}
}
#[cfg(not(any(
target_os = "linux",
target_os = "macos",
target_os = "dragonfly",
target_os = "freebsd",
target_os = "solaris",
target_os = "illumos",
all(target_os = "netbsd", not(target_vendor = "rumprun")),
target_os = "openbsd"
)))]
mod imp {
pub unsafe fn init() {}
pub unsafe fn cleanup() {}
pub unsafe fn make_handler() -> super::Handler {
super::Handler::null()
}
pub unsafe fn drop_handler(_handler: &mut super::Handler) {}
}