1 #![cfg_attr(test, allow(dead_code))]
3 use self::imp::{drop_handler, make_handler};
5 pub use self::imp::cleanup;
6 pub use self::imp::init;
9 _data: *mut libc::c_void,
13 pub unsafe fn new() -> Handler {
17 fn null() -> Handler {
18 Handler { _data: crate::ptr::null_mut() }
22 impl Drop for Handler {
33 target_os = "dragonfly",
34 target_os = "freebsd",
35 target_os = "solaris",
36 target_os = "illumos",
48 use libc::{mmap, munmap};
49 use libc::{sigaction, sighandler_t, SA_ONSTACK, SA_SIGINFO, SIGBUS, SIG_DFL};
50 use libc::{sigaltstack, SIGSTKSZ, SS_DISABLE};
51 use libc::{MAP_ANON, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE, SIGSEGV};
53 use crate::sync::atomic::{AtomicBool, AtomicPtr, Ordering};
54 use crate::sys::unix::os::page_size;
55 use crate::sys_common::thread_info;
57 #[cfg(any(target_os = "linux", target_os = "android"))]
58 unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
61 a: [libc::c_int; 3], // si_signo, si_errno, si_code
62 si_addr: *mut libc::c_void,
65 (*(info as *const siginfo_t)).si_addr as usize
68 #[cfg(not(any(target_os = "linux", target_os = "android")))]
69 unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
70 (*info).si_addr as usize
73 // Signal handler for the SIGSEGV and SIGBUS handlers. We've got guard pages
74 // (unmapped pages) at the end of every thread's stack, so if a thread ends
75 // up running into the guard page it'll trigger this handler. We want to
76 // detect these cases and print out a helpful error saying that the stack
77 // has overflowed. All other signals, however, should go back to what they
78 // were originally supposed to do.
80 // This handler currently exists purely to print an informative message
81 // whenever a thread overflows its stack. We then abort to exit and
82 // indicate a crash, but to avoid a misleading SIGSEGV that might lead
83 // users to believe that unsafe code has accessed an invalid pointer; the
84 // SIGSEGV encountered when overflowing the stack is expected and
87 // If this is not a stack overflow, the handler un-registers itself and
88 // then returns (to allow the original signal to be delivered again).
89 // Returning from this kind of signal handler is technically not defined
90 // to work when reading the POSIX spec strictly, but in practice it turns
91 // out many large systems and all implementations allow returning from a
92 // signal handler to work. For a more detailed explanation see the
93 // comments on #26458.
94 unsafe extern "C" fn signal_handler(
96 info: *mut libc::siginfo_t,
97 _data: *mut libc::c_void,
99 let guard = thread_info::stack_guard().unwrap_or(0..0);
100 let addr = siginfo_si_addr(info);
102 // If the faulting address is within the guard page, then we print a
103 // message saying so and abort.
104 if guard.start <= addr && addr < guard.end {
106 "\nthread '{}' has overflowed its stack\n",
107 thread::current().name().unwrap_or("<unknown>")
109 rtabort!("stack overflow");
111 // Unregister ourselves by reverting back to the default behavior.
112 let mut action: sigaction = mem::zeroed();
113 action.sa_sigaction = SIG_DFL;
114 sigaction(signum, &action, ptr::null_mut());
116 // See comment above for why this function returns.
120 static MAIN_ALTSTACK: AtomicPtr<libc::c_void> = AtomicPtr::new(ptr::null_mut());
121 static NEED_ALTSTACK: AtomicBool = AtomicBool::new(false);
123 pub unsafe fn init() {
124 let mut action: sigaction = mem::zeroed();
125 for &signal in &[SIGSEGV, SIGBUS] {
126 sigaction(signal, ptr::null_mut(), &mut action);
127 // Configure our signal handler if one is not already set.
128 if action.sa_sigaction == SIG_DFL {
129 action.sa_flags = SA_SIGINFO | SA_ONSTACK;
130 action.sa_sigaction = signal_handler as sighandler_t;
131 sigaction(signal, &action, ptr::null_mut());
132 NEED_ALTSTACK.store(true, Ordering::Relaxed);
136 let handler = make_handler();
137 MAIN_ALTSTACK.store(handler._data, Ordering::Relaxed);
138 mem::forget(handler);
141 pub unsafe fn cleanup() {
142 Handler { _data: MAIN_ALTSTACK.load(Ordering::Relaxed) };
145 unsafe fn get_stackp() -> *mut libc::c_void {
146 // OpenBSD requires this flag for stack mapping
147 // otherwise the said mapping will fail as a no-op on most systems
148 // and has a different meaning on FreeBSD
149 #[cfg(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux",))]
150 let flags = MAP_PRIVATE | MAP_ANON | libc::MAP_STACK;
151 #[cfg(not(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux",)))]
152 let flags = MAP_PRIVATE | MAP_ANON;
154 mmap(ptr::null_mut(), SIGSTKSZ + page_size(), PROT_READ | PROT_WRITE, flags, -1, 0);
155 if stackp == MAP_FAILED {
156 panic!("failed to allocate an alternative stack: {}", io::Error::last_os_error());
158 let guard_result = libc::mprotect(stackp, page_size(), PROT_NONE);
159 if guard_result != 0 {
160 panic!("failed to set up alternative stack guard page: {}", io::Error::last_os_error());
162 stackp.add(page_size())
165 unsafe fn get_stack() -> libc::stack_t {
166 libc::stack_t { ss_sp: get_stackp(), ss_flags: 0, ss_size: SIGSTKSZ }
169 pub unsafe fn make_handler() -> Handler {
170 if !NEED_ALTSTACK.load(Ordering::Relaxed) {
171 return Handler::null();
173 let mut stack = mem::zeroed();
174 sigaltstack(ptr::null(), &mut stack);
175 // Configure alternate signal stack, if one is not already set.
176 if stack.ss_flags & SS_DISABLE != 0 {
178 sigaltstack(&stack, ptr::null_mut());
179 Handler { _data: stack.ss_sp as *mut libc::c_void }
185 pub unsafe fn drop_handler(handler: &mut Handler) {
186 if !handler._data.is_null() {
187 let stack = libc::stack_t {
188 ss_sp: ptr::null_mut(),
189 ss_flags: SS_DISABLE,
190 // Workaround for bug in macOS implementation of sigaltstack
191 // UNIX2003 which returns ENOMEM when disabling a stack while
192 // passing ss_size smaller than MINSIGSTKSZ. According to POSIX
193 // both ss_sp and ss_size should be ignored in this case.
196 sigaltstack(&stack, ptr::null_mut());
197 // We know from `get_stackp` that the alternate stack we installed is part of a mapping
198 // that started one page earlier, so walk back a page and unmap from there.
199 munmap(handler._data.sub(page_size()), SIGSTKSZ + page_size());
207 target_os = "dragonfly",
208 target_os = "freebsd",
209 target_os = "solaris",
210 target_os = "illumos",
211 target_os = "netbsd",
212 target_os = "openbsd",
215 pub unsafe fn init() {}
217 pub unsafe fn cleanup() {}
219 pub unsafe fn make_handler() -> super::Handler {
220 super::Handler::null()
223 pub unsafe fn drop_handler(_handler: &mut super::Handler) {}