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",
47 use libc::{mmap, munmap};
48 use libc::{sigaction, sighandler_t, SA_ONSTACK, SA_SIGINFO, SIGBUS, SIG_DFL};
49 use libc::{sigaltstack, SIGSTKSZ, SS_DISABLE};
50 use libc::{MAP_ANON, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE, SIGSEGV};
52 use crate::sync::atomic::{AtomicBool, AtomicPtr, Ordering};
53 use crate::sys::unix::os::page_size;
54 use crate::sys_common::thread_info;
56 #[cfg(any(target_os = "linux", target_os = "android"))]
57 unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
60 a: [libc::c_int; 3], // si_signo, si_errno, si_code
61 si_addr: *mut libc::c_void,
64 (*(info as *const siginfo_t)).si_addr as usize
67 #[cfg(not(any(target_os = "linux", target_os = "android")))]
68 unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
69 (*info).si_addr as usize
72 // Signal handler for the SIGSEGV and SIGBUS handlers. We've got guard pages
73 // (unmapped pages) at the end of every thread's stack, so if a thread ends
74 // up running into the guard page it'll trigger this handler. We want to
75 // detect these cases and print out a helpful error saying that the stack
76 // has overflowed. All other signals, however, should go back to what they
77 // were originally supposed to do.
79 // This handler currently exists purely to print an informative message
80 // whenever a thread overflows its stack. We then abort to exit and
81 // indicate a crash, but to avoid a misleading SIGSEGV that might lead
82 // users to believe that unsafe code has accessed an invalid pointer; the
83 // SIGSEGV encountered when overflowing the stack is expected and
86 // If this is not a stack overflow, the handler un-registers itself and
87 // then returns (to allow the original signal to be delivered again).
88 // Returning from this kind of signal handler is technically not defined
89 // to work when reading the POSIX spec strictly, but in practice it turns
90 // out many large systems and all implementations allow returning from a
91 // signal handler to work. For a more detailed explanation see the
92 // comments on #26458.
93 unsafe extern "C" fn signal_handler(
95 info: *mut libc::siginfo_t,
96 _data: *mut libc::c_void,
98 use crate::sys_common::util::report_overflow;
100 let guard = thread_info::stack_guard().unwrap_or(0..0);
101 let addr = siginfo_si_addr(info);
103 // If the faulting address is within the guard page, then we print a
104 // message saying so and abort.
105 if guard.start <= addr && addr < guard.end {
107 rtabort!("stack overflow");
109 // Unregister ourselves by reverting back to the default behavior.
110 let mut action: sigaction = mem::zeroed();
111 action.sa_sigaction = SIG_DFL;
112 sigaction(signum, &action, ptr::null_mut());
114 // See comment above for why this function returns.
118 static MAIN_ALTSTACK: AtomicPtr<libc::c_void> = AtomicPtr::new(ptr::null_mut());
119 static NEED_ALTSTACK: AtomicBool = AtomicBool::new(false);
121 pub unsafe fn init() {
122 let mut action: sigaction = mem::zeroed();
123 for &signal in &[SIGSEGV, SIGBUS] {
124 sigaction(signal, ptr::null_mut(), &mut action);
125 // Configure our signal handler if one is not already set.
126 if action.sa_sigaction == SIG_DFL {
127 action.sa_flags = SA_SIGINFO | SA_ONSTACK;
128 action.sa_sigaction = signal_handler as sighandler_t;
129 sigaction(signal, &action, ptr::null_mut());
130 NEED_ALTSTACK.store(true, Ordering::Relaxed);
134 let handler = make_handler();
135 MAIN_ALTSTACK.store(handler._data, Ordering::Relaxed);
136 mem::forget(handler);
139 pub unsafe fn cleanup() {
140 Handler { _data: MAIN_ALTSTACK.load(Ordering::Relaxed) };
143 unsafe fn get_stackp() -> *mut libc::c_void {
146 SIGSTKSZ + page_size(),
147 PROT_READ | PROT_WRITE,
148 MAP_PRIVATE | MAP_ANON,
152 if stackp == MAP_FAILED {
153 panic!("failed to allocate an alternative stack: {}", io::Error::last_os_error());
155 let guard_result = libc::mprotect(stackp, page_size(), PROT_NONE);
156 if guard_result != 0 {
157 panic!("failed to set up alternative stack guard page: {}", io::Error::last_os_error());
159 stackp.add(page_size())
165 target_os = "freebsd",
166 target_os = "netbsd",
167 target_os = "openbsd",
168 target_os = "solaris",
169 target_os = "illumos"
171 unsafe fn get_stack() -> libc::stack_t {
172 libc::stack_t { ss_sp: get_stackp(), ss_flags: 0, ss_size: SIGSTKSZ }
175 #[cfg(target_os = "dragonfly")]
176 unsafe fn get_stack() -> libc::stack_t {
177 libc::stack_t { ss_sp: get_stackp() as *mut i8, ss_flags: 0, ss_size: SIGSTKSZ }
180 pub unsafe fn make_handler() -> Handler {
181 if !NEED_ALTSTACK.load(Ordering::Relaxed) {
182 return Handler::null();
184 let mut stack = mem::zeroed();
185 sigaltstack(ptr::null(), &mut stack);
186 // Configure alternate signal stack, if one is not already set.
187 if stack.ss_flags & SS_DISABLE != 0 {
189 sigaltstack(&stack, ptr::null_mut());
190 Handler { _data: stack.ss_sp as *mut libc::c_void }
196 pub unsafe fn drop_handler(handler: &mut Handler) {
197 if !handler._data.is_null() {
198 let stack = libc::stack_t {
199 ss_sp: ptr::null_mut(),
200 ss_flags: SS_DISABLE,
201 // Workaround for bug in macOS implementation of sigaltstack
202 // UNIX2003 which returns ENOMEM when disabling a stack while
203 // passing ss_size smaller than MINSIGSTKSZ. According to POSIX
204 // both ss_sp and ss_size should be ignored in this case.
207 sigaltstack(&stack, ptr::null_mut());
208 // We know from `get_stackp` that the alternate stack we installed is part of a mapping
209 // that started one page earlier, so walk back a page and unmap from there.
210 munmap(handler._data.sub(page_size()), SIGSTKSZ + page_size());
218 target_os = "dragonfly",
219 target_os = "freebsd",
220 target_os = "solaris",
221 target_os = "illumos",
222 target_os = "netbsd",
223 target_os = "openbsd",
226 pub unsafe fn init() {}
228 pub unsafe fn cleanup() {}
230 pub unsafe fn make_handler() -> super::Handler {
231 super::Handler::null()
234 pub unsafe fn drop_handler(_handler: &mut super::Handler) {}