wasmtime/runtime/vm/sys/unix/
signals.rs

1//! Trap handling on Unix based on POSIX signals.
2
3use crate::prelude::*;
4use crate::runtime::vm::traphandlers::{TrapRegisters, TrapTest, tls};
5use std::cell::RefCell;
6use std::io;
7use std::mem;
8use std::ptr::{self, null_mut};
9use wasmtime_unwinder::Handler;
10
11/// Function which may handle custom signals while processing traps.
12pub type SignalHandler =
13    Box<dyn Fn(libc::c_int, *const libc::siginfo_t, *const libc::c_void) -> bool + Send + Sync>;
14
15const UNINIT_SIGACTION: libc::sigaction = unsafe { mem::zeroed() };
16static mut PREV_SIGSEGV: libc::sigaction = UNINIT_SIGACTION;
17static mut PREV_SIGBUS: libc::sigaction = UNINIT_SIGACTION;
18static mut PREV_SIGILL: libc::sigaction = UNINIT_SIGACTION;
19static mut PREV_SIGFPE: libc::sigaction = UNINIT_SIGACTION;
20
21pub struct TrapHandler;
22
23impl TrapHandler {
24    /// Installs all trap handlers.
25    ///
26    /// # Unsafety
27    ///
28    /// This function is unsafe because it's not safe to call concurrently and
29    /// it's not safe to call if the trap handlers have already been initialized
30    /// for this process.
31    pub unsafe fn new(macos_use_mach_ports: bool) -> TrapHandler {
32        // Either mach ports shouldn't be in use or we shouldn't be on macOS,
33        // otherwise the `machports.rs` module should be used instead.
34        assert!(!macos_use_mach_ports || !cfg!(target_vendor = "apple"));
35
36        foreach_handler(|slot, signal| {
37            let mut handler: libc::sigaction = unsafe { mem::zeroed() };
38            // The flags here are relatively careful, and they are...
39            //
40            // SA_SIGINFO gives us access to information like the program
41            // counter from where the fault happened.
42            //
43            // SA_ONSTACK allows us to handle signals on an alternate stack,
44            // so that the handler can run in response to running out of
45            // stack space on the main stack. Rust installs an alternate
46            // stack with sigaltstack, so we rely on that.
47            //
48            // SA_NODEFER allows us to reenter the signal handler if we
49            // crash while handling the signal, and fall through to the
50            // Breakpad handler by testing handlingSegFault.
51            handler.sa_flags = libc::SA_SIGINFO | libc::SA_NODEFER | libc::SA_ONSTACK;
52            handler.sa_sigaction = (trap_handler as *const ()).addr();
53            unsafe {
54                libc::sigemptyset(&mut handler.sa_mask);
55                if libc::sigaction(signal, &handler, slot) != 0 {
56                    panic!(
57                        "unable to install signal handler: {}",
58                        io::Error::last_os_error(),
59                    );
60                }
61            }
62        });
63
64        TrapHandler
65    }
66
67    pub fn validate_config(&self, macos_use_mach_ports: bool) {
68        assert!(!macos_use_mach_ports || !cfg!(target_vendor = "apple"));
69    }
70}
71
72fn foreach_handler(mut f: impl FnMut(*mut libc::sigaction, i32)) {
73    // Allow handling OOB with signals on all architectures
74    f(&raw mut PREV_SIGSEGV, libc::SIGSEGV);
75
76    // Handle `unreachable` instructions which execute `ud2` right now
77    f(&raw mut PREV_SIGILL, libc::SIGILL);
78
79    // x86 and s390x use SIGFPE to report division by zero
80    if cfg!(target_arch = "x86_64") || cfg!(target_arch = "s390x") {
81        f(&raw mut PREV_SIGFPE, libc::SIGFPE);
82    }
83
84    // Sometimes we need to handle SIGBUS too:
85    // - On Darwin, guard page accesses are raised as SIGBUS.
86    if cfg!(target_vendor = "apple") || cfg!(target_os = "freebsd") {
87        f(&raw mut PREV_SIGBUS, libc::SIGBUS);
88    }
89
90    // TODO(#1980): x86-32, if we support it, will also need a SIGFPE handler.
91    // TODO(#1173): ARM32, if we support it, will also need a SIGBUS handler.
92}
93
94impl Drop for TrapHandler {
95    fn drop(&mut self) {
96        unsafe {
97            foreach_handler(|slot, signal| {
98                let mut prev: libc::sigaction = mem::zeroed();
99
100                // Restore the previous handler that this signal had.
101                if libc::sigaction(signal, slot, &mut prev) != 0 {
102                    eprintln!(
103                        "unable to reinstall signal handler: {}",
104                        io::Error::last_os_error(),
105                    );
106                    libc::abort();
107                }
108
109                // If our trap handler wasn't currently listed for this process
110                // then that's a problem because we have just corrupted the
111                // signal handler state and don't know how to remove ourselves
112                // from the signal handling state. Inform the user of this and
113                // abort the process.
114                if prev.sa_sigaction != (trap_handler as *const ()).addr() {
115                    eprintln!(
116                        "
117Wasmtime's signal handler was not the last signal handler to be installed
118in the process so it's not certain how to unload signal handlers. In this
119situation the Engine::unload_process_handlers API is not applicable and requires
120perhaps initializing libraries in a different order. The process will be aborted
121now.
122"
123                    );
124                    libc::abort();
125                }
126            });
127        }
128    }
129}
130
131unsafe extern "C" fn trap_handler(
132    signum: libc::c_int,
133    siginfo: *mut libc::siginfo_t,
134    context: *mut libc::c_void,
135) {
136    let previous = match signum {
137        libc::SIGSEGV => &raw const PREV_SIGSEGV,
138        libc::SIGBUS => &raw const PREV_SIGBUS,
139        libc::SIGFPE => &raw const PREV_SIGFPE,
140        libc::SIGILL => &raw const PREV_SIGILL,
141        _ => panic!("unknown signal: {signum}"),
142    };
143    let handled = tls::with(|info| {
144        // If no wasm code is executing, we don't handle this as a wasm
145        // trap.
146        let info = match info {
147            Some(info) => info,
148            None => return false,
149        };
150
151        // If we hit an exception while handling a previous trap, that's
152        // quite bad, so bail out and let the system handle this
153        // recursive segfault.
154        //
155        // Otherwise flag ourselves as handling a trap, do the trap
156        // handling, and reset our trap handling flag. Then we figure
157        // out what to do based on the result of the trap handling.
158        let faulting_addr = match signum {
159            libc::SIGSEGV | libc::SIGBUS => unsafe { Some((*siginfo).si_addr() as usize) },
160            _ => None,
161        };
162        let regs = unsafe { get_trap_registers(context, signum) };
163        let test = info.test_if_trap(regs, faulting_addr, |handler| {
164            handler(signum, siginfo, context)
165        });
166
167        // Figure out what to do based on the result of this handling of
168        // the trap. Note that our sentinel value of 1 means that the
169        // exception was handled by a custom exception handler, so we
170        // keep executing.
171        match test {
172            TrapTest::NotWasm => {
173                if let Some(faulting_addr) = faulting_addr {
174                    let range = unsafe { &info.vm_store_context.get().as_ref().async_guard_range };
175                    if range.start.addr() <= faulting_addr && faulting_addr < range.end.addr() {
176                        abort_stack_overflow();
177                    }
178                }
179                false
180            }
181            TrapTest::HandledByEmbedder => true,
182            TrapTest::Trap(handler) => {
183                unsafe {
184                    store_handler_in_ucontext(context, &handler);
185                }
186                true
187            }
188        }
189    });
190
191    if handled {
192        return;
193    }
194
195    unsafe { delegate_signal_to_previous_handler(previous, signum, siginfo, context) }
196}
197
198pub unsafe fn delegate_signal_to_previous_handler(
199    previous: *const libc::sigaction,
200    signum: libc::c_int,
201    siginfo: *mut libc::siginfo_t,
202    context: *mut libc::c_void,
203) {
204    // This signal is not for any compiled wasm code we expect, so we
205    // need to forward the signal to the next handler. If there is no
206    // next handler (SIG_IGN or SIG_DFL), then it's time to crash. To do
207    // this, we set the signal back to its original disposition and
208    // return. This will cause the faulting op to be re-executed which
209    // will crash in the normal way. If there is a next handler, call
210    // it. It will either crash synchronously, fix up the instruction
211    // so that execution can continue and return, or trigger a crash by
212    // returning the signal to it's original disposition and returning.
213    unsafe {
214        let previous = *previous;
215        if previous.sa_flags & libc::SA_SIGINFO != 0 {
216            mem::transmute::<
217                usize,
218                extern "C" fn(libc::c_int, *mut libc::siginfo_t, *mut libc::c_void),
219            >(previous.sa_sigaction)(signum, siginfo, context)
220        } else if previous.sa_sigaction == libc::SIG_DFL || previous.sa_sigaction == libc::SIG_IGN {
221            libc::sigaction(signum, &previous as *const _, ptr::null_mut());
222        } else {
223            mem::transmute::<usize, extern "C" fn(libc::c_int)>(previous.sa_sigaction)(signum)
224        }
225    }
226}
227
228pub fn abort_stack_overflow() -> ! {
229    unsafe {
230        let msg = "execution on async fiber has overflowed its stack";
231        libc::write(libc::STDERR_FILENO, msg.as_ptr().cast(), msg.len());
232        libc::abort();
233    }
234}
235
236#[allow(
237    clippy::cast_possible_truncation,
238    reason = "too fiddly to handle and wouldn't help much anyway"
239)]
240unsafe fn get_trap_registers(cx: *mut libc::c_void, _signum: libc::c_int) -> TrapRegisters {
241    cfg_select! {
242        all(any(target_os = "linux", target_os = "android", target_os = "illumos"), target_arch = "x86_64") => {
243            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
244            TrapRegisters {
245                pc: cx.uc_mcontext.gregs[libc::REG_RIP as usize] as usize,
246                fp: cx.uc_mcontext.gregs[libc::REG_RBP as usize] as usize,
247            }
248        }
249        all(target_os = "linux", target_arch = "x86") => {
250            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
251            TrapRegisters {
252                pc: cx.uc_mcontext.gregs[libc::REG_EIP as usize] as usize,
253                fp: cx.uc_mcontext.gregs[libc::REG_EBP as usize] as usize,
254            }
255        }
256        all(any(target_os = "linux", target_os = "android"), target_arch = "aarch64") => {
257            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
258            TrapRegisters {
259                pc: cx.uc_mcontext.pc as usize,
260                fp: cx.uc_mcontext.regs[29] as usize,
261            }
262        }
263        all(target_os = "linux", target_arch = "s390x") => {
264            // On s390x, SIGILL and SIGFPE are delivered with the PSW address
265            // pointing *after* the faulting instruction, while SIGSEGV and
266            // SIGBUS are delivered with the PSW address pointing *to* the
267            // faulting instruction.  To handle this, the code generator registers
268            // any trap that results in one of "late" signals on the last byte
269            // of the instruction, and any trap that results in one of the "early"
270            // signals on the first byte of the instruction (as usual).  This
271            // means we simply need to decrement the reported PSW address by
272            // one in the case of a "late" signal here to ensure we always
273            // correctly find the associated trap handler.
274            let trap_offset = match _signum {
275                libc::SIGILL | libc::SIGFPE => 1,
276                _ => 0,
277            };
278            unsafe {
279                let cx = &*(cx as *const libc::ucontext_t);
280                TrapRegisters {
281                    pc: (cx.uc_mcontext.psw.addr - trap_offset) as usize,
282                    fp: *(cx.uc_mcontext.gregs[15] as *const usize),
283                }
284            }
285        }
286        all(target_vendor = "apple", target_arch = "x86_64") => {
287            unsafe {
288                let cx = &*(cx as *const libc::ucontext_t);
289                TrapRegisters {
290                    pc: (*cx.uc_mcontext).__ss.__rip as usize,
291                    fp: (*cx.uc_mcontext).__ss.__rbp as usize,
292                }
293            }
294        }
295        all(target_vendor = "apple", target_arch = "aarch64") => {
296            unsafe {
297                let cx = &*(cx as *const libc::ucontext_t);
298                TrapRegisters {
299                    pc: (*cx.uc_mcontext).__ss.__pc as usize,
300                    fp: (*cx.uc_mcontext).__ss.__fp as usize,
301                }
302            }
303        }
304        all(target_os = "freebsd", target_arch = "x86_64") => {
305            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
306            TrapRegisters {
307                pc: cx.uc_mcontext.mc_rip as usize,
308                fp: cx.uc_mcontext.mc_rbp as usize,
309            }
310        }
311        all(target_os = "linux", target_arch = "riscv64") => {
312            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
313            TrapRegisters {
314                pc: cx.uc_mcontext.__gregs[libc::REG_PC] as usize,
315                fp: cx.uc_mcontext.__gregs[libc::REG_S0] as usize,
316            }
317        }
318        all(target_os = "freebsd", target_arch = "aarch64") => {
319            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
320            TrapRegisters {
321                pc: cx.uc_mcontext.mc_gpregs.gp_elr as usize,
322                fp: cx.uc_mcontext.mc_gpregs.gp_x[29] as usize,
323            }
324        }
325        all(target_os = "openbsd", target_arch = "x86_64") => {
326            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
327            TrapRegisters {
328                pc: cx.sc_rip as usize,
329                fp: cx.sc_rbp as usize,
330            }
331        }
332        all(target_os = "linux", target_arch = "arm") => {
333            let cx = unsafe { &*(cx as *const libc::ucontext_t) };
334            TrapRegisters {
335                pc: cx.uc_mcontext.arm_pc as usize,
336                fp: cx.uc_mcontext.arm_fp as usize,
337            }
338        }
339        _ => {
340            compile_error!("unsupported platform");
341            panic!();
342        }
343    }
344}
345
346/// Updates the siginfo context stored in `cx` to resume to `handler` up on
347/// resumption while returning from the signal handler.
348unsafe fn store_handler_in_ucontext(cx: *mut libc::c_void, handler: &Handler) {
349    cfg_select! {
350        all(any(target_os = "linux", target_os = "android", target_os = "illumos"), target_arch = "x86_64") => {
351            let cx = unsafe { cx.cast::<libc::ucontext_t>().as_mut().unwrap() };
352            cx.uc_mcontext.gregs[libc::REG_RIP as usize] = handler.pc as _;
353            cx.uc_mcontext.gregs[libc::REG_RSP as usize] = handler.sp as _;
354            cx.uc_mcontext.gregs[libc::REG_RBP as usize] = handler.fp as _;
355            cx.uc_mcontext.gregs[libc::REG_RAX as usize] = 0;
356            cx.uc_mcontext.gregs[libc::REG_RDX as usize] = 0;
357        }
358        all(any(target_os = "linux", target_os = "android"), target_arch = "aarch64") => {
359            let cx = unsafe { cx.cast::<libc::ucontext_t>().as_mut().unwrap() };
360            cx.uc_mcontext.pc = handler.pc as _;
361            cx.uc_mcontext.sp = handler.sp as _;
362            cx.uc_mcontext.regs[29] = handler.fp as _;
363            cx.uc_mcontext.regs[0] = 0;
364            cx.uc_mcontext.regs[1] = 0;
365        }
366        all(target_os = "linux", target_arch = "s390x") => {
367            let cx = unsafe { cx.cast::<libc::ucontext_t>().as_mut().unwrap() };
368            cx.uc_mcontext.psw.addr = handler.pc as _;
369            cx.uc_mcontext.gregs[15] = handler.sp as _;
370            cx.uc_mcontext.gregs[6] = 0;
371            cx.uc_mcontext.gregs[7] = 0;
372        }
373        all(target_vendor = "apple", target_arch = "x86_64") => {
374            unsafe {
375                let cx = cx.cast::<libc::ucontext_t>().as_mut().unwrap();
376                let cx = cx.uc_mcontext.as_mut().unwrap();
377                cx.__ss.__rip = handler.pc as _;
378                cx.__ss.__rsp = handler.sp as _;
379                cx.__ss.__rbp = handler.fp as _;
380                cx.__ss.__rax = 0;
381                cx.__ss.__rdx = 0;
382            }
383        }
384        all(target_vendor = "apple", target_arch = "aarch64") => {
385            unsafe {
386                let cx = cx.cast::<libc::ucontext_t>().as_mut().unwrap();
387                let cx = cx.uc_mcontext.as_mut().unwrap();
388                cx.__ss.__pc = handler.pc as _;
389                cx.__ss.__sp = handler.sp as _;
390                cx.__ss.__fp = handler.fp as _;
391                cx.__ss.__x[0] = 0;
392                cx.__ss.__x[1] = 0;
393            }
394        }
395        all(target_os = "freebsd", target_arch = "x86_64") => {
396            let cx = unsafe { cx.cast::<libc::ucontext_t>().as_mut().unwrap() };
397            cx.uc_mcontext.mc_rip = handler.pc as _;
398            cx.uc_mcontext.mc_rbp = handler.fp as _;
399            cx.uc_mcontext.mc_rsp = handler.sp as _;
400            cx.uc_mcontext.mc_rax = 0;
401            cx.uc_mcontext.mc_rdx = 0;
402        }
403        all(target_os = "freebsd", target_arch = "aarch64") => {
404            let cx = unsafe { cx.cast::<libc::ucontext_t>().as_mut().unwrap() };
405            cx.uc_mcontext.mc_gpregs.gp_elr = handler.pc as _;
406            cx.uc_mcontext.mc_gpregs.gp_sp = handler.sp as _;
407            cx.uc_mcontext.mc_gpregs.gp_x[29] = handler.fp as _;
408            cx.uc_mcontext.mc_gpregs.gp_x[0] = 0;
409            cx.uc_mcontext.mc_gpregs.gp_x[1] = 0;
410        }
411        all(target_os = "openbsd", target_arch = "x86_64") => {
412            let cx = unsafe { cx.cast::<libc::ucontext_t>().as_mut().unwrap() };
413            cx.sc_rip = handler.pc as _;
414            cx.sc_rbp = handler.fp as _;
415            cx.sc_rsp = handler.sp as _;
416            cx.sc_rax = 0;
417            cx.sc_rdx = 0;
418        }
419        all(target_os = "linux", target_arch = "riscv64") => {
420            let cx = unsafe { cx.cast::<libc::ucontext_t>().as_mut().unwrap() };
421            cx.uc_mcontext.__gregs[libc::REG_PC] = handler.pc as _;
422            cx.uc_mcontext.__gregs[libc::REG_S0] = handler.fp as _;
423            cx.uc_mcontext.__gregs[libc::REG_SP] = handler.sp as _;
424            cx.uc_mcontext.__gregs[libc::REG_A0] = 0;
425            cx.uc_mcontext.__gregs[libc::REG_A0 + 1] = 0;
426        }
427        _ => {
428            compile_error!("unsupported platform");
429            panic!();
430        }
431    }
432}
433
434/// A function for registering a custom alternate signal stack (sigaltstack).
435///
436/// Rust's libstd installs an alternate stack with size `SIGSTKSZ`, which is not
437/// always large enough for our signal handling code. Override it by creating
438/// and registering our own alternate stack that is large enough and has a guard
439/// page.
440///
441/// Note that one might reasonably ask why do this at all? Why not remove
442/// `SA_ONSTACK` from our signal handlers entirely? The basic reason for that is
443/// because we want to print a message on stack overflow. The Rust standard
444/// library will print this message by default and by us overriding the
445/// `SIGSEGV` handler above we're now sharing responsibility for that as well.
446/// We must have `SA_ONSTACK` to even attempt to being able to printing this
447/// message, and so we leave it turned on. Wasmtime will determine a stack
448/// overflow fault isn't caused by wasm and then forward to libstd's signal
449/// handler which will actually print-and-abort.
450///
451/// Another reasonable question might be why we need to increase the size of the
452/// sigaltstack at all? This is something which we may want to reconsider in the
453/// future. For now it helps keep debug builds working which consume more stack
454/// when handling normal wasm out-of-bounds and faults. Perhaps in the future we
455/// could optimize this more or maybe even do something clever like lazily
456/// allocate the sigaltstack on the fault itself. (e.g. trampoline from a tiny
457/// stack to the "big stack" during a wasm fault or something like that)
458#[cold]
459pub fn lazy_per_thread_init() {
460    // This is a load-bearing requirement to keep address-sanitizer working and
461    // prevent crashes during fuzzing. The general idea here is that we skip the
462    // sigaltstack setup below entirely on asan builds, aka fuzzing. The exact
463    // reason for this is not entirely known, but the closest guess we have at
464    // this time is something like:
465    //
466    // * ASAN builds intercept mmap/munmap to keep track of what's going on.
467    // * The sigaltstack below registers a TLS destructor for when the current
468    //   thread exits to deallocate the stack.
469    // * ASAN looks to also have TLS destructors for its own internal state.
470    // * The current assumption is that the order of these TLS destructors can
471    //   cause corruption in ASAN state where if we run after asan's destructor
472    //   it may intercept munmap and then asan doesn't know it's been
473    //   de-initialized yet.
474    //
475    // The reproduction of this involved a standalone project built with
476    // `-Zsanitizer=address` where internally it would spawn two threads. Each
477    // thread would build a "hello world" module and then one of the threads
478    // would execute a noop exported function. If this was run thousands of
479    // times in a loop in the same process it would eventually crash under asan.
480    //
481    // It's notably not quite so simple as frobbing TLS destructors. There's
482    // clearly something else going on with ASAN state internally which we don't
483    // fully understand at this time. An attempt to make a standalone C++
484    // reproduction, for example, was not successful. In lieu of that the best
485    // we have for now is to disable our custom and larger sigaltstack in asan
486    // builds.
487    //
488    // The exact source was
489    // https://gist.github.com/alexcrichton/6815a5d57a3c5ca94a8d816a9fcc91af for
490    // future reference if necessary.
491    if cfg!(asan) {
492        return;
493    }
494
495    // This thread local is purely used to register a `Stack` to get deallocated
496    // when the thread exists. Otherwise this function is only ever called at
497    // most once per-thread.
498    std::thread_local! {
499        static STACK: RefCell<Option<Stack>> = const { RefCell::new(None) };
500    }
501
502    /// The size of the sigaltstack (not including the guard, which will be
503    /// added). Make this large enough to run our signal handlers.
504    ///
505    /// The main current requirement of the signal handler in terms of stack
506    /// space is that `malloc`/`realloc` are called to create a `Backtrace` of
507    /// wasm frames.
508    ///
509    /// Historically this was 16k. Turns out jemalloc requires more than 16k of
510    /// stack space in debug mode, so this was bumped to 64k.
511    const MIN_STACK_SIZE: usize = 64 * 4096;
512
513    struct Stack {
514        mmap_ptr: *mut libc::c_void,
515        mmap_size: usize,
516    }
517
518    return STACK.with(|s| {
519        *s.borrow_mut() = unsafe { allocate_sigaltstack() };
520    });
521
522    unsafe fn allocate_sigaltstack() -> Option<Stack> {
523        // Check to see if the existing sigaltstack, if it exists, is big
524        // enough. If so we don't need to allocate our own.
525        let mut old_stack = unsafe { mem::zeroed() };
526        let r = unsafe { libc::sigaltstack(ptr::null(), &mut old_stack) };
527        assert_eq!(
528            r,
529            0,
530            "learning about sigaltstack failed: {}",
531            io::Error::last_os_error()
532        );
533        if old_stack.ss_flags & libc::SS_DISABLE == 0 && old_stack.ss_size >= MIN_STACK_SIZE {
534            return None;
535        }
536
537        // ... but failing that we need to allocate our own, so do all that
538        // here.
539        let page_size = crate::runtime::vm::host_page_size();
540        let guard_size = page_size;
541        let alloc_size = guard_size + MIN_STACK_SIZE;
542
543        let ptr = unsafe {
544            rustix::mm::mmap_anonymous(
545                null_mut(),
546                alloc_size,
547                rustix::mm::ProtFlags::empty(),
548                rustix::mm::MapFlags::PRIVATE,
549            )
550            .expect("failed to allocate memory for sigaltstack")
551        };
552
553        // Prepare the stack with readable/writable memory and then register it
554        // with `sigaltstack`.
555        let stack_ptr = (ptr as usize + guard_size) as *mut std::ffi::c_void;
556        unsafe {
557            rustix::mm::mprotect(
558                stack_ptr,
559                MIN_STACK_SIZE,
560                rustix::mm::MprotectFlags::READ | rustix::mm::MprotectFlags::WRITE,
561            )
562            .expect("mprotect to configure memory for sigaltstack failed");
563        }
564        let new_stack = libc::stack_t {
565            ss_sp: stack_ptr,
566            ss_flags: 0,
567            ss_size: MIN_STACK_SIZE,
568        };
569        let r = unsafe { libc::sigaltstack(&new_stack, ptr::null_mut()) };
570        assert_eq!(
571            r,
572            0,
573            "registering new sigaltstack failed: {}",
574            io::Error::last_os_error()
575        );
576
577        Some(Stack {
578            mmap_ptr: ptr,
579            mmap_size: alloc_size,
580        })
581    }
582
583    impl Drop for Stack {
584        fn drop(&mut self) {
585            unsafe {
586                // Before unmapping our memory make sure that it's no longer
587                // listed as our sigaltstack. While it's pretty unlikely we'll
588                // fault during thread teardown we don't want to make things
589                // worse by then additionally using an unmapped stack.
590                //
591                // Also this seems to help with pre-LLVM-23 asan configuration,
592                // see #13857 for some more details.
593                let new_stack = libc::stack_t {
594                    ss_sp: ptr::null_mut(),
595                    ss_flags: libc::SS_DISABLE,
596                    ss_size: MIN_STACK_SIZE,
597                };
598                let r = libc::sigaltstack(&new_stack, ptr::null_mut());
599                debug_assert_eq!(
600                    r,
601                    0,
602                    "registering new sigaltstack failed: {}",
603                    io::Error::last_os_error()
604                );
605
606                // Deallocate the stack memory now that nothing should be using
607                // it.
608                let r = rustix::mm::munmap(self.mmap_ptr, self.mmap_size);
609                debug_assert!(r.is_ok(), "munmap failed during thread shutdown");
610            }
611        }
612    }
613}
wasmtime/runtime/vm/sys/unix/signals.rs

wasmtime/runtime/vm/sys/unix/
signals.rs
