wasmtime_internal_unwinder/arch/
mod.rs

1//! Architecture-specific runtime support corresponding to details of
2//! Cranelift codegen or ABI support.
3//!
4//! This crate houses any architecture-specific tidbits required when
5//! building a runtime that executes Cranelift-produced code.
6//!
7//! All architectures have the same interface when exposed to the rest of the
8//! crate.
9
10cfg_if::cfg_if! {
11    if #[cfg(target_arch = "x86_64")] {
12        mod x86;
13        use x86 as imp;
14    } else if #[cfg(target_arch = "aarch64")] {
15        mod aarch64;
16        use aarch64 as imp;
17    } else if #[cfg(target_arch = "s390x")] {
18        mod s390x;
19        use s390x as imp;
20    } else if #[cfg(target_arch = "riscv64")] {
21        mod riscv64;
22        use riscv64 as imp;
23    }
24}
25
26// Re re-export functions from the `imp` module with one set of `pub
27// use` declarations here so we can share doc-comments.
28
29cfg_if::cfg_if! {
30    if #[cfg(any(
31        target_arch = "x86_64",
32        target_arch = "aarch64",
33        target_arch = "s390x",
34        target_arch = "riscv64"
35    ))] {
36        /// Get the current stack pointer (at the time this function is
37        /// executing). This may be used to check, e.g., approximate space
38        /// remaining on a stack, but cannot be relied upon for anything exact
39        /// because the stack pointer from *within this function* is read and
40        /// the frame is later popped.
41        pub use imp::get_stack_pointer;
42
43        impl crate::Handler {
44            /// Resume execution at the given PC, SP, and FP, with the given
45            /// payload values, according to the tail-call ABI's exception
46            /// scheme. Note that this scheme does not restore any other
47            /// registers, so the given state is all that we need.
48            ///
49            /// # Safety
50            ///
51            /// This method requires:
52            ///
53            /// - the `sp` and `fp` to correspond to an active stack frame
54            ///   (above the current function), in code using Cranelift's
55            ///   `tail` calling convention.
56            ///
57            /// - The `pc` to correspond to a `try_call` handler
58            ///   destination, as emitted in Cranelift metadata, or
59            ///   otherwise a target that is expecting the tail-call ABI's
60            ///   exception ABI.
61            ///
62            /// - The Rust frames between the unwind destination and this
63            ///   frame to be unwind-safe: that is, they cannot have `Drop`
64            ///   handlers for which safety requires that they run.
65            ///
66            /// - The Cranelift-generated `try_call` that we're unwinding to was
67            ///   invoking the callee with the `tail` calling convention.
68            pub unsafe fn resume_tailcc(
69                &self,
70                payload1: usize,
71                payload2: usize,
72            ) -> ! {
73                // Without this ASAN seems to nondeterministically trigger an
74                // internal assertion when running tests with threads. Not entirely
75                // clear what's going on here but it seems related to the fact that
76                // there's Rust code on the stack which is never cleaned up due to
77                // the jump out of `imp::resume_to_exception_handler`.
78                //
79                // This function is documented as something that should be called to
80                // clean up the entire thread's shadow memory and stack which isn't
81                // exactly what we want but this at least seems to resolve ASAN
82                // issues for now. Probably a heavy hammer but better than false
83                // positives I suppose...
84                #[cfg(asan)]
85                {
86                    unsafe extern "C" {
87                        fn __asan_handle_no_return();
88                    }
89                    unsafe {
90                        __asan_handle_no_return();
91                    }
92                }
93                unsafe {
94                    imp::resume_to_exception_handler(self.pc, self.sp, self.fp, payload1, payload2)
95                }
96            }
97        }
98
99        /// Get the return address in the function at the next-older
100        /// frame from the given FP.
101        ///
102        /// # Safety
103        ///
104        /// - Requires that `fp` is a valid frame-pointer value for an
105        ///   active stack frame (above the current function), in code
106        ///   using Cranelift's `tail` calling convention.
107        use imp::get_next_older_pc_from_fp;
108
109        /// The offset of the saved old-FP value in a frame, from the
110        /// location pointed to by a given FP.
111        const NEXT_OLDER_FP_FROM_FP_OFFSET: usize = imp::NEXT_OLDER_FP_FROM_FP_OFFSET;
112
113        /// The offset of the next older SP value, from the value of a
114        /// given FP.
115        const NEXT_OLDER_SP_FROM_FP_OFFSET: usize = imp::NEXT_OLDER_SP_FROM_FP_OFFSET;
116
117        /// Assert that the given `fp` is aligned as expected by the
118        /// host platform's implementation of the Cranelift tail-call
119        /// ABI.
120        use imp::assert_fp_is_aligned;
121
122        /// If we have the above host-specific implementations, we can
123        /// implement `Unwind`.
124        pub struct UnwindHost;
125
126        unsafe impl crate::stackwalk::Unwind for UnwindHost {
127            fn next_older_fp_from_fp_offset(&self) -> usize {
128                NEXT_OLDER_FP_FROM_FP_OFFSET
129            }
130            fn next_older_sp_from_fp_offset(&self) -> usize {
131                NEXT_OLDER_SP_FROM_FP_OFFSET
132            }
133            unsafe fn get_next_older_pc_from_fp(&self, fp: usize) -> usize {
134                unsafe {
135                    get_next_older_pc_from_fp(fp)
136                }
137            }
138            fn assert_fp_is_aligned(&self, fp: usize) {
139                assert_fp_is_aligned(fp)
140            }
141        }
142    }
143}
wasmtime_internal_unwinder/arch/mod.rs

wasmtime_internal_unwinder/arch/
mod.rs
