miri/shims/
native_lib.rs

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1//! Implements calling functions from a native library.
2use std::ops::Deref;
3
4use libffi::high::call as ffi;
5use libffi::low::CodePtr;
6use rustc_abi::{BackendRepr, HasDataLayout, Size};
7use rustc_middle::mir::interpret::Pointer;
8use rustc_middle::ty::{self as ty, IntTy, UintTy};
9use rustc_span::Symbol;
10
11use crate::*;
12
13impl<'tcx> EvalContextExtPriv<'tcx> for crate::MiriInterpCx<'tcx> {}
14trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
15    /// Call native host function and return the output as an immediate.
16    fn call_native_with_args<'a>(
17        &mut self,
18        link_name: Symbol,
19        dest: &MPlaceTy<'tcx>,
20        ptr: CodePtr,
21        libffi_args: Vec<libffi::high::Arg<'a>>,
22    ) -> InterpResult<'tcx, ImmTy<'tcx>> {
23        let this = self.eval_context_mut();
24
25        // Call the function (`ptr`) with arguments `libffi_args`, and obtain the return value
26        // as the specified primitive integer type
27        let scalar = match dest.layout.ty.kind() {
28            // ints
29            ty::Int(IntTy::I8) => {
30                // Unsafe because of the call to native code.
31                // Because this is calling a C function it is not necessarily sound,
32                // but there is no way around this and we've checked as much as we can.
33                let x = unsafe { ffi::call::<i8>(ptr, libffi_args.as_slice()) };
34                Scalar::from_i8(x)
35            }
36            ty::Int(IntTy::I16) => {
37                let x = unsafe { ffi::call::<i16>(ptr, libffi_args.as_slice()) };
38                Scalar::from_i16(x)
39            }
40            ty::Int(IntTy::I32) => {
41                let x = unsafe { ffi::call::<i32>(ptr, libffi_args.as_slice()) };
42                Scalar::from_i32(x)
43            }
44            ty::Int(IntTy::I64) => {
45                let x = unsafe { ffi::call::<i64>(ptr, libffi_args.as_slice()) };
46                Scalar::from_i64(x)
47            }
48            ty::Int(IntTy::Isize) => {
49                let x = unsafe { ffi::call::<isize>(ptr, libffi_args.as_slice()) };
50                Scalar::from_target_isize(x.try_into().unwrap(), this)
51            }
52            // uints
53            ty::Uint(UintTy::U8) => {
54                let x = unsafe { ffi::call::<u8>(ptr, libffi_args.as_slice()) };
55                Scalar::from_u8(x)
56            }
57            ty::Uint(UintTy::U16) => {
58                let x = unsafe { ffi::call::<u16>(ptr, libffi_args.as_slice()) };
59                Scalar::from_u16(x)
60            }
61            ty::Uint(UintTy::U32) => {
62                let x = unsafe { ffi::call::<u32>(ptr, libffi_args.as_slice()) };
63                Scalar::from_u32(x)
64            }
65            ty::Uint(UintTy::U64) => {
66                let x = unsafe { ffi::call::<u64>(ptr, libffi_args.as_slice()) };
67                Scalar::from_u64(x)
68            }
69            ty::Uint(UintTy::Usize) => {
70                let x = unsafe { ffi::call::<usize>(ptr, libffi_args.as_slice()) };
71                Scalar::from_target_usize(x.try_into().unwrap(), this)
72            }
73            // Functions with no declared return type (i.e., the default return)
74            // have the output_type `Tuple([])`.
75            ty::Tuple(t_list) if t_list.is_empty() => {
76                unsafe { ffi::call::<()>(ptr, libffi_args.as_slice()) };
77                return interp_ok(ImmTy::uninit(dest.layout));
78            }
79            ty::RawPtr(..) => {
80                let x = unsafe { ffi::call::<*const ()>(ptr, libffi_args.as_slice()) };
81                let ptr = Pointer::new(Provenance::Wildcard, Size::from_bytes(x.addr()));
82                Scalar::from_pointer(ptr, this)
83            }
84            _ => throw_unsup_format!("unsupported return type for native call: {:?}", link_name),
85        };
86        interp_ok(ImmTy::from_scalar(scalar, dest.layout))
87    }
88
89    /// Get the pointer to the function of the specified name in the shared object file,
90    /// if it exists. The function must be in the shared object file specified: we do *not*
91    /// return pointers to functions in dependencies of the library.  
92    fn get_func_ptr_explicitly_from_lib(&mut self, link_name: Symbol) -> Option<CodePtr> {
93        let this = self.eval_context_mut();
94        // Try getting the function from the shared library.
95        // On windows `_lib_path` will be unused, hence the name starting with `_`.
96        let (lib, _lib_path) = this.machine.native_lib.as_ref().unwrap();
97        let func: libloading::Symbol<'_, unsafe extern "C" fn()> = unsafe {
98            match lib.get(link_name.as_str().as_bytes()) {
99                Ok(x) => x,
100                Err(_) => {
101                    return None;
102                }
103            }
104        };
105
106        // FIXME: this is a hack!
107        // The `libloading` crate will automatically load system libraries like `libc`.
108        // On linux `libloading` is based on `dlsym`: https://docs.rs/libloading/0.7.3/src/libloading/os/unix/mod.rs.html#202
109        // and `dlsym`(https://linux.die.net/man/3/dlsym) looks through the dependency tree of the
110        // library if it can't find the symbol in the library itself.
111        // So, in order to check if the function was actually found in the specified
112        // `machine.external_so_lib` we need to check its `dli_fname` and compare it to
113        // the specified SO file path.
114        // This code is a reimplementation of the mechanism for getting `dli_fname` in `libloading`,
115        // from: https://docs.rs/libloading/0.7.3/src/libloading/os/unix/mod.rs.html#411
116        // using the `libc` crate where this interface is public.
117        let mut info = std::mem::MaybeUninit::<libc::Dl_info>::uninit();
118        unsafe {
119            if libc::dladdr(*func.deref() as *const _, info.as_mut_ptr()) != 0 {
120                if std::ffi::CStr::from_ptr(info.assume_init().dli_fname).to_str().unwrap()
121                    != _lib_path.to_str().unwrap()
122                {
123                    return None;
124                }
125            }
126        }
127        // Return a pointer to the function.
128        Some(CodePtr(*func.deref() as *mut _))
129    }
130}
131
132impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
133pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
134    /// Call the native host function, with supplied arguments.
135    /// Needs to convert all the arguments from their Miri representations to
136    /// a native form (through `libffi` call).
137    /// Then, convert the return value from the native form into something that
138    /// can be stored in Miri's internal memory.
139    fn call_native_fn(
140        &mut self,
141        link_name: Symbol,
142        dest: &MPlaceTy<'tcx>,
143        args: &[OpTy<'tcx>],
144    ) -> InterpResult<'tcx, bool> {
145        let this = self.eval_context_mut();
146        // Get the pointer to the function in the shared object file if it exists.
147        let code_ptr = match this.get_func_ptr_explicitly_from_lib(link_name) {
148            Some(ptr) => ptr,
149            None => {
150                // Shared object file does not export this function -- try the shims next.
151                return interp_ok(false);
152            }
153        };
154
155        // Get the function arguments, and convert them to `libffi`-compatible form.
156        let mut libffi_args = Vec::<CArg>::with_capacity(args.len());
157        for arg in args.iter() {
158            if !matches!(arg.layout.backend_repr, BackendRepr::Scalar(_)) {
159                throw_unsup_format!("only scalar argument types are support for native calls")
160            }
161            let imm = this.read_immediate(arg)?;
162            libffi_args.push(imm_to_carg(&imm, this)?);
163            // If we are passing a pointer, prepare the memory it points to.
164            if matches!(arg.layout.ty.kind(), ty::RawPtr(..)) {
165                let ptr = imm.to_scalar().to_pointer(this)?;
166                let Some(prov) = ptr.provenance else {
167                    // Pointer without provenance may not access any memory.
168                    continue;
169                };
170                // We use `get_alloc_id` for its best-effort behaviour with Wildcard provenance.
171                let Some(alloc_id) = prov.get_alloc_id() else {
172                    // Wildcard pointer, whatever it points to must be already exposed.
173                    continue;
174                };
175                // The first time this happens, print a warning.
176                if !this.machine.native_call_mem_warned.replace(true) {
177                    // Newly set, so first time we get here.
178                    this.emit_diagnostic(NonHaltingDiagnostic::NativeCallSharedMem);
179                }
180
181                this.prepare_for_native_call(alloc_id, prov)?;
182            }
183        }
184
185        // FIXME: In the future, we should also call `prepare_for_native_call` on all previously
186        // exposed allocations, since C may access any of them.
187
188        // Convert them to `libffi::high::Arg` type.
189        let libffi_args = libffi_args
190            .iter()
191            .map(|arg| arg.arg_downcast())
192            .collect::<Vec<libffi::high::Arg<'_>>>();
193
194        // Call the function and store output, depending on return type in the function signature.
195        let ret = this.call_native_with_args(link_name, dest, code_ptr, libffi_args)?;
196        this.write_immediate(*ret, dest)?;
197        interp_ok(true)
198    }
199}
200
201#[derive(Debug, Clone)]
202/// Enum of supported arguments to external C functions.
203// We introduce this enum instead of just calling `ffi::arg` and storing a list
204// of `libffi::high::Arg` directly, because the `libffi::high::Arg` just wraps a reference
205// to the value it represents: https://docs.rs/libffi/latest/libffi/high/call/struct.Arg.html
206// and we need to store a copy of the value, and pass a reference to this copy to C instead.
207enum CArg {
208    /// 8-bit signed integer.
209    Int8(i8),
210    /// 16-bit signed integer.
211    Int16(i16),
212    /// 32-bit signed integer.
213    Int32(i32),
214    /// 64-bit signed integer.
215    Int64(i64),
216    /// isize.
217    ISize(isize),
218    /// 8-bit unsigned integer.
219    UInt8(u8),
220    /// 16-bit unsigned integer.
221    UInt16(u16),
222    /// 32-bit unsigned integer.
223    UInt32(u32),
224    /// 64-bit unsigned integer.
225    UInt64(u64),
226    /// usize.
227    USize(usize),
228    /// Raw pointer, stored as C's `void*`.
229    RawPtr(*mut std::ffi::c_void),
230}
231
232impl<'a> CArg {
233    /// Convert a `CArg` to a `libffi` argument type.
234    fn arg_downcast(&'a self) -> libffi::high::Arg<'a> {
235        match self {
236            CArg::Int8(i) => ffi::arg(i),
237            CArg::Int16(i) => ffi::arg(i),
238            CArg::Int32(i) => ffi::arg(i),
239            CArg::Int64(i) => ffi::arg(i),
240            CArg::ISize(i) => ffi::arg(i),
241            CArg::UInt8(i) => ffi::arg(i),
242            CArg::UInt16(i) => ffi::arg(i),
243            CArg::UInt32(i) => ffi::arg(i),
244            CArg::UInt64(i) => ffi::arg(i),
245            CArg::USize(i) => ffi::arg(i),
246            CArg::RawPtr(i) => ffi::arg(i),
247        }
248    }
249}
250
251/// Extract the scalar value from the result of reading a scalar from the machine,
252/// and convert it to a `CArg`.
253fn imm_to_carg<'tcx>(v: &ImmTy<'tcx>, cx: &impl HasDataLayout) -> InterpResult<'tcx, CArg> {
254    interp_ok(match v.layout.ty.kind() {
255        // If the primitive provided can be converted to a type matching the type pattern
256        // then create a `CArg` of this primitive value with the corresponding `CArg` constructor.
257        // the ints
258        ty::Int(IntTy::I8) => CArg::Int8(v.to_scalar().to_i8()?),
259        ty::Int(IntTy::I16) => CArg::Int16(v.to_scalar().to_i16()?),
260        ty::Int(IntTy::I32) => CArg::Int32(v.to_scalar().to_i32()?),
261        ty::Int(IntTy::I64) => CArg::Int64(v.to_scalar().to_i64()?),
262        ty::Int(IntTy::Isize) =>
263            CArg::ISize(v.to_scalar().to_target_isize(cx)?.try_into().unwrap()),
264        // the uints
265        ty::Uint(UintTy::U8) => CArg::UInt8(v.to_scalar().to_u8()?),
266        ty::Uint(UintTy::U16) => CArg::UInt16(v.to_scalar().to_u16()?),
267        ty::Uint(UintTy::U32) => CArg::UInt32(v.to_scalar().to_u32()?),
268        ty::Uint(UintTy::U64) => CArg::UInt64(v.to_scalar().to_u64()?),
269        ty::Uint(UintTy::Usize) =>
270            CArg::USize(v.to_scalar().to_target_usize(cx)?.try_into().unwrap()),
271        ty::RawPtr(..) => {
272            let s = v.to_scalar().to_pointer(cx)?.addr();
273            // This relies on the `expose_provenance` in `addr_from_alloc_id`.
274            CArg::RawPtr(std::ptr::with_exposed_provenance_mut(s.bytes_usize()))
275        }
276        _ => throw_unsup_format!("unsupported argument type for native call: {}", v.layout.ty),
277    })
278}
miri/shims/native_lib.rs

miri/shims/
native_lib.rs
