1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
#![stable(feature = "", since = "1.30.0")]
#![allow(non_camel_case_types)]

//! Utilities related to foreign function interface (FFI) bindings.

use crate::fmt;
use crate::marker::PhantomData;
use crate::ops::{Deref, DerefMut};

/// Equivalent to C's `void` type when used as a [pointer].
///
/// In essence, `*const c_void` is equivalent to C's `const void*`
/// and `*mut c_void` is equivalent to C's `void*`. That said, this is
/// *not* the same as C's `void` return type, which is Rust's `()` type.
///
/// To model pointers to opaque types in FFI, until `extern type` is
/// stabilized, it is recommended to use a newtype wrapper around an empty
/// byte array. See the [Nomicon] for details.
///
/// One could use `std::os::raw::c_void` if they want to support old Rust
/// compiler down to 1.1.0. After Rust 1.30.0, it was re-exported by
/// this definition. For more information, please read [RFC 2521].
///
/// [Nomicon]: https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs
/// [RFC 2521]: https://github.com/rust-lang/rfcs/blob/master/text/2521-c_void-reunification.md
// N.B., for LLVM to recognize the void pointer type and by extension
//     functions like malloc(), we need to have it represented as i8* in
//     LLVM bitcode. The enum used here ensures this and prevents misuse
//     of the "raw" type by only having private variants. We need two
//     variants, because the compiler complains about the repr attribute
//     otherwise and we need at least one variant as otherwise the enum
//     would be uninhabited and at least dereferencing such pointers would
//     be UB.
#[repr(u8)]
#[stable(feature = "core_c_void", since = "1.30.0")]
pub enum c_void {
    #[unstable(
        feature = "c_void_variant",
        reason = "temporary implementation detail",
        issue = "none"
    )]
    #[doc(hidden)]
    __variant1,
    #[unstable(
        feature = "c_void_variant",
        reason = "temporary implementation detail",
        issue = "none"
    )]
    #[doc(hidden)]
    __variant2,
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for c_void {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("c_void").finish()
    }
}

/// Basic implementation of a `va_list`.
// The name is WIP, using `VaListImpl` for now.
#[cfg(any(
    all(not(target_arch = "aarch64"), not(target_arch = "powerpc"), not(target_arch = "x86_64")),
    all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
    target_arch = "wasm32",
    target_arch = "asmjs",
    windows
))]
#[repr(transparent)]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
#[lang = "va_list"]
pub struct VaListImpl<'f> {
    ptr: *mut c_void,

    // Invariant over `'f`, so each `VaListImpl<'f>` object is tied to
    // the region of the function it's defined in
    _marker: PhantomData<&'f mut &'f c_void>,
}

#[cfg(any(
    all(not(target_arch = "aarch64"), not(target_arch = "powerpc"), not(target_arch = "x86_64")),
    all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
    target_arch = "wasm32",
    target_arch = "asmjs",
    windows
))]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'f> fmt::Debug for VaListImpl<'f> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "va_list* {:p}", self.ptr)
    }
}

/// AArch64 ABI implementation of a `va_list`. See the
/// [AArch64 Procedure Call Standard] for more details.
///
/// [AArch64 Procedure Call Standard]:
/// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf
#[cfg(all(
    target_arch = "aarch64",
    not(any(target_os = "macos", target_os = "ios")),
    not(windows)
))]
#[repr(C)]
#[derive(Debug)]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
#[lang = "va_list"]
pub struct VaListImpl<'f> {
    stack: *mut c_void,
    gr_top: *mut c_void,
    vr_top: *mut c_void,
    gr_offs: i32,
    vr_offs: i32,
    _marker: PhantomData<&'f mut &'f c_void>,
}

/// PowerPC ABI implementation of a `va_list`.
#[cfg(all(target_arch = "powerpc", not(windows)))]
#[repr(C)]
#[derive(Debug)]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
#[lang = "va_list"]
pub struct VaListImpl<'f> {
    gpr: u8,
    fpr: u8,
    reserved: u16,
    overflow_arg_area: *mut c_void,
    reg_save_area: *mut c_void,
    _marker: PhantomData<&'f mut &'f c_void>,
}

/// x86_64 ABI implementation of a `va_list`.
#[cfg(all(target_arch = "x86_64", not(windows)))]
#[repr(C)]
#[derive(Debug)]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
#[lang = "va_list"]
pub struct VaListImpl<'f> {
    gp_offset: i32,
    fp_offset: i32,
    overflow_arg_area: *mut c_void,
    reg_save_area: *mut c_void,
    _marker: PhantomData<&'f mut &'f c_void>,
}

/// A wrapper for a `va_list`
#[repr(transparent)]
#[derive(Debug)]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
pub struct VaList<'a, 'f: 'a> {
    #[cfg(any(
        all(
            not(target_arch = "aarch64"),
            not(target_arch = "powerpc"),
            not(target_arch = "x86_64")
        ),
        all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
        target_arch = "wasm32",
        target_arch = "asmjs",
        windows
    ))]
    inner: VaListImpl<'f>,

    #[cfg(all(
        any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
        any(not(target_arch = "aarch64"), not(any(target_os = "macos", target_os = "ios"))),
        not(target_arch = "wasm32"),
        not(target_arch = "asmjs"),
        not(windows)
    ))]
    inner: &'a mut VaListImpl<'f>,

    _marker: PhantomData<&'a mut VaListImpl<'f>>,
}

#[cfg(any(
    all(not(target_arch = "aarch64"), not(target_arch = "powerpc"), not(target_arch = "x86_64")),
    all(target_arch = "aarch64", any(target_os = "macos", target_os = "ios")),
    target_arch = "wasm32",
    target_arch = "asmjs",
    windows
))]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'f> VaListImpl<'f> {
    /// Convert a `VaListImpl` into a `VaList` that is binary-compatible with C's `va_list`.
    #[inline]
    pub fn as_va_list<'a>(&'a mut self) -> VaList<'a, 'f> {
        VaList { inner: VaListImpl { ..*self }, _marker: PhantomData }
    }
}

#[cfg(all(
    any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
    any(not(target_arch = "aarch64"), not(any(target_os = "macos", target_os = "ios"))),
    not(target_arch = "wasm32"),
    not(target_arch = "asmjs"),
    not(windows)
))]
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'f> VaListImpl<'f> {
    /// Convert a `VaListImpl` into a `VaList` that is binary-compatible with C's `va_list`.
    #[inline]
    pub fn as_va_list<'a>(&'a mut self) -> VaList<'a, 'f> {
        VaList { inner: self, _marker: PhantomData }
    }
}

#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'a, 'f: 'a> Deref for VaList<'a, 'f> {
    type Target = VaListImpl<'f>;

    #[inline]
    fn deref(&self) -> &VaListImpl<'f> {
        &self.inner
    }
}

#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'a, 'f: 'a> DerefMut for VaList<'a, 'f> {
    #[inline]
    fn deref_mut(&mut self) -> &mut VaListImpl<'f> {
        &mut self.inner
    }
}

// The VaArgSafe trait needs to be used in public interfaces, however, the trait
// itself must not be allowed to be used outside this module. Allowing users to
// implement the trait for a new type (thereby allowing the va_arg intrinsic to
// be used on a new type) is likely to cause undefined behavior.
//
// FIXME(dlrobertson): In order to use the VaArgSafe trait in a public interface
// but also ensure it cannot be used elsewhere, the trait needs to be public
// within a private module. Once RFC 2145 has been implemented look into
// improving this.
mod sealed_trait {
    /// Trait which permits the allowed types to be used with [super::VaListImpl::arg].
    #[unstable(
        feature = "c_variadic",
        reason = "the `c_variadic` feature has not been properly tested on \
                  all supported platforms",
        issue = "44930"
    )]
    pub trait VaArgSafe {}
}

macro_rules! impl_va_arg_safe {
    ($($t:ty),+) => {
        $(
            #[unstable(feature = "c_variadic",
                       reason = "the `c_variadic` feature has not been properly tested on \
                                 all supported platforms",
                       issue = "44930")]
            impl sealed_trait::VaArgSafe for $t {}
        )+
    }
}

impl_va_arg_safe! {i8, i16, i32, i64, usize}
impl_va_arg_safe! {u8, u16, u32, u64, isize}
impl_va_arg_safe! {f64}

#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<T> sealed_trait::VaArgSafe for *mut T {}
#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<T> sealed_trait::VaArgSafe for *const T {}

#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'f> VaListImpl<'f> {
    /// Advance to the next arg.
    #[inline]
    pub unsafe fn arg<T: sealed_trait::VaArgSafe>(&mut self) -> T {
        // SAFETY: the caller must uphold the safety contract for `va_arg`.
        unsafe { va_arg(self) }
    }

    /// Copies the `va_list` at the current location.
    pub unsafe fn with_copy<F, R>(&self, f: F) -> R
    where
        F: for<'copy> FnOnce(VaList<'copy, 'f>) -> R,
    {
        let mut ap = self.clone();
        let ret = f(ap.as_va_list());
        // SAFETY: the caller must uphold the safety contract for `va_end`.
        unsafe {
            va_end(&mut ap);
        }
        ret
    }
}

#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'f> Clone for VaListImpl<'f> {
    #[inline]
    fn clone(&self) -> Self {
        let mut dest = crate::mem::MaybeUninit::uninit();
        // SAFETY: we write to the `MaybeUninit`, thus it is initialized and `assume_init` is legal
        unsafe {
            va_copy(dest.as_mut_ptr(), self);
            dest.assume_init()
        }
    }
}

#[unstable(
    feature = "c_variadic",
    reason = "the `c_variadic` feature has not been properly tested on \
              all supported platforms",
    issue = "44930"
)]
impl<'f> Drop for VaListImpl<'f> {
    fn drop(&mut self) {
        // FIXME: this should call `va_end`, but there's no clean way to
        // guarantee that `drop` always gets inlined into its caller,
        // so the `va_end` would get directly called from the same function as
        // the corresponding `va_copy`. `man va_end` states that C requires this,
        // and LLVM basically follows the C semantics, so we need to make sure
        // that `va_end` is always called from the same function as `va_copy`.
        // For more details, see https://github.com/rust-lang/rust/pull/59625
        // and https://llvm.org/docs/LangRef.html#llvm-va-end-intrinsic.
        //
        // This works for now, since `va_end` is a no-op on all current LLVM targets.
    }
}

extern "rust-intrinsic" {
    /// Destroy the arglist `ap` after initialization with `va_start` or
    /// `va_copy`.
    fn va_end(ap: &mut VaListImpl<'_>);

    /// Copies the current location of arglist `src` to the arglist `dst`.
    fn va_copy<'f>(dest: *mut VaListImpl<'f>, src: &VaListImpl<'f>);

    /// Loads an argument of type `T` from the `va_list` `ap` and increment the
    /// argument `ap` points to.
    fn va_arg<T: sealed_trait::VaArgSafe>(ap: &mut VaListImpl<'_>) -> T;
}