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    #![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].
    ///
    /// [pointer]: ../../std/primitive.pointer.html
    /// [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.pad("c_void")
        }
    }

    /// 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", 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", 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(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", 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(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", 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(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 [VaList::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;
    }