src/libcore/ffi.rs

   1 #![stable(feature = "", since = "1.30.0")]
   2
   3 #![allow(non_camel_case_types)]
   4
   5 //! Utilities related to FFI bindings.
   6
   7 use ::fmt;
   8
   9 /// Equivalent to C's `void` type when used as a [pointer].
  10 ///
  11 /// In essence, `*const c_void` is equivalent to C's `const void*`
  12 /// and `*mut c_void` is equivalent to C's `void*`. That said, this is
  13 /// *not* the same as C's `void` return type, which is Rust's `()` type.
  14 ///
  15 /// To model pointers to opaque types in FFI, until `extern type` is
  16 /// stabilized, it is recommended to use a newtype wrapper around an empty
  17 /// byte array. See the [Nomicon] for details.
  18 ///
  19 /// [pointer]: ../../std/primitive.pointer.html
  20 /// [Nomicon]: https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs
  21 // N.B., for LLVM to recognize the void pointer type and by extension
  22 //     functions like malloc(), we need to have it represented as i8* in
  23 //     LLVM bitcode. The enum used here ensures this and prevents misuse
  24 //     of the "raw" type by only having private variants. We need two
  25 //     variants, because the compiler complains about the repr attribute
  26 //     otherwise and we need at least one variant as otherwise the enum
  27 //     would be uninhabited and at least dereferencing such pointers would
  28 //     be UB.
  29 #[repr(u8)]
  30 #[stable(feature = "raw_os", since = "1.1.0")]
  31 pub enum c_void {
  32     #[unstable(feature = "c_void_variant", reason = "temporary implementation detail",
  33                issue = "0")]
  34     #[doc(hidden)] __variant1,
  35     #[unstable(feature = "c_void_variant", reason = "temporary implementation detail",
  36                issue = "0")]
  37     #[doc(hidden)] __variant2,
  38 }
  39
  40 #[stable(feature = "std_debug", since = "1.16.0")]
  41 impl fmt::Debug for c_void {
  42     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  43         f.pad("c_void")
  44     }
  45 }
  46
  47 /// Basic implementation of a `va_list`.
  48 #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
  49               not(target_arch = "x86_64")),
  50           all(target_arch = "aarch4", target_os = "ios"),
  51           windows))]
  52 #[unstable(feature = "c_variadic",
  53            reason = "the `c_variadic` feature has not been properly tested on \
  54                      all supported platforms",
  55            issue = "44930")]
  56 extern {
  57     type VaListImpl;
  58 }
  59
  60 #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
  61               not(target_arch = "x86_64")),
  62           windows))]
  63 impl fmt::Debug for VaListImpl {
  64     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  65         write!(f, "va_list* {:p}", self)
  66     }
  67 }
  68
  69 /// AArch64 ABI implementation of a `va_list`. See the
  70 /// [Aarch64 Procedure Call Standard] for more details.
  71 ///
  72 /// [AArch64 Procedure Call Standard]:
  73 /// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf
  74 #[cfg(all(target_arch = "aarch64", not(windows)))]
  75 #[repr(C)]
  76 #[derive(Debug)]
  77 #[unstable(feature = "c_variadic",
  78            reason = "the `c_variadic` feature has not been properly tested on \
  79                      all supported platforms",
  80            issue = "44930")]
  81 struct VaListImpl {
  82     stack: *mut (),
  83     gr_top: *mut (),
  84     vr_top: *mut (),
  85     gr_offs: i32,
  86     vr_offs: i32,
  87 }
  88
  89 /// PowerPC ABI implementation of a `va_list`.
  90 #[cfg(all(target_arch = "powerpc", not(windows)))]
  91 #[repr(C)]
  92 #[derive(Debug)]
  93 #[unstable(feature = "c_variadic",
  94            reason = "the `c_variadic` feature has not been properly tested on \
  95                      all supported platforms",
  96            issue = "44930")]
  97 struct VaListImpl {
  98     gpr: u8,
  99     fpr: u8,
 100     reserved: u16,
 101     overflow_arg_area: *mut (),
 102     reg_save_area: *mut (),
 103 }
 104
 105 /// x86_64 ABI implementation of a `va_list`.
 106 #[cfg(all(target_arch = "x86_64", not(windows)))]
 107 #[repr(C)]
 108 #[derive(Debug)]
 109 #[unstable(feature = "c_variadic",
 110            reason = "the `c_variadic` feature has not been properly tested on \
 111                      all supported platforms",
 112            issue = "44930")]
 113 struct VaListImpl {
 114     gp_offset: i32,
 115     fp_offset: i32,
 116     overflow_arg_area: *mut (),
 117     reg_save_area: *mut (),
 118 }
 119
 120 /// A wrapper for a `va_list`
 121 #[lang = "va_list"]
 122 #[derive(Debug)]
 123 #[unstable(feature = "c_variadic",
 124            reason = "the `c_variadic` feature has not been properly tested on \
 125                      all supported platforms",
 126            issue = "44930")]
 127 #[repr(transparent)]
 128 pub struct VaList<'a>(&'a mut VaListImpl);
 129
 130 // The VaArgSafe trait needs to be used in public interfaces, however, the trait
 131 // itself must not be allowed to be used outside this module. Allowing users to
 132 // implement the trait for a new type (thereby allowing the va_arg intrinsic to
 133 // be used on a new type) is likely to cause undefined behavior.
 134 //
 135 // FIXME(dlrobertson): In order to use the VaArgSafe trait in a public interface
 136 // but also ensure it cannot be used elsewhere, the trait needs to be public
 137 // within a private module. Once RFC 2145 has been implemented look into
 138 // improving this.
 139 mod sealed_trait {
 140     /// Trait which whitelists the allowed types to be used with [VaList::arg]
 141     ///
 142     /// [VaList::va_arg]: struct.VaList.html#method.arg
 143     #[unstable(feature = "c_variadic",
 144                reason = "the `c_variadic` feature has not been properly tested on \
 145                          all supported platforms",
 146                issue = "44930")]
 147     pub trait VaArgSafe {}
 148 }
 149
 150 macro_rules! impl_va_arg_safe {
 151     ($($t:ty),+) => {
 152         $(
 153             #[unstable(feature = "c_variadic",
 154                        reason = "the `c_variadic` feature has not been properly tested on \
 155                                  all supported platforms",
 156                        issue = "44930")]
 157             impl sealed_trait::VaArgSafe for $t {}
 158         )+
 159     }
 160 }
 161
 162 impl_va_arg_safe!{i8, i16, i32, i64, usize}
 163 impl_va_arg_safe!{u8, u16, u32, u64, isize}
 164 impl_va_arg_safe!{f64}
 165
 166 #[unstable(feature = "c_variadic",
 167            reason = "the `c_variadic` feature has not been properly tested on \
 168                      all supported platforms",
 169            issue = "44930")]
 170 impl<T> sealed_trait::VaArgSafe for *mut T {}
 171 #[unstable(feature = "c_variadic",
 172            reason = "the `c_variadic` feature has not been properly tested on \
 173                      all supported platforms",
 174            issue = "44930")]
 175 impl<T> sealed_trait::VaArgSafe for *const T {}
 176
 177 impl<'a> VaList<'a> {
 178     /// Advance to the next arg.
 179     #[unstable(feature = "c_variadic",
 180                reason = "the `c_variadic` feature has not been properly tested on \
 181                          all supported platforms",
 182                issue = "44930")]
 183     pub unsafe fn arg<T: sealed_trait::VaArgSafe>(&mut self) -> T {
 184         va_arg(self)
 185     }
 186
 187     /// Copies the `va_list` at the current location.
 188     #[unstable(feature = "c_variadic",
 189                reason = "the `c_variadic` feature has not been properly tested on \
 190                          all supported platforms",
 191                issue = "44930")]
 192     pub unsafe fn copy<F, R>(&self, f: F) -> R
 193             where F: for<'copy> FnOnce(VaList<'copy>) -> R {
 194         #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
 195                       not(target_arch = "x86_64")),
 196                   all(target_arch = "aarch4", target_os = "ios"),
 197                   windows))]
 198         let mut ap = va_copy(self);
 199         #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
 200                   not(windows)))]
 201         let mut ap_inner = va_copy(self);
 202         #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
 203                   not(windows)))]
 204         let mut ap = VaList(&mut ap_inner);
 205         let ret = f(VaList(ap.0));
 206         va_end(&mut ap);
 207         ret
 208     }
 209 }
 210
 211 extern "rust-intrinsic" {
 212     /// Destroy the arglist `ap` after initialization with `va_start` or
 213     /// `va_copy`.
 214     fn va_end(ap: &mut VaList);
 215
 216     /// Copies the current location of arglist `src` to the arglist `dst`.
 217     #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
 218                   not(target_arch = "x86_64")),
 219               windows))]
 220     fn va_copy<'a>(src: &VaList<'a>) -> VaList<'a>;
 221     #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
 222               not(windows)))]
 223     fn va_copy(src: &VaList) -> VaListImpl;
 224
 225     /// Loads an argument of type `T` from the `va_list` `ap` and increment the
 226     /// argument `ap` points to.
 227     fn va_arg<T: sealed_trait::VaArgSafe>(ap: &mut VaList) -> T;
 228 }