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Fix tests
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@ubsan
ubsan committed Jul 5, 2016
1 parent 9e94ebf commit 7ec44e6
Showing 1 changed file with 138 additions and 100 deletions.
238 changes: 138 additions & 100 deletions src/libcore/intrinsics.rs
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Expand Up @@ -286,12 +286,13 @@ extern "rust-intrinsic" {
/// `transmute::<T, U>(t)` is semantically equivalent to the following:
///
/// ```
/// use std::{mem, ptr};
/// // assuming that T and U are the same size
/// unsafe fn transmute<T, U>(t: T) -> U {
/// let u: U = mem::uninitialized();
/// std::ptr::copy_nonoverlapping(&t as *const T as *const u8,
/// &mut u as *mut U as *mut u8,
/// mem::size_of::<T>());
/// let mut u: U = mem::uninitialized();
/// ptr::copy_nonoverlapping(&t as *const T as *const u8,
/// &mut u as *mut U as *mut u8,
/// mem::size_of::<T>());
/// mem::forget(t);
/// u
/// }
Expand All @@ -310,88 +311,115 @@ extern "rust-intrinsic" {
/// through other means. Some more or less common uses, and a better way,
/// are as follows:
///
/// Turning a pointer into a `usize`:
/// ```
/// let ptr = &0;
/// let ptr_num_transmute = mem::transmute::<&i32, usize>(ptr);
/// // Use `as` casts instead
/// let ptr_num_cast = ptr as *const i32 as usize;
/// ```
/// use std::mem;
///
/// // turning a pointer into a usize
/// {
/// let ptr = &0;
/// let ptr_num_transmute = mem::transmute::<&i32, usize>(ptr);
/// // Use `as` casts instead
/// let ptr_num_cast = ptr as *const i32 as usize;
/// }
///
/// // Turning a *mut T into an &mut T
/// {
/// let ptr: *mut i32 = &mut 0;
/// let ref_transmuted = mem::transmute::<*mut i32, &mut i32>(ptr);
/// // Use reborrows
/// let ref_casted = &mut *ptr;
/// }
///
/// // Turning an &mut T into an &mut U
/// {
/// let ptr = &mut 0;
/// let val_transmuted = mem::transmute::<&mut i32, &mut u32>(ptr);
/// // Now let's put together `as` and reborrowing
/// let val_casts = &mut *(ptr as *mut i32 as *mut u32);
/// }
/// Turning a `*mut T` into an `&mut T`:
/// ```
/// let ptr: *mut i32 = &mut 0;
/// let ref_transmuted = mem::transmute::<*mut i32, &mut i32>(ptr);
/// // Use reborrows
/// let ref_casted = &mut *ptr;
/// ```
///
/// // Turning an `&str` into an `&[u8]`
/// {
/// // this is not a good way to do this.
/// let slice = unsafe { mem::transmute::<&str, &[u8]>("Rust") };
/// assert_eq!(slice, [82, 117, 115, 116]);
/// // You could use `str::as_bytes`
/// let slice = "Rust".as_bytes();
/// assert_eq!(slice, [82, 117, 115, 116]);
/// // Or, just use a byte string, if you have control over the string
/// // literal
/// assert_eq!(b"Rust", [82, 117, 116, 116]);
/// }
/// Turning an `&mut T` into an `&mut U`:
/// ```
/// let ptr = &mut 0;
/// let val_transmuted = mem::transmute::<&mut i32, &mut u32>(ptr);
/// // Now let's put together `as` and reborrowing
/// let val_casts = &mut *(ptr as *mut i32 as *mut u32);
/// ```
///
/// // Turning a Vec<&T> into a Vec<Option<&T>>
/// {
/// let store = [0, 1, 2, 3];
/// let v_orig = store.iter().collect::<Vec<&i32>>();
/// // Using transmute; Undefined Behavior
/// let v_transmuted = mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(
/// v_orig.clone());
/// // The suggested, safe way
/// let v_collected = v_orig.clone()
/// .into_iter()
/// .map(|r| Some(r))
/// .collect::<Vec<Option<&i32>>>();
/// // The no-copy, unsafe way, still using transmute, but not UB
/// // This is equivalent to the original, but safer, and reuses the
/// // same Vec internals. Therefore the new inner type must have the
/// // exact same size, and the same or lesser alignment, as the old
/// // type. The same caveats exist for this method as transmute, for
/// // the original inner type (`&i32`) to the converted inner type
/// // (`Option<&i32>`), so read the nomicon page linked above.
/// let v_no_copy = Vec::from_raw_parts(v_orig.as_mut_ptr(),
/// v_orig.len(),
/// v_orig.capacity());
/// mem::forget(v_orig);
/// }
/// Turning an `&str` into an `&[u8]`:
/// ```
/// // this is not a good way to do this.
/// let slice = unsafe { mem::transmute::<&str, &[u8]>("Rust") };
/// assert_eq!(slice, [82, 117, 115, 116]);
/// // You could use `str::as_bytes`
/// let slice = "Rust".as_bytes();
/// assert_eq!(slice, [82, 117, 115, 116]);
/// // Or, just use a byte string, if you have control over the string
/// // literal
/// assert_eq!(b"Rust", [82, 117, 116, 116]);
/// ```
///
/// Turning a `Vec<&T>` into a `Vec<Option<&T>>`:
/// ```
/// let store = [0, 1, 2, 3];
/// let v_orig = store.iter().collect::<Vec<&i32>>();
/// // Using transmute: this is Undefined Behavior, and a bad idea
/// // However, it is no-copy
/// let v_transmuted = mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(
/// v_orig.clone());
/// // This is the suggested, safe way
/// // It does copy the entire Vector, though, into a new array
/// let v_collected = v_orig.clone()
/// .into_iter()
/// .map(|r| Some(r))
/// .collect::<Vec<Option<&i32>>>();
/// // The no-copy, unsafe way, still using transmute, but not UB
/// // This is equivalent to the original, but safer, and reuses the
/// // same Vec internals. Therefore the new inner type must have the
/// // exact same size, and the same or lesser alignment, as the old
/// // type. The same caveats exist for this method as transmute, for
/// // the original inner type (`&i32`) to the converted inner type
/// // (`Option<&i32>`), so read the nomicon page linked above.
/// let v_from_raw = Vec::from_raw_parts(v_orig.as_mut_ptr(),
/// v_orig.len(),
/// v_orig.capacity());
/// mem::forget(v_orig);
/// ```
///
/// // Copying an `&mut T` to reslice:
/// {
/// fn split_at_mut_transmute<T>(slice: &mut [T], index: usize)
/// -> (&mut [T], &mut [T]) {
/// let len = slice.len();
/// assert!(index < len);
/// Implemententing `split_at_mut`:
/// ```
/// use std::{slice, mem};
/// // There are multiple ways to do this; and there are multiple problems
/// // with the following, transmute, way
/// fn split_at_mut_transmute<T>(slice: &mut [T], index: usize)
/// -> (&mut [T], &mut [T]) {
/// let len = slice.len();
/// assert!(index < len);
/// unsafe {
/// let slice2 = mem::transmute::<&mut [T], &mut [T]>(slice);
/// (slice[0..index], slice2[index..len])
/// // first: transmute is not typesafe; all it checks is that T and
/// // U are of the same size. Second, right here, you have two
/// // mutable references pointing to the same memory
/// (&mut slice[0..index], &mut slice2[index..len])
/// }
/// // Again, use `as` and reborrowing
/// fn split_at_mut_casts<T>(slice: &mut [T], index: usize)
/// -> (&mut [T], &mut [T]) {
/// let len = slice.len();
/// assert!(index < len);
/// let slice2 = &mut *(slice as *mut [T]); // actually typesafe!
/// (slice[0..index], slice2[index..len])
/// }
/// // This gets rid of the typesafety problems; `&mut *` will *only* give
/// // you an &mut T from an &mut T or *mut T
/// fn split_at_mut_casts<T>(slice: &mut [T], index: usize)
/// -> (&mut [T], &mut [T]) {
/// let len = slice.len();
/// assert!(index < len);
/// unsafe {
/// let slice2 = &mut *(slice as *mut [T]);
/// // however, you still have two mutable references pointing to
/// // the same memory
/// (&mut slice[0..index], &mut slice2[index..len])
/// }
/// }
/// // This is how the standard library does it. This is the best method, if
/// // you need to do something like this
/// fn split_at_stdlib<T>(slice: &mut [T], index: usize)
/// -> (&mut [T], &mut [T]) {
/// let len = self.len();
/// let ptr = self.as_mut_ptr();
/// unsafe {
/// assert!(mid <= len);
/// // This now has three mutable references pointing at the same
/// // memory. `slice`, the rvalue ret.0, and the rvalue ret.1.
/// // However, `slice` is never used after `let ptr = ...`, and so
/// // one can treat it as "dead", and therefore, you only have two
/// // real mutable slices.
/// (slice::from_raw_parts_mut(ptr, mid),
/// slice::from_raw_parts_mut(ptr.offset(mid as isize), len - mid))
/// }
/// }
/// ```
Expand All @@ -400,39 +428,49 @@ extern "rust-intrinsic" {
///
/// There are valid uses of transmute, though they are few and far between.
///
/// Getting the bitpattern of a floating point type:
/// ```
/// let bitpattern = std::mem::transmute::<f32, u32>(1.0);
/// assert_eq!(bitpattern, 0x3F800000);
/// ```
/// // getting the bitpattern of a floating point type
/// {
/// let x = mem::transmute::<f32, u32>(0.0/0.0)
///
/// Turning a pointer into a function pointer (this isn't guaranteed to
/// work in Rust, although, for example, Linux does make this guarantee):
/// ```
/// fn foo() -> i32 {
/// 0
/// }
/// let pointer = foo as *const ();
/// let function = std::mem::transmute::<*const (), fn() -> i32>(pointer)
/// assert_eq!(function(), 0);
/// ```
///
/// Extending a lifetime, or shortening an invariant an invariant lifetime;
/// this is advanced, very unsafe rust:
/// ```
/// use std::mem;
///
/// // turning a pointer into a function pointer
/// {
/// // in file.c: `int foo(void) { ... }`
/// let handle: *mut libc::c_void = libc::dlopen(
/// b"file.so\0".as_ptr() as *const libc::c_char, libc::RTLD_LAZY);
/// let foo: *mut libc::c_void = libc::dlsym(
/// handle,
/// b"foo\0".as_ptr() as *const libc::c_char);
/// let foo = mem::transmute::<*mut libc::c_void,
/// extern fn() -> libc::c_int>(foo);
/// println!("{}", foo());
/// struct R<'a>(&'a i32);
/// unsafe fn extend_lifetime<'b>(r: R<'b>) -> R<'static> {
/// mem::transmute::<R<'b>, R<'static>>(ptr);
/// }
///
///
/// // extending an invariant lifetime; this is advanced, very unsafe rust
/// {
/// struct T<'a>(&'a i32);
/// let value = 0;
/// let t = T::new(&value);
/// let ptr = &mut t;
/// let ptr_extended = mem::transmute::<&mut T, &mut T<'static>>(ptr);
/// unsafe fn shorten_invariant<'b, 'c>(r: &'b mut R<'static>)
/// -> &'b R<'c> {
/// let ref_to_original =
/// mem::transmute::<&'b mut R<'static>, &'b mut R<'c>>(
/// ref_to_extended);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn transmute<T, U>(e: T) -> U;

/// Gives the address for the return value of the enclosing function.
///
/// Using this intrinsic in a function that does not use an out pointer
/// will trigger a compiler error.
pub fn return_address() -> *const u8;

/// Returns `true` if the actual type given as `T` requires drop
/// glue; returns `false` if the actual type provided for `T`
/// implements `Copy`.
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