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Auto merge of #43217 - pnkfelix:alloc-requires-align-it-in-u32, r=alexcrichton

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Add precondition to `Layout` that the `align` fit in a u32.

Add precondition to `Layout` that the `align` not exceed 2^31.

This precondition takes the form of a behavorial change in `Layout::from_size_align` (so it returns `None` if the input `align` is too large) and a new requirement for safe usage of `Layout::from_size_align_unchecked`.

Fix #30170.
This commit is contained in:
bors 2017-07-28 00:49:39 +00:00
commit 63b3a03dc8
1 changed files with 15 additions and 7 deletions
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22
src/liballoc/allocator.rs
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@ -65,11 +65,13 @@ pub struct Layout {
impl Layout {
/// Constructs a `Layout` from a given `size` and `align`,
/// or returns `None` if either of the following conditions
/// or returns `None` if any of the following conditions
/// are not met:
///
/// * `align` must be a power of two,
///
/// * `align` must not exceed 2^31 (i.e. `1 << 31`),
///
/// * `size`, when rounded up to the nearest multiple of `align`,
/// must not overflow (i.e. the rounded value must be less than
/// `usize::MAX`).
@ -79,6 +81,10 @@ impl Layout {
return None;
}
if align > (1 << 31) {
return None;
}
// (power-of-two implies align != 0.)
// Rounded up size is:
@ -106,8 +112,10 @@ impl Layout {
///
/// # Unsafety
///
/// This function is unsafe as it does not verify that `align` is a power of
/// two nor that `size` aligned to `align` fits within the address space.
/// This function is unsafe as it does not verify that `align` is
/// a power-of-two that is also less than or equal to 2^31, nor
/// that `size` aligned to `align` fits within the address space
/// (i.e. the `Layout::from_size_align` preconditions).
#[inline]
pub unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Layout {
Layout { size: size, align: align }
@ -217,10 +225,10 @@ impl Layout {
Some(alloc_size) => alloc_size,
};
// We can assume that `self.align` is a power-of-two.
// Furthermore, `alloc_size` has alreayd been rounded up
// to a multiple of `self.align`; therefore, the call
// to `Layout::from_size_align` below should never panic.
// We can assume that `self.align` is a power-of-two that does
// not exceed 2^31. Furthermore, `alloc_size` has already been
// rounded up to a multiple of `self.align`; therefore, the
// call to `Layout::from_size_align` below should never panic.
Some((Layout::from_size_align(alloc_size, self.align).unwrap(), padded_size))
}