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differentiate between layout and alloc_layout

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Strophox 2024-05-23 16:00:23 +02:00
parent 56c363b43e
commit 1b374dfd9b
1 changed files with 18 additions and 10 deletions
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28
src/tools/miri/src/alloc_bytes.rs
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@ -13,7 +13,10 @@ pub struct MiriAllocBytes {
/// Stored layout information about the allocation.
layout: alloc::Layout,
/// Pointer to the allocation contents.
/// Invariant: `self.ptr` points to memory allocated with `self.layout`.
/// Invariant:
/// * If `self.layout.size() == 0`, then `self.ptr` is some suitably aligned pointer
/// that was allocated with the same layout but `size == 1`.
/// * Otherwise, `self.ptr` points to memory allocated with `self.layout`.
ptr: *mut u8,
}
@ -27,8 +30,13 @@ impl Clone for MiriAllocBytes {
impl Drop for MiriAllocBytes {
fn drop(&mut self) {
let alloc_layout = if self.layout.size() == 0 {
Layout::from_size_align(1, self.layout.align()).unwrap()
} else {
self.layout
};
// SAFETY: Invariant, `self.ptr` points to memory allocated with `self.layout`.
unsafe { alloc::dealloc(self.ptr, self.layout) }
unsafe { alloc::dealloc(self.ptr, alloc_layout) }
}
}
@ -51,21 +59,21 @@ impl std::ops::DerefMut for MiriAllocBytes {
}
impl MiriAllocBytes {
/// This method factors out how a `MiriAllocBytes` object is allocated,
/// specifically given an allocation function `alloc_fn`.
/// `alloc_fn` is only used with `size != 0`.
/// Returns `Err(layout)` if the allocation function returns a `ptr` where `ptr.is_null()`.
/// This method factors out how a `MiriAllocBytes` object is allocated, given a specific allocation function.
/// If `size == 0` we allocate using a different `alloc_layout` with `size = 1`, to ensure each allocation has a unique address.
/// Returns `Err(alloc_layout)` if the allocation function returns a `ptr` where `ptr.is_null()`.
fn alloc_with(
size: usize,
align: usize,
alloc_fn: impl FnOnce(Layout) -> *mut u8,
) -> Result<MiriAllocBytes, Layout> {
// When size is 0 we allocate 1 byte anyway, so addresses don't possibly overlap.
let size = if size == 0 { 1 } else { size };
let layout = Layout::from_size_align(size, align).unwrap();
let ptr = alloc_fn(layout);
// When size is 0 we allocate 1 byte anyway, to ensure each allocation has a unique address.
let alloc_layout =
if size == 0 { Layout::from_size_align(1, align).unwrap() } else { layout };
let ptr = alloc_fn(alloc_layout);
if ptr.is_null() {
Err(layout)
Err(alloc_layout)
} else {
// SAFETY: All `MiriAllocBytes` invariants are fulfilled.
Ok(Self { ptr, layout })