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Move a bunch of utility functionality into the newly introduced util module. In so doing we make CI test everything in this module under Miri. Signed-off-by: Daniel Müller <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,131 @@ | ||
| use std::borrow::Cow; | ||
| use std::mem::align_of; | ||
| use std::ptr::NonNull; | ||
| use std::slice; | ||
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| /// Check whether the given piece of memory is zeroed out. | ||
| /// | ||
| /// # Safety | ||
| /// The caller needs to make sure that `mem` points to `len` (or more) bytes of | ||
| /// valid memory. | ||
| pub(crate) unsafe fn is_mem_zero(mut mem: *const u8, mut len: usize) -> bool { | ||
| while len > 0 { | ||
| if unsafe { mem.read() } != 0 { | ||
| return false | ||
| } | ||
| mem = unsafe { mem.add(1) }; | ||
| len -= 1; | ||
| } | ||
| true | ||
| } | ||
|
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| /// "Safely" create a slice from an aligned user provided array. | ||
| pub(crate) unsafe fn slice_from_aligned_user_array<'t, T>( | ||
| items: *const T, | ||
| num_items: usize, | ||
| ) -> &'t [T] { | ||
| let items = if items.is_null() { | ||
| // `slice::from_raw_parts` requires a properly aligned non-NULL pointer. | ||
| // Craft one. | ||
| NonNull::dangling().as_ptr() | ||
| } else { | ||
| items | ||
| }; | ||
| unsafe { slice::from_raw_parts(items, num_items) } | ||
| } | ||
|
|
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| /// "Safely" create a slice from a user provided array. | ||
| pub(crate) unsafe fn slice_from_user_array<'t, T>(items: *const T, num_items: usize) -> Cow<'t, [T]> | ||
| where | ||
| T: Clone, | ||
| { | ||
| #[cold] | ||
| fn safely_copy_to_allocated_slow<T>(items: *const T, num_items: usize) -> Vec<T> | ||
| where | ||
| T: Clone, | ||
| { | ||
| if items.is_null() { | ||
| Vec::new() | ||
| } else { | ||
| let mut src = items; | ||
| let mut buffer = Vec::<T>::with_capacity(num_items); | ||
| let mut dst = buffer.as_mut_ptr(); | ||
|
|
||
| for _ in 0..num_items { | ||
| let () = unsafe { dst.write(src.read_unaligned()) }; | ||
| src = unsafe { src.add(1) }; | ||
| dst = unsafe { dst.add(1) }; | ||
| } | ||
| let () = unsafe { buffer.set_len(num_items) }; | ||
| buffer | ||
| } | ||
| } | ||
|
|
||
| if items.align_offset(align_of::<T>()) == 0 { | ||
| let slice = unsafe { slice_from_aligned_user_array(items, num_items) }; | ||
| Cow::Borrowed(slice) | ||
| } else { | ||
| let vec = safely_copy_to_allocated_slow(items, num_items); | ||
| Cow::Owned(vec) | ||
| } | ||
| } | ||
|
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| #[cfg(test)] | ||
| mod tests { | ||
| use super::*; | ||
|
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| use std::ops::Deref as _; | ||
| use std::ptr; | ||
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| /// Check that `is_mem_zero` works as it should. | ||
| #[test] | ||
| fn mem_zeroed_checking() { | ||
| let mut bytes = [0u8; 64]; | ||
| let zero = unsafe { is_mem_zero(bytes.as_slice().as_ptr(), bytes.len()) }; | ||
| assert!(zero, "{bytes:#x?}"); | ||
|
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| bytes[bytes.len() / 2] = 42; | ||
| let zero = unsafe { is_mem_zero(bytes.as_slice().as_ptr(), bytes.len()) }; | ||
| assert!(!zero, "{bytes:#x?}"); | ||
| } | ||
|
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| /// Test the `slice_from_aligned_user_array` helper in the presence of | ||
| /// various inputs. | ||
| #[test] | ||
| fn slice_creation() { | ||
| let slice = unsafe { slice_from_aligned_user_array::<u64>(ptr::null(), 0) }; | ||
| assert_eq!(slice, &[]); | ||
|
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| let array = []; | ||
| let slice = | ||
| unsafe { slice_from_aligned_user_array::<u64>(&array as *const _, array.len()) }; | ||
| assert_eq!(slice, &[]); | ||
|
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| let array = [42u64, 1337]; | ||
| let slice = | ||
| unsafe { slice_from_aligned_user_array::<u64>(&array as *const _, array.len()) }; | ||
| assert_eq!(slice, &[42, 1337]); | ||
| } | ||
|
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| /// Make sure that we can create a slice from a potentially unaligned C | ||
| /// array of values. | ||
| #[test] | ||
| fn unaligned_slice_creation() { | ||
| let slice = unsafe { slice_from_user_array(ptr::null::<u64>(), 0) }; | ||
| assert_eq!(slice.deref(), &[]); | ||
|
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| let mut buffer = [0u64; 8]; | ||
| let ptr = unsafe { buffer.as_mut_ptr().byte_add(3) }; | ||
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| let slice = unsafe { slice_from_user_array(ptr, buffer.len() - 1) }; | ||
| assert!(matches!(slice, Cow::Owned(..)), "{slice:?}"); | ||
| assert_eq!(slice.len(), buffer.len() - 1); | ||
|
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| let slice = unsafe { slice_from_user_array(buffer.as_ptr(), buffer.len()) }; | ||
| assert!(matches!(slice, Cow::Borrowed(..)), "{slice:?}"); | ||
| assert_eq!(slice.len(), buffer.len()); | ||
| } | ||
| } |