openharmony/third_party_rust_memoffset
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avoid use of size_of_val in span_of

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This commit is contained in:
Ralf Jung 2021-03-27 15:21:43 +01:00
parent ca3425e81a
commit 5f9e008def
2 changed files with 28 additions and 24 deletions
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10
src/lib.rs
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@ -83,6 +83,16 @@ pub use core::mem;
#[doc(hidden)]
pub use core::ptr;
/// Hiden module to things the macros need to access.
#[doc(hidden)]
pub mod __priv {
/// Use type inference to obtain the size of the pointee (without actually using the pointer).
#[doc(hidden)]
pub fn size_of_pointee<T>(_ptr: *const T) -> usize {
core::mem::size_of::<T>()
}
}
#[macro_use]
mod raw_field;
#[macro_use]

42
src/span_of.rs
View File

@ -95,23 +95,21 @@ macro_rules! span_of {
};
// No explicit begin for range.
(@helper $root:ident, $parent:path, [] ..) => {{
// UB due to taking references to uninitialized fields for `size_of_val`.
($root as usize,
$root as usize + $crate::mem::size_of_val(&(*$root)))
$root as usize + $crate::__priv::size_of_pointee($root))
}};
(@helper $root:ident, $parent:path, [] ..= $field:tt) => {{
// UB due to taking references to uninitialized fields for `size_of_val`.
($root as usize,
raw_field!($root, $parent, $field) as usize + $crate::mem::size_of_val(&(*$root).$field))
(@helper $root:ident, $parent:path, [] ..= $end:tt) => {{
let end = raw_field!($root, $parent, $end);
($root as usize, end as usize + $crate::__priv::size_of_pointee(end))
}};
(@helper $root:ident, $parent:path, [] .. $field:tt) => {{
($root as usize, raw_field!($root, $parent, $field) as usize)
(@helper $root:ident, $parent:path, [] .. $end:tt) => {{
($root as usize, raw_field!($root, $parent, $end) as usize)
}};
// Explicit begin and end for range.
(@helper $root:ident, $parent:path, # $begin:tt [] ..= $end:tt) => {{
// UB due to taking references to uninitialized fields for `size_of_val`.
(raw_field!($root, $parent, $begin) as usize,
raw_field!($root, $parent, $end) as usize + $crate::mem::size_of_val(&(*$root).$end))
let begin = raw_field!($root, $parent, $begin);
let end = raw_field!($root, $parent, $end);
(begin as usize, end as usize + $crate::__priv::size_of_pointee(end))
}};
(@helper $root:ident, $parent:path, # $begin:tt [] .. $end:tt) => {{
(raw_field!($root, $parent, $begin) as usize,
@ -119,19 +117,17 @@ macro_rules! span_of {
}};
// No explicit end for range.
(@helper $root:ident, $parent:path, # $begin:tt [] ..) => {{
// UB due to taking references to uninitialized fields for `size_of_val`.
(raw_field!($root, $parent, $begin) as usize,
$root as usize + $crate::mem::size_of_val(&*$root))
$root as usize + $crate::__priv::size_of_pointee($root))
}};
(@helper $root:ident, $parent:path, # $begin:tt [] ..=) => {{
_memoffset__compile_error!(
"Found inclusive range to the end of a struct. Did you mean '..' instead of '..='?")
}};
// Just one field.
(@helper $root:ident, $parent:path, # $begin:tt []) => {{
// UB due to taking references to uninitialized fields for `size_of_val`.
(raw_field!($root, $parent, $begin) as usize,
raw_field!($root, $parent, $begin) as usize + $crate::mem::size_of_val(&(*$root).$begin))
(@helper $root:ident, $parent:path, # $field:tt []) => {{
let field = raw_field!($root, $parent, $field);
(field as usize, field as usize + $crate::__priv::size_of_pointee(field))
}};
// Parsing.
(@helper $root:ident, $parent:path, $(# $begin:tt)+ [] $tt:tt $($rest:tt)*) => {{
@ -143,13 +139,11 @@ macro_rules! span_of {
// Entry point.
($sty:path, $($exp:tt)+) => ({
unsafe {
// Get a base pointer.
_memoffset__let_base_ptr!(root, $sty);
let base = root as usize;
let (begin, end) = span_of!(@helper root, $sty, [] $($exp)*);
begin-base..end-base
}
// Get a base pointer.
_memoffset__let_base_ptr!(root, $sty);
let base = root as usize;
let (begin, end) = span_of!(@helper root, $sty, [] $($exp)*);
begin-base..end-base
});
}