A raw ref of a deref is always safe

This commit is contained in:
Michael Goulet 2024-08-17 13:03:27 -04:00
parent 1b3b8e7b02
commit f2a80a0f89
4 changed files with 18 additions and 11 deletions

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@ -512,17 +512,11 @@ fn visit_expr(&mut self, expr: &'a Expr<'tcx>) {
// THIR desugars UNSAFE_STATIC into *UNSAFE_STATIC_REF, where // THIR desugars UNSAFE_STATIC into *UNSAFE_STATIC_REF, where
// UNSAFE_STATIC_REF holds the addr of the UNSAFE_STATIC, so: take two steps // UNSAFE_STATIC_REF holds the addr of the UNSAFE_STATIC, so: take two steps
&& let ExprKind::Deref { arg } = self.thir[arg].kind && let ExprKind::Deref { arg } = self.thir[arg].kind
// FIXME(workingjubiee): we lack a clear reason to reject ThreadLocalRef here,
// but we also have no conclusive reason to allow it either!
&& let ExprKind::StaticRef { .. } = self.thir[arg].kind
{ {
// A raw ref to a place expr, even an "unsafe static", is okay! // Taking a raw ref to a deref place expr is always safe.
// We short-circuit to not recursively traverse this expression. // Make sure the expression we're deref'ing is safe, though.
visit::walk_expr(self, &self.thir[arg]);
return; return;
// note: const_mut_refs enables this code, and it currently remains unsafe:
// static mut BYTE: u8 = 0;
// static mut BYTE_PTR: *mut u8 = unsafe { addr_of_mut!(BYTE) };
// static mut DEREF_BYTE_PTR: *mut u8 = unsafe { addr_of_mut!(*BYTE_PTR) };
} }
} }
ExprKind::Deref { arg } => { ExprKind::Deref { arg } => {

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@ -9,7 +9,6 @@
// (it's fine to create raw refs to places!) the following derefs the ptr before creating its ref! // (it's fine to create raw refs to places!) the following derefs the ptr before creating its ref!
static mut DEREF_BYTE_PTR: *mut u8 = ptr::addr_of_mut!(*BYTE_PTR); static mut DEREF_BYTE_PTR: *mut u8 = ptr::addr_of_mut!(*BYTE_PTR);
//~^ ERROR: use of mutable static //~^ ERROR: use of mutable static
//~| ERROR: dereference of raw pointer
fn main() { fn main() {
let _ = unsafe { DEREF_BYTE_PTR }; let _ = unsafe { DEREF_BYTE_PTR };

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@ -14,6 +14,6 @@ LL | static mut DEREF_BYTE_PTR: *mut u8 = ptr::addr_of_mut!(*BYTE_PTR);
| |
= note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
error: aborting due to 2 previous errors error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0133`. For more information about this error, try `rustc --explain E0133`.

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@ -0,0 +1,14 @@
//@ check-pass
fn main() {
let ptr = std::ptr::null_mut::<i32>();
let addr = &raw const *ptr;
let local = 1;
let ptr = &local as *const i32;
let addr = &raw const *ptr;
let boxed = Box::new(1);
let ptr = &*boxed as *const i32;
let addr = &raw const *ptr;
}