generate getelementptr instead of inttoptr for ptr::invalid

rust-lang · Feb 28, 2024 · b6d7805 · b6d7805
1 parent ee933f6
commit b6d7805
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Showing 2 changed files with 32 additions and 10 deletions.
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
@@ -590,11 590,14 @@ pub const fn null_mut<T: ?Sized Thin>() -> *mut T {
 #[unstable(feature = "strict_provenance", issue = "95228")]
 pub const fn without_provenance<T>(addr: usize) -> *const T {
  // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
- // We use transmute rather than a cast so tools like Miri can tell that this
- // is *not* the same as from_exposed_addr.
- // SAFETY: every valid integer is also a valid pointer (as long as you don't dereference that
- // pointer).
- unsafe { mem::transmute(addr) }
  // FIXME(maybe): simply transmute the address once codegen lowers that correctly.
  // We offset the null pointer instead of using a cast so that this lowers to
  // getelementptr instead of inttoptr.
  // We use transmute instead of casting so that in miri the pointer truly
  // has no provenance.
  // SAFETY: on all current platforms, usize and pointers have the same layout,
  // and the validity invariant of pointers is the same as that of integers
  unsafe { mem::transmute::<_, *const T>(0usize).wrapping_byte_add(addr) }
 }
 
 /// Creates a new pointer that is dangling, but well-aligned.
@@ -632,11 635,14 @@ pub const fn dangling<T>() -> *const T {
 #[unstable(feature = "strict_provenance", issue = "95228")]
 pub const fn without_provenance_mut<T>(addr: usize) -> *mut T {
  // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
- // We use transmute rather than a cast so tools like Miri can tell that this
- // is *not* the same as from_exposed_addr.
- // SAFETY: every valid integer is also a valid pointer (as long as you don't dereference that
- // pointer).
- unsafe { mem::transmute(addr) }
  // FIXME(maybe): simply transmute the address once codegen lowers that correctly.
  // We offset the null pointer instead of using a cast so that this lowers to
  // getelementptr instead of inttoptr.
  // We use transmute instead of casting so that in miri the pointer truly
  // has no provenance.
  // SAFETY: on all current platforms, usize and pointers have the same layout,
  // and the validity invariant of pointers is the same as that of integers
  unsafe { mem::transmute::<_, *mut T>(0usize).wrapping_byte_add(addr) }
 }
 
 /// Creates a new pointer that is dangling, but well-aligned.

diff --git a/tests/codegen/strict-provenance.rs b/tests/codegen/strict-provenance.rs
@@ -0,0 1,16 @@
 //@ compile-flags: -O
 
 #![crate_type = "lib"]
 #![feature(strict_provenance)]
 
 use std::ptr;
 
 // CHECK-LABEL: ptr @without_provenance(
 // CHECK-SAME: [[USIZE:i[0-9] ]] noundef �dr)
 #[no_mangle]
 fn without_provenance(addr: usize) -> *const () {
  // CHECK: start
  // CHECK-NEXT: %0 = getelementptr i8, ptr null, [[USIZE]] �dr
  // CHECK-NEXT: ret ptr %0
  ptr::without_provenance(addr)
 }