Implement core::arch::return_address and tests

Fix typo

Apply suggestions from code review

Wording/docs changes.

Co-authored-by: Ralf Jung <post@ralfj.de>

Change signature according to Ralf's comment

Fix call to `core::intrinsics::return_address()` according to the new signature

Add cranelift implementation for intrinsic

Change wording on `return_address!()` to be clear that returning a null pointer is best-effort.

Fix formatting of doc comment

Fix mistake in cranelift codegen

Author: chorman0773

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -1529,6 +1529,12 @@ fn codegen_regular_intrinsic_call<'tcx>(
             fx.bcx.set_cold_block(fx.bcx.current_block().unwrap());
         }
 
+        sym::return_address => {
+            let val = fx.bcx.ins().get_return_address(fx.pointer_type);
+            let val = CValue::by_val(val, ret.layout());
+            ret.write_cvalue(fx, val);
+        }
+
         // Unimplemented intrinsics must have a fallback body. The fallback body is obtained
         // by converting the `InstanceKind::Intrinsic` to an `InstanceKind::Item`.
         _ => {

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -789,6 +789,12 @@ impl<'ll, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                 }
             }
 
+            sym::return_address => {
+                let ty = self.type_ix(32);
+                let val = self.const_int(ty, 0);
+                self.call_intrinsic("llvm.returnaddress", &[], &[val])
+            }
+
             _ => {
                 debug!("unknown intrinsic '{}' -- falling back to default body", name);
                 // Call the fallback body instead of generating the intrinsic code

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -120,7 +120,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 | sym::contract_checks
                 | sym::atomic_fence
                 | sym::atomic_singlethreadfence
-                | sym::caller_location => {}
+                | sym::caller_location
+                | sym::return_address => {}
                 _ => {
                     span_bug!(
                         span,

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -180,6 +180,7 @@ fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hi
         | sym::ptr_guaranteed_cmp
         | sym::ptr_mask
         | sym::ptr_metadata
+        | sym::return_address
         | sym::rotate_left
         | sym::rotate_right
         | sym::round_ties_even_f16
@@ -812,6 +813,8 @@ pub(crate) fn check_intrinsic_type(
         | sym::atomic_xor => (2, 1, vec![Ty::new_mut_ptr(tcx, param(0)), param(1)], param(0)),
         sym::atomic_fence | sym::atomic_singlethreadfence => (0, 1, Vec::new(), tcx.types.unit),
 
+        sym::return_address => (0, 0, vec![], Ty::new_imm_ptr(tcx, tcx.types.unit)),
+
         other => {
             tcx.dcx().emit_err(UnrecognizedIntrinsicFunction { span, name: other });
             return;

compiler/rustc_span/src/symbol.rs

@@ -1657,6 +1657,7 @@ symbols! {
         residual,
         result,
         result_ffi_guarantees,
+        return_address,
         return_position_impl_trait_in_trait,
         return_type_notation,
         riscv32,

library/core/src/arch.rs

@@ -76,3 +76,29 @@ pub macro global_asm("assembly template", $(operands,)* $(options($(option),*))?
 pub fn breakpoint() {
     core::intrinsics::breakpoint();
 }
+
+/// The `core::arch::return_address!()` macro returns a pointer with an address that corresponds to the caller of the function that invoked the `return_address!()` macro.
+/// The pointer has no provenance, as if created by `core::ptr::without_provenance`. It cannot be used to read memory (other than ZSTs).
+///
+/// The value returned by the macro depends highly on the architecture and compiler (including any options set).
+/// In particular, it is allowed to be wrong (particularly if inlining is involved), or even contain a nonsense value.
+/// The result of this macro must not be relied upon for soundness or correctness, only for debugging purposes.
+///
+/// As a best effort, if a useful value cannot be determined (for example, due to limitations on the current codegen),
+/// this macro tries to return a null pointer instead of nonsense (this cannot be relied upon for correctness, however).
+///
+/// Formally, this function returns a pointer with a non-deterministic address and no provenance.
+///
+/// This is equivalent to the gcc `__builtin_return_address(0)` intrinsic (other forms of the intrinsic are not supported).
+/// Because the operation can be always performed by the compiler without crashing or causing undefined behaviour, invoking the macro is a safe operation.
+///
+/// ## Example
+/// ```
+/// #![feature(return_address)]
+///
+/// let addr = core::arch::return_address!();
+/// println!("Caller is {addr:p}");
+/// ```
+#[unstable(feature = "return_address", issue = "154966")]
+#[allow_internal_unstable(core_intrinsics)]
+pub macro return_address() {{ core::intrinsics::return_address() }}

library/core/src/intrinsics/mod.rs

@@ -3589,3 +3589,16 @@ pub const fn va_copy<'f>(src: &VaList<'f>) -> VaList<'f> {
 pub const unsafe fn va_end(ap: &mut VaList<'_>) {
     /* deliberately does nothing */
 }
+
+/// Returns the return address of the caller function (after inlining) in a best-effort manner or a null pointer if it is not supported on the current backend.
+/// Returning an accurate value is a quality-of-implementation concern, but no hard guarantees are
+/// made about the return value: formally, the intrinsic non-deterministically returns
+/// an arbitrary pointer without provenance.
+///
+/// Note that unlike most intrinsics, this is safe to call. This is because it only finds the return address of the immediate caller, which is guaranteed to be possible.
+/// Other forms of the corresponding gcc or llvm intrinsic (which can have wildly unpredictable results or even crash at runtime) are not exposed.
+#[rustc_intrinsic]
+#[rustc_nounwind]
+pub fn return_address() -> *const () {
+    core::ptr::null()
+}

tests/codegen-llvm/intrinsics/return_address.rs

@@ -0,0 +1,10 @@
+#![crate_type = "lib"]
+#![feature(core_intrinsics, return_address)]
+
+// CHECK-LABEL: @call_return_address_intrinsic
+#[no_mangle]
+#[inline(never)]
+pub fn call_return_address_intrinsic() -> *const () {
+    // CHECK: call ptr @llvm.returnaddress(i32 0)
+    core::intrinsics::return_address()
+}