Rollup merge of rust-lang#139113 - folkertdev:sanitizer-unstable-book-check-block, r=GuillaumeGomez

unstable book: in a sanitizer example, check the code

Use some `#` directives to make sure the code checks on x86_64, and does not produce errors on other platforms. This example still used an older version of `#[naked]`, and because the snippet was ignored that was missed before.

I'm not sure when this gets built on CI exactly, so it might be worthwhile to try and build it for a non-x86_64 architecture to make sure that works. I'm not sure how to verify locally that e.g. on aarch64 this code works without errors/warnings.

Author: jhpratt

src/doc/unstable-book/src/compiler-flags/sanitizer.md

@@ -244,36 +244,36 @@ See the [Clang ControlFlowIntegrity documentation][clang-cfi] for more details.
 
 ## Example 1: Redirecting control flow using an indirect branch/call to an invalid destination
 
-```rust,ignore (making doc tests pass cross-platform is hard)
+```rust
 #![feature(naked_functions)]
 
-use std::arch::asm;
+use std::arch::naked_asm;
 use std::mem;
 
 fn add_one(x: i32) -> i32 {
     x + 1
 }
 
+# #[cfg(not(target_arch = "x86_64"))] pub extern "C" fn add_two(_: i32) {}
+
 #[naked]
+# #[cfg(target_arch = "x86_64")]
 pub extern "C" fn add_two(x: i32) {
     // x + 2 preceded by a landing pad/nop block
     unsafe {
-        asm!(
-            "
-             nop
-             nop
-             nop
-             nop
-             nop
-             nop
-             nop
-             nop
-             nop
-             lea eax, [rdi+2]
-             ret
-        ",
-            options(noreturn)
-        );
+        naked_asm!(
+            "nop",
+            "nop",
+            "nop",
+            "nop",
+            "nop",
+            "nop",
+            "nop",
+            "nop",
+            "nop",
+            "lea eax, [rdi+2]",
+            "ret",
+        )
     }
 }